CRC Case Closed Transcript.pdf

CRC Case Closed: Guidelines for Biomarker Testing
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Case Closed: Utilizing Biomarkers in the Management of Metastatic Colorectal Cancer
Module 1: Guidelines for Biomarker Testing
Hi, my name is Dr. Benny Johnson. I'm an Assistant Professor in GI medical oncology at
the MD Anderson Cancer Center. Thank you for joining this session regarding guidelines
for biomarker testing.
The one thing we know about metastatic colorectal cancer is in 2011, really the
actionability of colorectal cancer was quite simple. The presence or absence of a KRAS
mutation really guided the use of anti-EGFR antibodies.
But in 2022, the landscape has become much more complex in a good way. You can
see there's many more mutations, and fusions that we're interested in that are actually
targetable. This is actually resulting in more precision oncology in metastatic colorectal
cancer. And we can actually think about it based on the presence or absence of
certain mutations, such as KRAS. And now, we're breaking that further into G12C versus
non-G12C.
There's possibility here for targetable therapies. Same for BRAF mutations. We're looking
at the non-V600 versus V600, and we know that the V600E now have targetable options
as well, such as encorafenib and cetuximab. In terms of mismatch repair status, we are
also aware that there is now immune checkpoint inhibitors that are available for this
population of patients, both in the frontline and refractory setting. Similarly, for HER2
amplification, we know that there is now many options considering HER2 amplification
in colorectal cancer, both dual HER2 inhibition, as well as novel targets, which we will
talk about in this talk.
More rare, but still very important to highlight, NTRK and RET fusions are now both
targetable in metastatic colorectal cancer if these can be identified. And then, we also
know about high TMB allowing for PD-1, as well as certain sub-mutations, such as POLE
and POLD that also allow for anti–PD-1 to be utilized.
Really looking at the landscape of metastatic colorectal cancer, we have many
options for patients if we find these targetable hotspots. And so what are the guidelines
for molecular profiling in colorectal cancer? Really the key is, at the very basic
minimum, we need to identify KRAS, NRAS, and BRAF mutations, as well as HER2
amplifications and MSI status, as we've seen on the previous slide.
Testing may be carried out either as individual gene testing or part of an NGS panel in
terms of the NCCN guidelines. But the key is that NGS panels actually have the ability to
pick up more rare, and as you saw on the previous slide, actionable mutations, such as
those in NTRK fusions. And so the question becomes, well, what do you do? Do you do
NGS testing panel versus single gene testing?
The guidelines really kind of give you the option for both, but I think based on the data
and as well as just real-life clinical practice, hotspot testing versus more of a panel-
based testing can result in an increased cost and probably less efficiency for you in the
clinic. Here we highlight a non-small cell lung cancer model, where the cost savings are
definitely favorable towards more of a panel-based testing.
And the second question that comes up is what about tissue versus liquid testing or
blood testing? And here we highlight a slide that shows that in many patients with
colorectal cancer, there's a good consistency or alignment between the liquid biopsy
as well as tissue biopsy results. This study that we highlight on the previous slide really

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shows that there is an option for liquid biopsy, and there's some benefits to liquid biopsy
in the upfront setting, really that there's quick turnaround time.
These are usually resulted within 7 to 14 days, and then you actually have the ability to
act on these mutations for patients, which is really, really helpful, that turnaround time.
You're not looking for tissue and trying to track that down. That's really a nice option.
The previous slide we did highlight that the frequency of genomic alterations that were
detected in cell-free DNA were comparable to those that were noted in tissue. There's
really a good consistency between the two.
That was one of the first examples of how large-scale genomic profiling and liquid
biopsies for CRC can detect genomic alterations pretty adequately as opposed to just
tissue sequencing. The other thing to think about is that liquid biopsy also, when you
think about in specific spaces of anti-EGFR rechallenge, it does give you a good
amount of insight into the tumor heterogeneity and resistance mechanisms that can
develop when patients receive certain targetable therapies. There are other additional
benefits that can be utilized for these types of assays.
I hope that we made the argument that liquid biopsy and tissue biopsy are both
effective, and that also, if you're looking to make decisions for patients, both of these
assays should be considered. The other thing is the cost savings that are there when we
do upfront panel testing, as opposed to single hotspot testing. I think that's a more
efficient approach for patients with metastatic colorectal cancer.
I think the right answer for the first question here is all-RAS testing, BRAFV600E, MMR/MSI,
HER2 amplification, and gene infusion testing. Most large scale panels, if you order
these, will provide all of these upfront. And this allows you to really kind of provide a
nice precision oncology approach for your patient with metastatic colorectal cancer.
Module 2: HER2-Positive mCRC
Next, we're going to talk about HER2-positive metastatic colorectal cancer. HER2 as a
biomarker for metastatic colorectal cancer is not necessarily prognostic. We see here
from two examples from the QUASAR and FOCUS studies that there isn't any prognostic
significance to HER2, if identified. However, there are other implications of HER2 as a
biomarker. The NCCN guidelines now include at least three different options for patients
with HER2-amplified metastatic colorectal cancer.
It is also important to keep in mind that how we find these patients actually, our yield
can increase depending on the biomarkers of the patient, so unselected population,
meaning you're not really looking at their RAF status or their BRAF status, and you're
probably not going to find them at a high yield. But if you think about KRAS wild type or
even a KRAS... or we could say all RAS wild type, BRAF wild type, our increase of yield to
find HER2 amplification is significant, especially on the left-sided colorectal cancer. This
quadruple-negative patient population is probably when you're going to find your
highest yield of HER2 amplification in a left-sided colorectal cancer that's RAS/RAF wild
type.
We also know that HER2 biomarkers can be predictive for a lack of benefit for anti-
EGFR, and so this is one of the first studies to kind of show this out of our group here at
MD Anderson, that when patients with HER2 amplification are exposed to anti-EGFR
therapy, they actually have worse progression-free survival. This was not seen with more

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with traditional chemotherapy, suggesting that there is a predictive benefit to HER2
amplification for anti-EGFR therapy. Ongoing trials are looking at what is the right
second line therapy for HER2-amplified colorectal cancer, considering this data,
comparing targeted HER2 therapy versus a more traditional cetuximab/irinotecan
approach.
This is one of the main studies that show response with dual HER2 inhibition, trastuzumab
and pertuzumab. The MyPathway study with 57 patients really showed an impressive
overall response rate of 32%. This is really exciting for these patients that you can see
that dual HER2 inhibition with IV antibodies that target HER2 are quite effective. We see
that these responses are durable, and we had a CR with many PRs for these patients.
The first study, actually, however, was the HERACLES-A study, which showed that
targeting trastuzumab with a novel tyrosine kinase inhibitor showed really nice
responses, 27 patients overall response rate of about 30%. And again, durable
responses for patients.
More recently, the DESTINY-CRC01 study was presented that showed that trastuzumab
deruxtecan also has efficacy for patients with HER2-amplified colorectal cancer. This is
a study that showed the response rates here, a 24% overall response rate in patients
that had PRs as well. The interesting thing about this study is that it did allow prior HER2
therapy, dual HER2 therapy, as we saw in the previous slides, and patients still were able
to glean a response. It is important to highlight this is mainly for the IHC3+ cohort or a
IHC2+ with an ISH+ cohort that got the most benefit from this therapy. Really a nice
selective biomarker for these patients.
The one thing to keep in mind, though, about this approach is that there is a higher risk
of interstitial lung disease that are noted, and in the protocol, there were three patients
that developed grade 5 ILD. This is important to keep in mind for us as we're treating our
patients. If we start to notice dyspnea, hypoxia, and to have a short threshold for
initiating corticosteroids, to keep a close eye on those patients, considering the data
here. So it definitely kind of, I would say, decreases the enthusiasm for this regimen, why
it's not common. Just having grade 5 toxicities, we really need to keep that in mind,
considering here, as well as the median time being about 22 days for the onset, and
within six days, these patients that were exposed to this grade 5 toxicity had passed
from this. So that's a huge thing to keep in mind.
Really exciting data was presented from the MOUNTAINEER study at ESMO that showed
that this novel tucatinib in combination with trastuzumab, a novel tyrosine kinase
inhibitor, did show really exciting data that overall response were at about 38%. It was
durable and patients had a median progression-free survival of 8.2 months with about
24.1 months of overall survival. This seems to be a very well-tolerated regimen, and for
the most part diarrhea was common for a grade 1 and grade 2 toxicities, and some
patients did experience hypertension, but other than that, there were no grade 5
toxicities as we highlighted with the T-DXd, and so this is important to keep this in mind. I
think the FDA will be reviewing this, and this may be another arsenal that we can use for
HER2-amplified colorectal cancer.
This shows the landscape currently in metastatic colorectal cancer for HER2
amplification, which is really many options. We didn't talk about TDM1 because it was
not really a study that met its primary endpoints. However, you can see the DESTINY
data and you can see the MyPathway and HERACLES data that shows the really nice
response rates, and, impressively, the MOUNTAINEER data of tucatinib and trastuzumab

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that really showed overall response rates reaching in the upper fifties with really durable
responses. This is going to be a new regimen that we're going to also have at our
fingertips. Not currently, but probably very soon.
If we look at the case, I think the best treatment for this patient as of right now is going
to be answer C, just considering that there is no direct head-to-head comparison
between any of these various regimens, so I think either dual HER2 inhibition or T-DXd
are options here—trastuzumab deruxtecan—are all options for patients.
Module 3: NTRK Fusion-Positive mCRC
Next, we're going to talk about NTRK fusion-positive metastatic colorectal cancer. So,
NTRK fusions and colorectal cancer, so these are genes that encode the tropomyosin
receptor kinase family comprised of three transmembrane proteins, TrkA, TrkB, and TrkC
receptors, which are encoded by the NTRK1, NTRK2, and NTRK3 genes, respectively.
Typically, NTRK expression is primarily in the nervous system, and these are kinases that
help regulate survival, proliferation, as well as position in terms of movement and things
in that space in the nervous system normally. When you actually have issues with NTRK
fusions, the signal transduction pathways activated by these receptors seem to be
constituently activated. Then you have an out-of-control proliferation and invasion and
angiogenesis. We have patients that really develop malignancy in this setting, so, this
constituently active pathway is then a huge issue for patients.
The incidence of fusions increases in MSI-H in CRC. We know that fusions, they're not
very common. They're only about 0.6% if you look at all comers through large NGS
panels. However, if you look at MSI-H patients specifically, you do see that these
patients that have MSI high have a higher incidence of fusions. That actually goes from
0.6% general all comers to as high as almost 42% in MSI-H in this one study here. Really
kind of allowing us to think about, well, what is our highest yield for NTRK fusions and
identifying NTRK fusions in patients with colorectal cancer? This is another study that
showed about 20,000 solid tumor specimens about nearly 5,000 of those were
colorectal cancer specimens. And again, a very similar finding that in MSS patients, the
fusion rate was very, very low at 0.2%. But if you looked at MSI-H fusion, it was about
7.85%. This is another thing to keep in mind as you're looking for these “needle in the
haystack” mutations and fusions for patients to think about, well, what's going to be my
highest yield? Where do I expect to see this?
Another study has actually shown how can we further refine this: 2000 colorectal
cancer patients, about 21 fusions, really at a low incidence in proficient mismatch
repair/MSS, and again, at a higher incidence in deficient mismatch repair/MSI-H, 5%.
But then if you look at what about adding on RAS/RAF wild type status, you actually
increase that percentage, and kind of back to that number that we talked about on
the previous slide. I think the highest incidence to find NTRK fusions are actually for
patients that are MSI-H, RAS/RAF wild type, and this particular dataset shows that MLH1
hypermethylation. This is kind of the three key aspects to really increase your yield to
finding an NTRK fusion. I think when you're looking at patients in the clinic and you start
having MSI-H patients that have some refractory disease, you want to also make sure
that you've already ruled out NTRK fusions, if you have not yet done gene fusion testing.

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This kind of goes back to precision algorithms for genomic testing. Now, the very first
question of this program we talked about, well, do you include gene fusion testing out
of the gate? And I think most large panels, commercial panels will provide gene fusion
testing. You'll have that data, but what if you were more of the believer of hotspot
testing, how would you be more refined in your decision making for when to send off
gene fusion testing if you had limited tissue? This kind of shows us that if you look at the
MSI status and you have an MSI-H or mismatch repair deficient patient that has MLH1
hypermethylation, you're thinking two things: you're thinking they either have a sporadic
MSI-H from a BRAF mutation, V600 specifically. But if they're wild type, that would be a
reason to do fusion testing. You can kind of follow the algorithm that way to increase
your yield.
The other more basic approach would be if the patient does not have sporadic MSI-H
colorectal cancer and is BRAF wild type, just to go ahead and screen. And so really this
shows us that the best way may be to identify NTRK fusions in colorectal cancer are for
patients that are wild type KRAS, NRAS, and BRAF and with a sporadic MSI-H. This is
important to keep that in mind.
There are actually two FDA approved targeted agents for NTRK fusions and metastatic
colorectal cancer. These are TRK inhibitors. The first is larotrectinib. There were eight CRC
patients in this basket study, and there were really impressive response rates for this wide
array of malignancies in the refractory setting. You see really impressive response rates
were published at 79%. There's also a pan-TRK inhibitor, entrectinib, that's also available
for patients. There were three CRC patients in the study, but again, impressive response
rates of about 57% for all comers here.
These are, again, really important not to miss. In the previous slides, we highlighted how
to increase our yield, when to start thinking about it, MSI-H, RAS/RAF wild type patients,
MLH1 hypermethylation that are not related to a BRAF mutation. This is really the time to
consider NTRK fusions if you did not have the upfront panel testing. And then you have
two targetable agents here that are very effective for patients.
Going back to this case, which is actually a case from my very own clinic, this is a
patient that had a sporadic MSI-H colorectal cancer and had poor response to anti–
PD-1. When you find NTRK fusions for these patients, the next step, without a doubt, is I
would even say even beyond re-challenging immunotherapy, would maybe double it. I
would actually think that the right next step should be to utilize one of the TRK inhibitors
as an option. So that would be my recommendation for this particular case.
