Effect of reproductive factors and oral contraceptives on breast cancer risk in BRCA1/2 mutation carriers and noncarriers: results from a population-based study.
BACKGROUND
Multiparity and breast-feeding reduce breast cancer risk, whereas oral contraceptive use may slightly increase breast cancer risk in the general population. However, the effects of these factors in BRCA1 and BRCA2 mutation carriers are less clear.


METHODS
Case patients were 1,469 women from Los Angeles County ages 20 to 49 years with newly diagnosed breast cancer. Control subjects were 444 women without breast cancer, individually matched to a subset of cases on race, age, and neighborhood. BRCA1/2 genes were sequenced in the cases, and odds ratios of breast cancer associated with various reproductive and hormonal factors in BRCA1/2 mutation carriers and noncarriers were estimated using multivariable logistic regression.


RESULTS
Ninety-four women had a deleterious BRCA1 or BRCA2 mutation. Number of full-term pregnancies was inversely associated with breast cancer risk regardless of BRCA1/2 mutation status. Longer breast-feeding duration was protective among noncarriers but not among mutation carriers; however, this apparent effect modification was not statistically significant (P = 0.23). Neither oral contraceptive use overall nor the use of low-dose oral contraceptives was associated with an increased risk of breast cancer in any subgroup.


CONCLUSIONS
Our results suggest that parity protects against breast cancer in BRCA1/2 mutation carriers, whereas breast-feeding does not. Our data suggest no association between oral contraceptive use and breast cancer risk in BRCA1/2 mutation carriers. Further confirmation that currently available low-dose oral contraceptives do not increase breast cancer risk in carriers is important from a public health perspective given the high prevalence of oral contraceptive use in the United States.
Lee
Eunjung
E
Department of Preventive Medicine, Keck School of Medicine, University of Southern California/Norris Comprehensive Cancer Center, Room 4407, 1441 Eastlake Avenue, Los Angeles, CA 90089, USA.
Ma
Huiyan
H
McKean-Cowdin
Roberta
R
Van Den Berg
David
D
Bernstein
Leslie
L
Henderson
Brian E
BE
Ursin
Giske
G
D000328:Adult; D000704:Analysis of Variance; D001942:Breast Feeding; D001943:Breast Neoplasms / Q000139:chemically induced* / Q000453:epidemiology / Q000235:genetics*; D016022:Case-Control Studies; D016009:Chi-Square Distribution; D003278:Contraceptives, Oral, Hormonal / Q000008:administration & dosage* / Q000009:adverse effects; D004334:Drug Administration Schedule; D005260:Female; D019398:Genes, BRCA1; D024522:Genes, BRCA2; D006801:Humans; D016015:Logistic Models; D015141:Los Angeles / Q000453:epidemiology; D008875:Middle Aged; D009154:Mutation; D010298:Parity; D011247:Pregnancy; D012042:Registries; D018570:Risk Assessment; D012307:Risk Factors
D003278:Contraceptives, Oral, Hormonal