Breast cancer and genetics

Winter 2011

Macmillan Cancer Genetics Counsellor Karen Bailey discusses the implications of the BRCA1 and BRCA2 gene mutations.

Many factors influence a person’s heath such as the environment, their lifestyle, hormonal factors and, as is becoming increasingly apparent, genetic factors.^[1] Discussion about genetics and cancer, particularly breast cancer, is becoming more common.

Increasingly, women are questioning their diagnosis and family history, and expressing concerns about whether their cancer, or the cancers in their family, are likely to be genetic.

Predisposing genes

Familial clustering of breast cancer was recognised in ancient times. However, it wasn’t until studies were carried out in families with an excess of young, onset breast cancer and ovarian cancer, then in families with male and female breast cancers, that two major high-risk predisposing genes, BRCA1 and BRCA2, were identified in 1994–1995.^[2-4]

It is estimated that only 5–10% of all breast cancers are caused by an inherited mutation. BRCA1 and BRCA2 mutations are inherited in an autosomal dominant manner, which means that if a person has a mutation present in the gene, their offspring have a 50% chance of inheriting it.^{[5-6, 2]} Women who have a mutation in either of these genes have a 50–85% lifetime risk of developing breast cancer and a 10–40% lifetime risk of developing ovarian cancer.^[7] The presence of either one of these mutations also carries an increased risk of a second breast cancer.^[8]

Familial risk

Women who may have a higher risk of familial breast cancer include those who have a close relative diagnosed at a young age, or women with two or more close relatives on the same side of the family that have been affected. A gene mutation can also be passed down through the father’s side of the family and sometimes the medical history of both sides of the family can be significant.

There are also implications for men, such as an increased risk of developing prostate cancer at a younger age and male breast cancer, particularly in the presence of a BRCA2 mutation. Other cancers are also associated with these genes.

Genetic services

Specialist cancer genetics services and genetic counselling provide eligible individuals with information about the chance of their cancer being hereditary, or their risk of developing cancer, based on an assessment of their family history.

Specific genetic counselling can also affect the emotional adjustment of high-risk women, who often bear a great psychological burden because of their familial experiences of breast cancer and possibly high bereavement rates.^[9] In addition, genetic counselling and support following the disclosure of a diagnostic or predictive result is available to help women address future concerns, ensure they receive up-to-date information to make informed choices, and continue to be medically and psychologically supported.

It’s important to remember that genetic information carries implications not just for the woman involved, but also for her family, some of whom may not want such information.

More information

OPERA| is Macmillan’s self-assessment tool for people worried about their risk of getting breast and/or ovarian cancer.  

References

1. Skirton H, Patch C. Genetics for the Health Sciences: A handbook for clinical practice. 2009. 2nd Edition. Scion Publishing Ltd., Oxfordshire.

2. Haites N, Gregory H in Morrison PJ, Hodgson SV, Haites NE (Eds). Familial Breast and Ovarian Cancer: Genetics, screening and management. 2002. Cambridge University Press, Cambridge.

3. Meijers-Heijboer H. Breast cancer: Predisposing Genes and their Clinical Implications. 2002. Riddderprint offsetdrukkerij b.v., Ridderkerk.

4. Pritchard DJ, Korf BR. Medical Genetics at a Glance. 2003. Blackwell Science Ltd., Oxford.

5. Claus EB, Schildkraut JM, Thompson WD, Risch NT. The genetic attributable risk of breast and ovarian cancer|. Cancer. 1996. 77; 2318–2324.

6. Blackwood MA, Webber BL. BRCA1 and BRCA2: From molecular genetics to clinical medicine|. Journal of Clinical Oncology. 1998. 16; 1969–1977.

7. McGillivray BC. Management of familial breast and ovarian cancer in North America. Chapter 8b in Lalloo F, Kerr B, Friedman J, Evans G (eds). Risk Assessment and Management in Cancer Genetics. 2005. Oxford University Press, Oxford.

8. Narod SA, Offit K. Prevention and management of hereditary breast cancer|. Journal of Clinical Oncology. 2005. 23; 1656–1663.

9. Lloyd S, Watson M, Waites B, Meyer L, Eeles R, Ebbs S, Tylee A. Familial breast cancer: a controlled study of risk perception, psychological morbidity and health beliefs in women attending for genetic counselling|. British Journal of Cancer. 1996. 74 482–487.