Oral contraceptives and the risk of breast cancer in BRCA1 and BRCA2 carriers.

P Ghadirian1, MP Dubé,2, S Narod,2

1 Epidemiology Research Unit,Research Centre CHUM, Hôtel-Dieu, University of Montreal, 2 The Center for Research on Womens Health, University of Toronto, Canada.

Aim. Oral contraceptive use has been associated with a modest increase in the risk of breast cancer among young women. We studied the possible association between oral contraceptive use and breast cancer risk in carriers of breast cancer susceptibility genes, BRCA1 and BRCA2 Methods. We performed a case-control study of 941 women with BRCA1 or BRCA2 mutation diagnosed with breast cancer (cases) and an equal number of non-affected carrier women (controls) recruited from 11 countries. Cases and controls were matched on year of birth, country of residence, mutation (BRCA1 or BRCA2), and history of ovarian cancer. Information obtained from the questionnaire. Results. Ever use of oral contraceptives was associated with a modest and non-significant increase in breast cancer risk among BRCA carriers (OR=1,06; P=0.61). For each year of contraceptive use the relative risk rose by 1.0% (OR=1.01; P=0.18). The OR for 15 or more years of contraceptive use among BRCA1 carriers was 1.37; (P=0.28) and among BRCA2 carriers it was (1.27; P=0.60). The effect of oral contraceptives appeared to be greater for breast cancers diagnosed at an early age (P=0.36). A significant decrease in breast cancer risk was observed for women who first took a contraceptive after age 30, compared to non-users (OR=0.50; P=0.01). Conclusions. Short term use of oral contraceptives does not appear to increase the risk of breast cancer appreciably in carriers of BRCA mutations. Long-term use of oral contraceptives may increase the risk, in particular for early-onset breast cancer. However, late use may be protective.

KEY WORDS: Oral contraceptives, breast cancer, BRCA1 and BRCA2 carriers.

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Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Paris, France; February 9 - 12, 2002; in the section on Risk Assessment, Part 1.

This presentation was a winner in our poster contest and was recognized with the Symposium Presidents' Award for Scientific Excellence.