Anthropometric factors and risk of molecular breast cancer subtypes among postmenopausal Norwegian women

Adult height and body weight are positively associated with breast cancer risk after menopause, but few studies have investigated these factors according to molecular breast cancer subtype. A total of 18,562 postmenopausal Norwegian women who were born between 1886 and 1928 were followed up for breast cancer incidence from the time (between 1963 and 1975) height and weight were measured until 2008. Immunohistochemical and in situ hybridization techniques were used to subtype 734 incident breast cancer cases into Luminal A, Luminal B [human epidermal growth factor receptor 2 (HER2-)], Luminal B (HER2+), HER2 subtype, basal-like phenotype (BP) and five-negative phenotype (5NP). We used Cox regression analysis to assess adult height and body mass index (BMI) in relation to risk of these subtypes. We found a positive association of height with risk of Luminal A breast cancer (ptrend , 0.004), but there was no clear association of height with any other subtype. BMI was positively associated with risk of all luminal breast cancer subtypes, including Luminal A (ptrend , 0.002), Luminal B (HER2-) (ptrend , 0.02), Luminal B (HER2+) (ptrend , 0.06), and also for the HER2 subtype (ptrend , 0.04), but BMI was not associated with risk of the BP or 5NP subtypes. Nonetheless, statistical tests for heterogeneity did not provide evidence that associations of height and BMI differed across breast cancer subtypes. This study of breast cancer risk among postmenopausal women suggests that height is positively associated with risk of Luminal A breast cancer. BMI is positively associated with risk of all luminal subtypes and for the HER2 subtype.