Higher parity and shorter breastfeeding duration

Abstract

BACKGROUND: The combination of increased parity and shorter breastfeeding duration might increase the odds of the least differentiated triple‐negative breast cancer (BC) phenotype, theoretically because an expanded progenitor cell population from each pregnancy would incompletely differentiate postpartum. METHODS: Subjects consisted of a consecutive case series of 2473 women treated for invasive breast cancer between 2001 and 2006. Breast cancer phenotype (triple‐negative BC, vs non–triple‐negative BC) was compared with reproductive and demographic information. Odds ratios (OR) with 95% confidence intervals (CIs) for the association of breastfeeding duration (months per child) and parity with triple‐negative BC were calculated after adjusting for ethnicity, age at menarche, family history, and age at diagnosis. RESULTS: Compared with non–triple‐negative BC, triple‐negative BC was associated with shorter duration of breastfeeding per child (OR, 0.93; 95% CI, 0.90‐0.97) and with higher parity (OR, 1.12; 95% CI, 1.06‐1.20). By using multivariate logistic regression, triple‐negative BC was independently associated with higher parity (OR, 2.76 [95% CI, 1.86‐4.08] if ≥3 live births; OR, 1.89 [95% CI, 1.30‐2.74] if ≤2 live births vs nulliparae), breastfeeding duration (OR, 0.55 [95% CI, 0.41‐0.74] if >2 mo/child and OR, 0.58 [95% CI, 0.42‐0.82] if ≤2 mo/child vs none), African American ethnicity (OR, 2.10; 95% CI, 1.52‐2.92), and younger age at diagnosis (OR, 3.02 [95% CI, 2.03‐4.47] if ≤40 years vs >60 years). CONCLUSIONS: Among women with invasive breast cancer, higher parity and the absence or short duration of breastfeeding were independently associated with triple‐negative BC. Any duration of breastfeeding was found to be associated with lower probability of triple‐negative BC, and the odds of this phenotype decreased with increasing duration of breastfeeding. Cancer 2010. © 2010 American Cancer Society.