Summary and notes re: Thyroid growth and cancer, by Dillwyn Williams

1. Williams re Thyroid Growth and Cancer
(These are notes shared with the Safecast community on the Safecast Radiation
Discussion Google group)
As many who have been following this discussion already know, Sir Dillwyn
Williams is a leading thyroid cancer specialist (an endocrine pathologist, to be
exact) based at Cambridge Univ., who along with Keith Baverstock played a
major role in recognizing that the increase in childhood thyroid cancer after
Chernobyl was in fact due to radiation exposure, and in pushing to have
protection guidelines changed to help guard against this risk. He is a leading
expert in radiation-induced thyroid cancer, with decades of hands-on
experience, and held in great esteem by his peers. Williams has not been
directly involved in investigating thyroid cancers found in Fukushima, but has
been following the developments closely. He has rarely spoken in public about
Fukushima, or written about it, but he recently published a significant paper
attempting to shed light on what the Fukushima screening results indicate
about thyroid carcinogenesis in general. It’s available here, but unfortunately
is paywalled:
Thyroid Growth and Cancer
Williams D., European Thyroid Journal, Vol. 4, No. 3, 2015
http://www.karger.com/Article/Abstract/437263
I want to stress again that Williams is an impeccable scientist and utterly
unbiased. This paper is based on an award-winning lecture he gave last
December to the European Thyroid Association. Williams has always
responded quickly to questions and inquiries we have sent him, and has
usually given permission to share his opinions here and elsewhere. I’ve
spoken with him about this paper, and will quote and summarize the most
relevant sections. I apologize in advance for the length.
Azby Brown
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From our recent correspondence:
“The two basic proposals, or if you like hypotheses based on a range of
disparate pieces of evidence, that most thyroid cancers originate in childhood
and those that have not acquired independence from the mechanisms limiting
the growth of normal follicular cells by adulthood almost all remain as very
low-grade 'cancers' throughout life have implications for the Fukushima study.”
Comment: IOW, even thyroid cancers that becomes apparent in adulthood are
probably present as small tumors during childhood. Most of these small
tumors do not “escape” and grow into large tumors, but remain small. They
are extremely common.

2. +++++
“I think that starting the [Fukushima thyroid screening] study was justifiable,
although the scope could with hindsight have been much more restricted.
Having started it, resection of the cancers was the right thing to do, the
criticism in the Lancet letter was not justified because it is not correct to
assume that the indolent behaviour of small PTCs in older adults will apply to
small PTCs in children.”
Comment: Williams has previously expressed the opinion that both the age
range and geographic range of the Fukushima thyroid screening should have
been much more limited. In the past he has suggested it would have been
better to limit it to children under the age of 14 at time of exposure, and areas
where the estimated thyroid doses were 10mGy and over. This would have
resulted in a much smaller but more informative study, and more than
adequate to identify possible radiogenic thyroid cancers. Contrast this with
increasingly strident calls from some who insist that the thyroid screening
should be extended to older age groups and also to other prefectures
(specifically, Toshihide Tsuda, of Okayama Univ).
On the other hand, while he has often expressed concern that one result of
the Fukushima screening will be overdiagnosis and overtreatment, Williams
believes that the thyroid operations done in Fukushima so far have not been
overtreatment. He considers them justified, based on the pathology of the
cancers removed.
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“The analysis leads to the very interesting proposal that the small PTCs
detected by screening in early life represent more rapidly growing tumours
which have a higher chance than those detected later of progression to
clinically significant cancers. Resecting these may reduce the incidence of
clinically significant cancers in the next decade or two.”
Comment: Williams hypothesizes that there are actually two kinds of thyroid
tumors, one type which grows quickly and another that stays small throughout
life, and that the Fukushima screening is identifying normal, non-radiogenic
thyroid cancers of the quickly growing type. Because these are being caught
early, the incidence of thyroid cancer in the screened population may be
reduced in coming decades. He goes on to say that, “This might be
detectable, possibly only if screening was stopped in the population of the less
exposed areas.”
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“It becomes ever more important to involve informed, influential and
independent members of the Fukushima public in the decisions. I hope the
paper may help a little with the information part.”
Comment: I couldn’t agree more.

3. ++++++
As a follow-up, I sent Williams the latest results (From Aug 2015), and asked
“Are you still concerned with possible over-diagnosis and over-treatment in
Fukushima, however? If so, how would you characterize that concern now?”
This is his response:
“Thanks again for the latest info, as you said there are no major surprises. The
main problems in my view lie in the future, and involve the possibility of
overtreatment, continuing exacerbation in the population of fear of future
radiation induced cancer, and lack of complete coverage, possibly missing
cancers and giving incomplete data. The Chernobyl and ABomb evidence
shows that the risk is strongly age at exposure and dose related. The older
groups from the larger part of the Prefecture will have such a low risk that the
vast majority of thyroid cancers discovered in these will represent the normal
incidence. Unfortunately the recorded incidence in this group will be affected
by the personal financial implications of agreeing to treatment, assuming this
is still the case. As the population ages, the chance that a small cancer found
on scan poses any lifetime risk to the patient diminishes, and in my opinion
there comes an age when the risks of treatment of a scan discovered small
papillary cancer outweigh the risks of doing nothing. The problem is that there
is no consensus as to what that age is. Also the numbers of cases found will
continue to increase as the population ages, and will reach a point where the
burden on the health services and the finance involved will lead to pressures
to reduce screening, and if this is not carefully managed will increase mistrust
among the population. I expect that some thought is already being given to
this by the committee overseeing the programme.”
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From the paper (emphasis mine):
“Evidence from Fukushima
The importance of imaging techniques in determining the recorded incidence
of thyroid cancer and the problems posed by the increasing frequency of
detection of small thyroid carcinomas are brought into sharp focus by the
results of screening the population exposed to fallout from the 2011
Fukushima nuclear power plant accident….
…The scale of the apparent increase has led to considerable concern in the
exposed population [15]. Nodules of less than 5 mm were not subject to
further investigation, so the true thyroid cancer prevalence can be
assumed to be much greater. However, the evidence from age at
exposure and latency suggests that the large number of thyroid cancers
so far detected is not due to radiation from the accident.
Comment: Williams has been reviewing the Fukushima thyroid screening