Module 4: BRAFV600E Mutant mCRC
Next, we're going to talk about BRAFV600E colorectal cancer. So BRAF mutations,
especially V600E, is associated with poor survival, and they have a unique clinical
presentation. They're only about 7% to 10% of colorectal cancer, and I think it's
important to know that they are distinctly different in terms of their outcomes and their
survival.
And so here, we have some data that shows how they compare to KRAS and NRAS
mutations. Clearly, you can see that BRAFV600E has a much poorer prognosis in terms
of overall survival, and they have a distinct clinical phenotype in terms of how they

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present and what their distant metastatic sites tend to be. Here are some data that
shows and highlights that. These are unique patients.
As a therapeutic target in cancer, activated BRAF perpetuates the MAP kinase activity,
and this leads to cell cycle progression and tumor cell proliferation. We know that BRAF
inhibitors had tremendous activity in metastatic melanoma, just single-agent BRAF
inhibitors. And similarly, for lung cancer and papillary thyroid cancer, as well as hairy cell
leukemia, it was quite effective. So BRAF- and MEK-targeted therapies are actually
approved in metastatic melanoma, as well as metastatic non-small cell lung cancer.
So, this type of data had us thinking, "Well, can we use a similar approach for
BRAFV600E colorectal cancer?"
However, the monotherapy studies in metastatic colorectal cancer really proved to be
not anything like our melanoma cohort. This is one of the first studies that was performed
utilizing vemurafenib or first-generation BRAF inhibitor in metastatic colorectal cancer.
Twenty-one patients and only one patient had a confirmed partial response consistent
with a response rate of about 5%, but you could see really poor progression-free survival
and overall survival, highlighting monotherapy is not an option for metastatic colorectal
cancer with BRAF mutation and that's just distinctly different from what we saw with
malignant melanoma.
So now we start thinking, "Well, what are the resistance mechanisms that are at play
here?" And I think we all know at this point that BRAF inhibition results in feedback
reactivation of EGFR, and so you have MAP kinase still being activated. What about
dual-targeted approaches? And these really propel the next wave of studies for
BRAFV600E in colorectal cancer. Understanding that this still results in KRAS and EGFR
amplifications, MEK and RAS mutations. Additional thoughts were, "Well, maybe we can
add triple therapy with a MEK inhibitor to deal with some of these resistance
mechanisms." But clearly, it wasn't going to be a single agent approach that would be
effective in colorectal cancer, really kicking off many clinical trials to identify what is the
best combination approach?
SWOG 1406 is one of the first targeted approaches for BRAFV600E combination. At the
time, cetuximab/irinotecan was an available second line option. It was actually the
comparator arm here. And you could see vemurafenib, when added irinotecan and
cetuximab, did show improvement for patients. It was the first to show improvement for
patients with BRAFV600E, the first clinical trial to actually meet its primary objective and
had improved response rates and also progression-free survival. This was exciting for us
as an initial option for patients with BRAFV600E. So, this was our very first clinical
response.
Well, what about adding MEK inhibition with BRAF and anti-EGFR? Would that result in
further survival? The BEACON, the large phase three study, that randomized patients
with refractory BRAFV600E colorectal cancer, about 665 patients that were randomized
encorafenib, cetuximab, and binimetinib; encorafenib, cetuximab; or irinotecan and
cetuximab really showed that the experimental arms had significantly improved overall
response rates of 26% and 20%. The primary endpoint really here was overall survival of
the triplet arm versus control. Clearly, this approach is better than the standard of care
at the time.
The BEACON phase 3 survival outcomes, you could see that the triplet and the doublet
arms both result in improved median overall survival of 9.3. The primary endpoints of
overall response rate and overall survival were met. However, it was important, and I

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think surprising for us, when this data was read out that there was no overall survival
difference between encorafenib and cetuximab versus encorafenib, cetuximab, and
binimetinib. When this was reviewed by the FDA and from the treating investigators, it
really was encorafenib and cetuximab that became the FDA-approved option for
patients with colorectal cancer, not exposing patients to needless toxicity with the
triplet. There are ongoing translational studies to see if there are certain patients that
may benefit from a triplet approach, but as of April of 2020, the FDA approved
encorafenib and cetuximab as a viable option for patients in the refractory setting.
This really highlights the pathway to precision therapy for BRAF mutations. We
highlighted the vemurafenib monotherapy clinical trial that showed a very poor overall
response rate of 5%. You can see how far we've come with many studies looking at
doublet approaches, such as vemurafenib, cetuximab, and irinotecan, but you can
see there were other doublet and triplet approaches that were utilized. With each
combination, we see incremental benefit until we reached 2020 with the successful
encorafenib and cetuximab, allowing for FDA approval and the current standard of
care in the second line setting for patients with BRAFV600E.
