Clinical Aspects of Hereditary Breast Cancer

Sammanfattning: A positive family history of breast cancer (BC) is one of the strongest predictors of the disease. Two major BC susceptibility genes, BRCA1 and BRCA2 were identified about a decade ago. In this thesis, studies of different biological. clinical and epidemiological aspects of hereditary BC are presented. In the first paper data on the expression of steroid hormone receptors in hereditary BC are presented. We confirm previously published data regarding the paucity of estrogen and progesterone receptors in BRCA1-associated BC, and report new findings in BRCA2-associated tumours and cases with an unidentified hereditary factor. Hormone receptor levels in these two groups do not differ significantly from each other or from an age-matched control population unselected for family history. The second paper is a cohort study of cancer incidence in relatives of BRCA1 and BRCA2 germline mutation carriers. Other cancers than BC and ovarian cancer do not appear to be greatly increased and require specific follow-up in carriers. The third study is a retrospective case-control study on the prognosis and clinical presentation of BRCA2-associated BC. BC in families with an identified BRCA2 mutation seemed to present at a more advanced stage at diagnosis compared with age and year of diagnoses matched controls. This translated into an increased risk to die from BC in this group, but overall survival was not significantly decreased. The fourth study is a population-based study of family history and BRCA1 and BRCA2 mutations in BC cases below the age of 41. A positive family history was very frequent in this group of young BC patients. About one-third of them had a family history including at least one first- or second-degree relative with BC. A positive BRCA1-mutation status was observed in 6.8% of the cases, and BRCA2-mutations were seen in 2.1% of the in women. BRCA1 and BRCA2 mutations were more prevalent in younger women, in women with a positive family history including at least one first-degree relative with breast or ovarian cancer, and in women that had already or did develop a bilateral BC during a median follow-up of 5.5 years. In the fifth study relative and cumulative cancer incidence in the first-degree relatives of the woman of the previous study were calculated and compared with the population. The BC risk was still increased in first-degree relatives of women with early-onset BC (below the age of 41) when BRCA-mutation carriers were excluded, in addition an association with prostate cancer was suggested. The risk of prostate cancer did only appear to be increased in relatives of women with BC below the age of 36. Furthermore, cumulative BC incidences were calculated for women with different hereditary backgrounds.