4. findings since 2012 very closely. The recent paper is based on findings
available as of Dec 2014, but after reviewing results released to date,
including those from August 2015, his opinion that the thyroid cancers found
so are in Fukushima are not due to radiation has not changed.
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“After Chernobyl the risk was greatest in those who were infants at the time of
the accident, falling rapidly with increasing age [8]. None of the Fukushima
cases so far were infants at the time of the accident, the youngest was aged
6, and the majority were adolescents [13] (fig. 2)“
Comment: This remains one of the strongest arguments against the
Fukushima thyroid cancers discovered so far being due to radiation exposure.
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“The first year’s screening found a similar incidence and tumour size as other
areas in subsequent years. Even with ultrasound it would seem biologically
almost impossible for cells with the initial radiation-induced mutation to acquire
the additional changes needed to give a cancer and to reach a detectable size
within 1 year after the accident.”
Comment: This is an important observation.
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“The amount of radioiodine released from Fukushima is reported to be
approximately one seventh of that released from Chernobyl [16]. That
UNSCEAR report has been criticised for using the lower of the estimates
available [17], but the higher estimate is still less than a third of that from
Chernobyl, and most of the activity released from the Fukushima accident was
blown out to sea. Few early direct thyroid measurements were made in the
immediate aftermath of the tsunami; using reconstructed doses the maximum
absorbed dose to a child’s thyroid from Fukushima fallout has been estimated
as 66 mGy compared to 5,000 mGy after Chernobyl [16]. A low level of dietary
stable iodine increases the risk of radiation-induced thyroid cancer [18];
dietary iodide was low in the areas around Chernobyl, but is high in Japan.
Each of these separate pieces of evidence suggests that the high
prevalence of thyroid carcinoma found in the first 3 years was not
related to the accident.”
Comment: Williams acknowledges the uncertainties in thyroid dose estimates,
and cites Baverstock's criticism of the UNSCEAR report (ref #17), but even
taking these into account he considers the conclusion very strong.
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“In the absence of any other known cause of a massive apparent
increase in thyroid cancer incidence, the current findings must

5. represent the normal situation, uncovered by highly sensitive
ultrasound.”
Comment: Again, this conclusion is supported by almost all reputable thyroid
cancer experts, and has been since 2012..
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“Although there is no evidence of a radiation-related increase in thyroid
cancer in the first 3 years after the accident, it is likely that one will
occur. The level of exposure combined with the high dietary stable iodine
suggests that it will be on a much smaller scale and with a longer latent period
than after Chernobyl. One forecast suggests it could be 6% of the normal
incidence [19].”
Comment: This is a very important point. It is likely that radiation exposure will
cause an increase in thyroid cancer in Fukushima, and Williams uses Jacob et
al’s 2014 estimate (the best done so far, though not without caveats) that the
increase could be of the order of 6% over the normal incidence, and will have
a longer latency period than seen after Chernobyl. Again, an increase of 6%
will be difficult to detect, unless the screening protocols are adjusted to focus
on the most at-risk cohorts, as described above.
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“The evidence from Fukushima shows that many more thyroid
carcinomas than were previously realised must originate in early life.”
Comment: This appears to be the true lesson from Fukushima so far in
relation to thyroid cancer.
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“The questionable benefits from lobectomy, thyroidectomy, or radioiodine
therapy for small papillary carcinomas in adults have to be balanced against
the known risk of complications….
…Current guidelines should reconsider their advice on the treatment of thyroid
carcinoma in view of the likely continuing increase in incidentally discovered
tumours and the findings from Chernobyl and Fukushima.”
Comment: IOW, Williams proposes that it is important from a medical and
ethical point of view to carefully balance treatment to the negative
consequences of treatment, in particular, to avoid unnecessary treatment of
slow-growing thyroid carcinomas. As stated above, he feels that the thyroid
operations carried out so far in Fukushima have been justified, but urges
caution going forward.
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“This analysis suggests that there is a biological distinction between so-called

6. micro- and macro-papillary carcinomas; a separation based purely on size is
not tenable.”
Comment: This is probably the most medically important hypothesis Williams
makes in the current paper.
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“The choice of size as a criterion reflects the divergence in later life of those
tumours with and those without escape from growth limitation. It is not
applicable to small cancers in children, and its importance in young adults is
not clear. This is relevant to the treatment of screen-detected micro-
carcinomas in young people, as after Fukushima. It has been suggested that
resection is overtreatment since these are micro-carcinomas [15], but
the evidence based largely on studies in older patients should not be
applied to adolescents and very young adults. Follow-up studies of the
cohort in Fukushima should provide very valuable evidence on the
incidence of very small lesions, and the effect of resection of early
micro-lesions on the later frequency of larger tumours.”
Comment: One of the most important lessons to be drawn from the
Fukushima thyroid survey results so far is the information it provides about the
development of normal thyroid cancer.
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