I think the one thing that this slide highlights is just the amount of time it takes to really
identify successful precision therapy in colorectal cancer due to the multiple resistance
mechanisms that we know occur in MAP kinase pathway. It also highlights what good
translational science can do for patients and shows the building blocks that were
necessary to reach the approval for encorafenib and cetuximab, led by Dr. Kopetz and
colleagues.
It is also important to highlight the BREAKWATER study, which is actually moving BRAF
and EGFR to the frontline. This is going to result in improved response rates for patients,
especially in combination with chemotherapy. The safety lead-in has been presented,
and there have been some signals there. I think that's really important to keep in mind
that this targeted combination, may work synergistically with standard-of-care
chemotherapy.
This large phase 3 study that has three arms, looking at encorafenib and cetuximab
versus standard-of-care chemotherapy versus the control arm of physician's choice
available standard-of-care chemo, these are going to have key primary endpoints. The
key secondary endpoints that really is going to speak to whether or not moving
targeted therapy to the frontline is going to result in increased survival outcomes for
patients. I think the answer here is going to be, yes. I think the data will be very
interesting to see how arm A compares to arm B, and how much additional benefit
patients glean from the synergistic effects of chemotherapy. It'll be an important
readout for us and really improve the landscape for patients with BRAFV600E colorectal
cancer.
Looking at our case here, after initial triplet chemotherapy, which is supported by a lot
of the initial data for patients with BRAFV600E, considering how aggressive their disease
is and until we have readout from the BREAKWATER study, I think for this particular
patient, it's pretty straightforward that after they have progression on standard-of-care
chemotherapy, the next best therapy option for them, if in fact they're microsatellite
stable, is going to be encorafenib and cetuximab. That would be our recommendation
for this patient.

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Module 5: MSI-H/dMMR mCRC
Our next focus is going to be mismatch repair-deficient colorectal cancer, or MSI-high.
MSI-high or deficient mismatch repair colorectal cancer is about 4 to 5% of metastatic
colorectal cancer. Some important clinical features are these patients are right-sided,
in terms of their primary tumor side. They have lymphocytic infiltrates, the histology is
usually poorly differentiated, and they do have good prognosis in early stages.
Molecularly you're talking about loss of the MMR protein, and this results in variation in
microsatellite lengths and tremendous increased tumor mutational burden due to the
generation of thousands of mutations. The etiology could be germline with the most
common being Lynch syndrome, versus sporadic MSI-high via MLH1 hypermethylation,
which can be associated with BRAF V600E, or bialleic alterations.
Currently MSI-high as a biomarker for metastatic colorectal cancer really has resulted in
options for patients in both the frontline and in the refractory settings. If we're looking at
the timeline, back in May of 2017, pembrolizumab was approved for patients and
nivolumab was subsequently approved. And even the doublet is now an option for
patients in the second-line or refractory setting. More recently we have frontline data to
support checkpoint inhibition pembrolizumab for treatment-naive MSI-high colorectal
cancer, and so we'll review some of that data now.
These are some of the landmark data for microsatellite instability-high colorectal
cancer. We have the New England Journal of Medicine paper that really put this on the
map in terms of using checkpoint inhibition for patients with the dMMR CRC: 28
patients, a very impressive response rate of 57% and disease control rate at 89%. But I
think what is key is that the proficient patients really had zero response. I think that's
really important to keep that in mind, that this is distinctly for MMR deficient patients.
Since that time, we have other data sets with pembrolizumab that show impressive
overall response rates from both the Keynote studies, as well as nivolumab and
nivolumab/ipilimumab, all with impressive response rates for patients. More recently, the
Keynote 177 was a frontline MSI-high colorectal study randomizing patients to standard-
of-care chemotherapy versus pembrolizumab. And the study did meet its primary
endpoint of progression free survival, as you can see here. All patients benefited in
terms of response, most notably the BRAF patients. It was important to keep that in
mind.
Interestingly, some of the RAS patients did not- gleaned more benefit from
chemotherapy. You can look at the curves here and you can see that there are a
percentage of patients that not all patients will respond to this. I think we know that
data now, and it's important to keep that in mind. But nonetheless, for the majority of
patients with deficient mismatch repair colorectal cancer, immunotherapy upfront is
the standard of care, considering the median progression-free survival was nearly
doubled with pembrolizumab.
Here we highlight that there was PD in about 30% of patients. It's kind of what we see
clinically that some of these patients just don't respond to immunotherapy. That is
important to keep that in mind, and we highlighted in the previous sections that some
of these patients could be in NTRK fusion patients and may have an option there, versus
some that are just intrinsically resistant to immunotherapy. Additional studies are
needed for patients like this, novel approaches either that could be exposing them to
subsequent doublet immunotherapy, nivolumab/ipilimumab, or even novel clinical trials
that look at altering the tumor microbiome, things like fecal transplants in combination

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with checkpoint inhibition. All of these kind of novel approaches are necessary for these
patients, these 30% or so that seem to be resistant to immunotherapy up front.
Here's another frontline data set from nivolumab/ipilimumab, the Checkmate-142. And
again, this shows really effective and durable responses recently updated. You can
really see that with a follow up of greater than two years: there's about 45 patients, they
had an overall response rate of about 69%, a CR of about 13% and disease control rate
of 84%. These responses are really durable. They're not limited by the patient's mutation
status, specifically KRAS or BRAF. The median progression-free survival and overall
survival have not yet been reached. While keeping in mind that this is not a randomized
data set, it still is important that this data has allowed us to utilize this approach as well
in the frontline setting, in the NCCN guidelines.
One thing we do want to keep in mind, and I'd been alluding to it earlier in the talk, is
that immunotherapy for BRAF V600E is an option for patients that are MSI-high, and so
we do know that sporadic MSI-high can be associated with BRAF V600E mutations or
MLH1 hypermethylation. These patients, considering the historical data that we know
about BRAF V600E, the question arises, are they going to respond to immunotherapy, or
do they need targeted therapy that is focused on BRAF mutation itself? This data is
really for the BRAF subgroup that are MSI-high actually just confirms that these patients
should be exposed to immunotherapy up front. They had nice response rates to both
nivolumab and nivolumab/ipilimumab, with excellent disease control rate. Patients with
BRAF V600E MSI-high should in fact be exposed to immunotherapy in the frontline
setting. I think that's really important to highlight that and keep that in mind for all of
your BRAF V600E patients, that we should be screening them for MSS status, considering
this data. Just highlighting immune checkpoint blockade is safe and effective option for
MSI-high BRAF V600E, and especially in the front, so this is not an issue for these patients.
Looking at our case, what should be the frontline option for these patients? The answer's
going to be pembrolizumab or nivolumab alone, or in combination ipilimumab, as we
look at the Checkmate data, and also highlighting that referral for genetic testing.
Obviously, these patients could have familial syndromes, most commonly being Lynch
syndrome, and so we want to make sure that we're doing genetic testing as well, too.
Module 6: Emerging Targetable Subsets in CRC
Finally, we're going to talk about a few emerging targetable subsets in colorectal
cancer. KRAS G12C is a very unique subtype of metastatic colorectal cancer. Here's
some data from our institution that really shows that these patients have distinct
response to standard-of-care chemotherapy. and actually have, I would say, pretty
poor progression free survival in the second- and third-line settings. When you compare
G12C KRAS mutations to non-G12C, they have worse overall survival. And so again, this
is only 3% of metastatic colorectal cancer, but they do have distinct clinical outcomes
and only have modest benefit to standard-of-care chemotherapy. We do know that
there is increased activation of EGFR in these patients, and there are very exciting anti-
EGFR and G12C inhibitor combinations that are currently underway, and we have
some readouts for that we can discuss in a few slides.

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One of the first data sets to look at targeting G12C come from sotorasib therapy in
G12C colorectal cancer. And this is a New England Medicine paper that really shows
again, a very similar story to what we unfortunately saw with our BRAF B600E colorectal
cancer experience that monotherapy in colorectal cancer seems to not be effective
unlike other histologies such as lung, as in this example. The partial response rate for
colorectal cancer was only about 3%. And so again, the duration of SD was about 5.4
months, and medium progression-free survival is only about four months. Monotherapy
seems to not be enough for G12C colorectal cancer.
This is mainly because there are many adaptive mechanisms of resistance to G12C
inhibition. We highlight some of those here, both innate and adaptive resistance. If you
use single-agent monotherapy to target KRAS G12C, you're going to have, again,
EGFR, increased RTK signaling that induces kind of other new KRAS-GTP, and NRAS
HRAS, so you're going to have resistance mechanisms that clearly are going to be an
issue, supporting dual targeted approaches for these molecular alterations in colorectal
cancer.
We highlight some of those resistance mechanisms here. There are multiple G12C
inhibitors. I highlight sotorasib and adagrasib, and these are, again, only about 3% of
colorectal cancer patients have G12C, but there are preclinical data to suggest that
when you combine the G12C inhibitor with EGFR inhibition, as we saw on the previous
side in terms of the reactivation pathways, you do get some nice responses. You can
highlight, and you can see here some of the preclinical data that shows the
combination of sotorasib with anti-EGFR cetuximab and this particular model resulted in
some nice tumor growth inhibition. These acquired resistance to single agent G12C
inhibition can be overcome. I think that's the path forward for G12C inhibition and
colorectal cancer.
