Pooled analysis of four prospective studies of plasma prolactin levels and risk of postmenopausal breast cancer

Prolactin, a hormone produced by the pituitary gland, regulates breast development and may contribute to breast cancer etiology. A pooled analysis of four prospective cohort studies included 8,279 postmenopausal women, of whom 3,442 were diagnosed with invasive breast cancer after enrollment. