Breastfeeding and Breast Cancer Risk in BRCA Mutation Carriers
Breastfeeding and Breast Cancer Risk in BRCA Mutation Carriers
Case and control subjects were similar with respect to year of birth, oral contraceptive use, age at last birth, smoking status and body mass index (BMI) at age 30 (Table 1). Cases with a BRCA1 mutation had a significantly earlier age at menarche than controls (13.09 years vs. 13.27 years; P = 0.003) and were less likely to have consumed alcohol (61% vs. 67%; P = 0.002). Although not significant, age at first birth (24.8 vs. 25.1; P = 0.08) and age at last birth (29.0 vs. 29.3; P = 0.06) were, on average, earlier in BRCA1 mutation carriers compared with controls. Hormone replacement therapy (HRT) use was significantly lower in both BRCA1 and BRCA2 cases versus controls (5% vs. 12%; P < 0.0001 and 10.7% vs. 16.5%; P = 0.02, respectively). Age at menarche, age at first birth, age at last birth, mean duration of breastfeeding and alcohol consumption did not differ between cases and controls with a BRCA2 mutation.
The mean duration of breastfeeding was shorter among the cases than the controls with a BRCA1 mutation (8.8 months vs. 10.4 months; P = 0.0009). There was a significant reduction in breast cancer risk with breastfeeding among women with a BRCA1 but not a BRCA2 mutation (Table 2). On average, BRCA1 cases breastfed for 1.6 fewer months than controls (8.8 vs. 10.4 months P = 0.0009). There was only a 0.5-month difference between cases and controls with a BRCA2 mutation (10.2 vs. 9.7 months P = 0.56). Among BRCA1 mutation carriers, breastfeeding for at least one year was associated with a 32% reduction in risk (OR = 0.68; 95% CI 0.52 to 0.91; P = 0.008); breastfeeding for two or more years conferred an even stronger reduction in risk (OR = 0.51; 95% CI 0.35 to 0.74; P = 0.0003). Each year of breastfeeding conferred a 19% reduction in risk. The effect of breastfeeding was present for women diagnosed at all ages. The reduction in risk associated with breastfeeding for one or more years compared with never breastfeeding was 44% for women with an age at breast cancer diagnosis of ≤ 39 (OR = 0.56; 95% CI 0.33 to 0.96), 54% for those with an age at diagnosis of 40 to 49 (OR = 0.46; 95% CI 0.26 to .81) and 69% for those with an age at diagnosis of ≥ 50 (OR = 0.31; 95% CI 0.07 to 1.30).
Among BRCA2 mutation carriers, there was no significant association between breastfeeding for at least one year and breast cancer risk (OR = 0.83; 95% CI 0.53 to 1.31; P = 0.43). There was no relationship following stratification by age at diagnosis. The risk estimates associated with breastfeeding for one or more years compared with never breastfeeding by age at diagnoses ≤ 39, 40 to 49 and ≥ 50 were 0.98 (95% CI 0.37 to 2.62), 1.41 (95% CI 0.59 to 3.43) and 0.91 (95% CI 0.24 to 3.43), respectively.
Results
Case and control subjects were similar with respect to year of birth, oral contraceptive use, age at last birth, smoking status and body mass index (BMI) at age 30 (Table 1). Cases with a BRCA1 mutation had a significantly earlier age at menarche than controls (13.09 years vs. 13.27 years; P = 0.003) and were less likely to have consumed alcohol (61% vs. 67%; P = 0.002). Although not significant, age at first birth (24.8 vs. 25.1; P = 0.08) and age at last birth (29.0 vs. 29.3; P = 0.06) were, on average, earlier in BRCA1 mutation carriers compared with controls. Hormone replacement therapy (HRT) use was significantly lower in both BRCA1 and BRCA2 cases versus controls (5% vs. 12%; P < 0.0001 and 10.7% vs. 16.5%; P = 0.02, respectively). Age at menarche, age at first birth, age at last birth, mean duration of breastfeeding and alcohol consumption did not differ between cases and controls with a BRCA2 mutation.
The mean duration of breastfeeding was shorter among the cases than the controls with a BRCA1 mutation (8.8 months vs. 10.4 months; P = 0.0009). There was a significant reduction in breast cancer risk with breastfeeding among women with a BRCA1 but not a BRCA2 mutation (Table 2). On average, BRCA1 cases breastfed for 1.6 fewer months than controls (8.8 vs. 10.4 months P = 0.0009). There was only a 0.5-month difference between cases and controls with a BRCA2 mutation (10.2 vs. 9.7 months P = 0.56). Among BRCA1 mutation carriers, breastfeeding for at least one year was associated with a 32% reduction in risk (OR = 0.68; 95% CI 0.52 to 0.91; P = 0.008); breastfeeding for two or more years conferred an even stronger reduction in risk (OR = 0.51; 95% CI 0.35 to 0.74; P = 0.0003). Each year of breastfeeding conferred a 19% reduction in risk. The effect of breastfeeding was present for women diagnosed at all ages. The reduction in risk associated with breastfeeding for one or more years compared with never breastfeeding was 44% for women with an age at breast cancer diagnosis of ≤ 39 (OR = 0.56; 95% CI 0.33 to 0.96), 54% for those with an age at diagnosis of 40 to 49 (OR = 0.46; 95% CI 0.26 to .81) and 69% for those with an age at diagnosis of ≥ 50 (OR = 0.31; 95% CI 0.07 to 1.30).
Among BRCA2 mutation carriers, there was no significant association between breastfeeding for at least one year and breast cancer risk (OR = 0.83; 95% CI 0.53 to 1.31; P = 0.43). There was no relationship following stratification by age at diagnosis. The risk estimates associated with breastfeeding for one or more years compared with never breastfeeding by age at diagnoses ≤ 39, 40 to 49 and ≥ 50 were 0.98 (95% CI 0.37 to 2.62), 1.41 (95% CI 0.59 to 3.43) and 0.91 (95% CI 0.24 to 3.43), respectively.
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