Just very recently at ESMO, this data has been presented where we have both subsets
here looking at G12C inhibitors in combination with anti-EGFR, that these are very
active combinations for patients that have been previously treated with standard-of-
care chemotherapy. You can see both combinations of adagrasib and cetuximab,
and sotorasib and panitumumab, both have excellent overall response rates, disease
control rates, and impressive survival outcomes. This really is what I think is going to be
the next approval for a new subset incolorectal cancer, G12C. It's going to be very
exciting for our patients to find these mutations and then really use them in the
refractory space. Then there are ongoing studies to look at whether moving these
targeted approaches alone and in combination with chemotherapy in earlier line
settings will be beneficial for patients, and those studies are underway. Nonetheless,
really exciting options for patients and really supporting our decision for precision
oncology and identifying these patients early.
The next subgroup to think about are RET fusions in metastatic colorectal cancer. These
are rare alterations, probably along the order of about 1% in metastatic colorectal
cancer, but again, fitting the theme of a needle in a haystack. If you were to find a
colorectal cancer patient with one of these fusions that we can pick up on our large
panel NGS testing assays, they have quite effective responses.
We had nine CRC patients for these RET inhibitor studies with selpercatinib, the response
rate of 44% as well as pralsetinib, there was two colorectal cancer patients that
developed at least SD, but impressive response rates for all comers. Really important to

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highlight that these are options that we can offer our patients if we look for them, and if
we find them.
Another area to keep in mind that has been gaining increasing interest are POLE and
POLD1 mutations in colorectal cancer. You can see here that one of the MD Anderson
experiences that we've had here is that about 15.9% of the POLE mutations that we
picked up were deemed to be pathogenic. You can see the difference here on a
sample mutational assay that you can see the difference between a driver POLE
mutation resulting in numerous mistakes because of the proofreading defect versus a
passenger POLE mutation.
The vast majority of CRC hyper-mutators that are MSS are driven by these POLE
mutations. I think it's, again, important to look for them and to act on them if they're one
of the key mutations. This is something that we also are keeping in mind in our large
panels when we get these results back to make sure that we're taking a look at POLE
mutations. You can kind of see here that the data set here, the 141 patients, that you
could see the POLE mutations are really in patients with MSS and they have really high
tumor mutation rate, and so I think that's really important. But then the question
becomes, well, do all patients with POLE mutations respond? That's why I wanted to
show you the difference between a driver POLE mutation and a passenger POLE
mutation. This is really a nice study out of the Sloan group that shows that it's really the
proofreading deficient POLE mutations that respond to anti–PD-1.
This is a clinical trial that looked at 61 patients that had POLE mutation and they expose
them to PD-1. You could see all of the POLE mutations that actually had proofreading
deficiencies kind of clustered in this region here are the ones that really respond to anti–
PD-1. These POLE mutations with proofreading deficiencies are actually the ones that
have high TMB and therefore respond to anti–PD-1. Drastically different than these
passenger POLE mutations, so you have differences in terms of the response rate, 50%
versus 0%, and disease control rates of nearly 80%. Again, needle in the haystack, but
very important to look for these mutations. The additional data that we have here from
this slide is, those that are actually in the right domain or in the proofreading—those that
actually develop proofreading deficiencies—those are the POLE mutations that are
going to result in high tumor mutational burden and therefore response to checkpoint
inhibition, so important to keep that in mind.
Finally, we have the BRAF mutations, the atypical non-V600E mutations are also a
distinct subtype. This is only about 4% of metastatic colorectal cancer, but we do know
that these patients have distinct survival. This is one of our data sets through our MD
Anderson experience and we could see that patients do have improved survival when
compared to BRAF V600E, but still some decreased survival compared to typical wild
type. I think it's important that we highlight this set of mutations as well. It's also important
to keep in mind that the atypical BRAFs tend to be a little bit younger. They tend to
have more left-sided disease as opposed to right-sided disease in BRAF V600E. They
tend to have co-mutation with RAS, which is also distinct from BRAF V600E, which is
typically mutually exclusive from RAS mutations. They are mostly MSS; very rare to find
MSI-high for atypical BRAF.
Further complicating the issue with the atypical non-V600E is they're broken down into
functional classes based on how they signal through the MAP kinase pathway. This is
resulting in kind of a difficulty in finding the best path forwarded for targeted
approaches for these patients.

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I think it's important to identify here that there's three classes of BRAF mutations and
Class I is the traditional BRAF V600E. Class II and Class III, again, highlighting they signal
very distinctly through the MAP kinase pathway. Class II are actually RAS independent,
and they signal through BRAF dimerization, and then Class III are actually RAS
dependent and have more of a hetero-dimerization and are kinase impaired. Key
differences between the two classes as well as compared to Class I. You can see here
that the list of non-V600E mutations, both Class II and Class III, are quite long, and there
are many unclassified non-V600Es that are also picked up on large NGS panels that
we're not yet sure what to do with.
We're still learning about this unique subset in colorectal cancer, but it's important to
highlight in this talk that these are different than V600E. Early on, patients were being
treated as though they were one and the same, and we know that's not the case. Data
sets have now come out where applying the BEACON regimen of encorafenib and
cetuximab for atypical BRAF is not necessarily effective. There needs to be novel
approaches that really think about the biology of signaling through MAP kinase for
Class II and Class III. There seems to be distinct responses to chemotherapy and
targeted therapy for these unique BRAF mutations.
Here's some of the data highlighting that. This is a large cooperative group, a
cooperative effort between our colleagues in Canada and the United States. This really
shows this is kind of all histologies, but specifically for the BRAF Class II and Class III in
colorectal cancer. We can see, we definitely did in Class II, see more responses with
MEK inhibition or ERK inhibition. Then for the Class III, EGFR inhibition seems to be
effective. In our previous experience, we still do offer patients with atypical BRAF
mutations, anti-EGFR therapy in combination with chemotherapy for class III. However,
some of our data has suggested that anti-EGFR therapy may not be effective for class
two, and actually may even be a predictor of lack of benefit if you have a Class II
mutation to EGFR inhibition. A lot of work still remains to be done for this subset.
This is just a kind of summarizing a lot of this distinct signaling between these unique
classes and BRAF Class I versus Class II and Class III, and maybe some potential
strategies or paths forward, many of which are actually undergoing clinical trials in the
early phase setting now, to think about what are some rational combination strategies
for these patients. Again, representing only about 2% to 3% of metastatic colorectal
cancer, but still a reasonable subset that we have to identify and also think creatively
about in the refractory setting, and so just highlighting some of our thoughts about
these unique subsets.
To get back to our question, which one of these are actionable today? Really, it's all.
We talked about KRAS G12C with the exciting data with targeted therapies, with G12C
inhibitors in combination with EGFR. We talked about RET fusions now having two drugs
that could potentially be options for patients with colorectal cancer, with RET kinase
inhibitors. The findings of POLE and POLD1 mutations, probably not all POLE and POLD1
mutations, we showed you the data that is really the mutations that are in the
proofreading domain that result in high TMB and most likely response to anti–PD-1. Then
we just wanted to highlight the importance of BRAF non-V600E as a distinct subset from
BRAF V600E, and that those patients should have unique approaches as well, too. These
are all emerging subsets that I think are highlighting precision oncology in 2022 for
metastatic colorectal cancer and really something that we can keep in mind.

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To summarize some of the conclusions and key takeaways, given the established and
emerging molecular targets in metastatic colorectal cancer, tissue- or liquid-based
approaches for panel testing is recommended. We showed you the data to support
either are very reasonable. There have been many more data sets that have come out
since then that show that there's a high concordance between tissue and liquid
biopsies. I think upfront panel testing allows for the most precision for our patients out of
the gate, and that's something to keep in mind.
HER2 over-expressed metastatic colorectal cancer has now multiple active targeted
treatment approaches. We showed you MyPathway and HERACLES data for dual HER2
inhibition, as well as some of the exciting ADC data with trastuzumab deruxtecan and
more recently novel tucatinib in combination with trastuzumab being one of the highest
response rates that we've seen, and maybe with a much more favorable side effect
profile, so really multiple options for patients with HER2 overexpressed colorectal
cancer. And I think the same theme of whether or not moving these lines of therapy
earlier... moving these targeted approaches to the earlier line settings in combination
chemotherapy is going to be where the next steps are. But as of 2022, we have really
great options for HER2 overexpressed colorectal cancer.
We also wanted to highlight that fusions in metastatic colorectal cancer is a very
important subset to identify, but probably our yield is going to be increased best for
patients that are RAS/RAF wild-type MSI-high. I think that's our best patient to really be
thinking about fusion identification. As you saw from the data, really active drugs. Really
critical to remember that, keep that in mind to test that for our patients.
Targeted therapy for BRAF V600E colorectal cancer in the second line setting is now
standard of care, and we highlighted some of the ongoing trials to establish its role in
the frontline. We're going to have to stay tuned for the BREAKWATER data, but as of
2022, we have a really nice, targeted approach that we can offer our patients in the
second-line setting.
PD-1–based immunotherapy is now frontline therapy instead of chemotherapy for
patients with MSI-high MCRC. We looked at the Keynote-177 to support, so we should
keep that in mind for patients.
Finally, KRAS G12C, RET fusions, and POLE all represent exciting “needle in haystack”
emerging, actionable targets today in colorectal cancer, and so I think this is really
exciting for our patients and exciting for the field that we are becoming much more
precise in our approaches for tackling metastatic colorectal cancer.
We're excited to see the impact of this educational activity on patient care and
colorectal cancer. In four weeks, you'll receive a short survey to see if you've been able
to implement any of your intended changes as a result of what you learned today.
Thanks so much for joining us.

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