Reproductive factors, age at maximum height, and risk of three histologic types of breast cancer

Numerous studies have evaluated the association between factors related to maturation and reproduction and breast cancer risk, but few have assessed how these factors are related to different histologic types of breast cancer among postmenopausal women. We used polytomous logistic regression to assess the effect of age at maximum height and reproductive factors on risk of invasive breast cancer by histologic type in three case groups (524 ductal, 324 lobular, and 196 ductal-lobular) and 469 controls enrolled in a population-based case-control study of women ages 55 to 74 years residing in the Seattle-Puget Sound region of Washington State (2000-2004). Histologic type was determined by a centralized tissue review for 83% of cases. Age at menarche and age at maximum height were inversely associated with risk of ductal-lobular carcinoma (P(trend) = 0.04 for both exposures) but not ductal or lobular carcinoma. Relative to nulliparous women, parous women had a 50% reduced risk of all histologic types of breast cancer. We observed similar increases in risk across histologic types associated with having a first live birth at ages > or = 30 years compared with ages < or = 19 years. Compared with parous women who never breast-fed, those who breast-fed had a reduced risk of ductal carcinoma (odds ratio, 0.7; 95% confidence interval, 0.5-0.9) but not lobular or ductal-lobular carcinoma. Further exploration of breast cancer risk by histology is merited to understand differences in the etiology of ductal, lobular, and ductal-lobular carcinoma.