molecular biology and the targets for therapy

1. Molecular biology of breast
cancer

2. Is This Enough ????

3. Genetic Factors
 Oncogenes
 Tumor suppressor genes
 DNA repair genes
 Carcinogen
activating/deactivating
genes
 Cell cycle genes
 Cell cycle checkpoint
genes
 Cell death genes
 Cell signaling genes
 Cellular senescence
genes
 Cellular differentiation
genes
 Metastasis/invasion
genes

4.  Hormones
 Growth factors
 Small interfering RNAs
 Post-translational modifications
 methylation
 protein ubiquination
 phosphorylation
Epigenetic Factors

5. • Breast Cancer is caused by
heterogenous group of tumor cells
whose behaviour and response to
therapy depends on biological
features.
• Therefore biologic properties of the
tumor play an important role in its
management
Eliyatkin N et al, Journal of Breast Health 2015; 11: 59-66
Perou, C., Sørlie, T., Eisen, M. et al. Molecular portraits of
human breast tumours. Nature 406, 747–752 (2000)

6. Molecular Subtyping- Gene Expression Profiling
Measurement of activity (the expression) of thousands of genes
at the level of transcription, at once, to create a global picture
of cellular function.

7. Why do we need to do Molecular Subtyping?
Molecular testing in breast cancer is used to
– Classify tumor types,
–recognize hereditary implications (eg, BRCA1
mutations) – identify appropriate therapeutic agents (eg,
HER2+ disease or ER/PR + disease),
– Determine the prognosis of the disease by giving the
risk score,
– Identify biomarkers that can predict or monitor the
response to treatment
– To avoid unnecessary treatment to all cancer patients.
Sorlie et al;Proc Natl Acad Sci U S A. 2001 Sep 11;98(19):10869-74

8. Molecular Subgrouping Valid in Clinical Use
A panel including ER, PR, HER2, Ki67, epidermal growth factor receptor
(EGFR) and basal cytokeratins(CK14 and CK5 / 6 etc) can be used to
distinguish between “luminal”,HER2 and triple negative tumors.
There is no consensus on the determinants defining “basal” tumors,
nevertheless it is considered that the use of EGFR and CK5 / 6 can aid in
identification of this subgroup and predict prognosis
Eliyatkin N et al, Journal of Breast Health 2015; 11: 59-66

9. Intrinsic Breast Cancer Subtypes
• Luminal-like Breast Cancer Types
-Luminal A
-Luminal B
• HER2 enriched breast cancer subtype
• Basal-like breast cancer subtype
• Normal breast like subtype.
Perou, C., Sørlie, T., Eisen, M. et al. Molecular portraits of human breast tumours. Nature 406, 747–752
(2000)
Annals of Oncology 23: 2997–3006, 2012 doi:10.1093/annonc/mds586

10. Luminal A
• Derives its name from its similarity to the expression profile of normal luminal breast
epithelium.
• Overexpression of ER-regulated genes
• Underexpression of an HER2 gene cluster
• Underexpression of proliferation-related genes.
• Sensitive to endocrine manipulation( hormonal therapy).
• Less sensitive to cytotoxic agents in both the neoadjuvant and metastatic settings.
• Approximately 40% of all breast cancers are classified as luminal A.
• They have favorable prognosis

11. Luminal B
• Have lower expression of ER-related genes
• Variable expression of an HER2 cluster of genes,
• Relatively higher expression of proliferation related genes Ki67,FGF1,P13K.
• They represent about 20% of breast cancers.
• They also been shown to have genomic instability, and to harbor mutations in
TP53.
• less sensitive to cytotoxic chemotherapy, sensitive to hormonal therapy
• Associated with a relatively higher risk of relapse.

12. Mediators of Oestrogen Oncogenic effect

13. Activation of ER by phosphorylation induced by growth factor
and cytokine signaling pathways.
Rasmus Siersbæk et al. Genes Dev. 2018;32:1141-1154
© 2018 Siersbæk et al.; Published by Cold Spring Harbor Laboratory Press

14. HER2 enriched breast cancer subtype
• It is characterized by high expression of
– HER2
– Proliferation genes
• low expression of luminal clusters.
• Constitute 20% to 30% of all breast
tumors.
• Clinically, they are associated with a
poorer prognosis

15. HER2 enriched breast cancer subtype contd..
HER2 overexpression results in increased
HER2 containing dimers of all kinds.
 Increased HER2-EGFR dimers drive
proliferative and invasive functions.
 Increased HER2 homodimers disrupt
cell polarity.
 Increased HER2-HER3 dimers drive
proliferative, survival, invasive, and
metabolic functions.
 Increased HER2 expression results in an
increase in the rare ΔHER2 isoform with
more potent signaling characteristics.
 Several transcription factors are induced
in HER2 overexpressingcells resulting
in a plethora of gene expression
changes.
Oncogene. 2007 Oct 4; 26(45): 6469–6487.

16. Basal Like
• Constitute about 15% of invasive ductal breast cancers.
• Its name is derived from shared gene expression patterns with normal basal
epithelial cells.
• They are considered ER/PR and HER2 negative (“triple negative”)
• This subtype is also characterized by relatively high frequency of BRCA1
mutations, increased genomic instability,
• High expression of the proliferation cluster of genes (basal myoepiythelial
markers like CK5,CK14,CK17and laminin. Overexpression P-Cadherin, Fascin ,
Caveolins 1&2 , alphabeta crystallin and epidermal growth factor receptor –EGFR
• A high histologic grade
• High rates of metastasis to the brain and lung.

17. Normal Breast Like
• 5-10% of breast carcinomas
• Clinical significance underdetermined
• Negative for CK5 and EGFR otherwise similar to basal like in expression of
various biomarkers
• Intermediate prognosis between luminal and basal and usually do not respond to
neoadjuvant chemotherapy

18. Breast Cancer Development, Growth, Survival and
Metastasis Involves Multiple Interrelated Pathways
Concurrent
targeting of
multiple
pathways
will likely be
optimal!!

19. Bidirectional talk (cross talk of Hormonal and Her2
pathways )

20. Summary of the major molecular subtypes
Eliyatkin N et al, Journal of Breast Health 2015; 11: 59-66

21. Clinical Applications of Genetic Assays
Vieira AF and Schmitt F (2018) An Update on Breast Cancer Multigene Prognostic Tests—Emergent
Clinical Biomarkers. Front. Med. 5:248.

22. Multigene assay
• Oncotype DX
• Mammaprint
• PAM50
• Breast Cancer Index
• Endopredict Index
• IHC4 score
• Next Generation Sequencing

23. Clinical trials implicated in the
development of multigene prognostic
signatures
Vieira AF and Schmitt F (2018) An Update on Breast Cancer Multigene Prognostic Tests—Emergent Clinical Biomarkers. Front. Med. 5:248.

24. Vieira AF and Schmitt F (2018) An Update on Breast Cancer Multigene Prognostic Tests—Emergent
Clinical Biomarkers. Front. Med. 5:248.

25. Therapeutic Targets

26. Hormonal pathways
• Estrogen signalling - therapeutic
success story
• SERMs, aromatose inhibitors and
ovarian ablation
• Highly effective and have a made a
significant impact on breast cancer
mortality and morbidity

27. Growth factor receptor pathways
• HER2 (EGFR 2 or Erb2 ) -
• HER2 amplification is associated with deregulation of G1/S phase cell cycle
control via up-regulation of cyclins D1, E, and cdk6, as well as p27 degradation
Trastuzumab-
• disrupts heterodimeric interaction of HER2 with other EGFR family members
• modulate host immunity, activating natural killer cells involved in
• antibody-dependent cellular cytotoxicity
• decrease tumor-associated microvessel density

28. Growth factor receptor pathways contd…..
• Lapatinib - inhibits tyrosine phosphorylation of both EGFR and HER 2 which in
turn inhibits the activation of proproliferativekinases ERK1/2 and AKT
• IGF – 1R - primary respose mediator for IGF .
• PI3-K Pathway – central signalling pathway downstream of tyrosine kinases and
regulates cell growth and proliferation
Rapamycin - m TOR inhibitors
Raf inhibitor - sorafenib

29. Angiogenesis
VEGFR 2 mediates most of the functions
• Bevacizumab - humanized monoclonal
antibody, First line metastatic setting
Multi targeted agents
• Sunitinib - VEGFR, PDGFR and c- kit
• Sorafenib - VEGFR, RAF kinase

30. Picture credits; clinical care options

31. Picture credits; clinical care options

32. Summary
The histological appearance of the tumors may not be sufficient to establish
the underlying complex genetic alterations and the biological events involved
in cancer development and progression
Defining more detailed biological characteristics to improve patient risk
stratification and to ensure the highest chance of benefit and the least toxicity
from a specific treatment modality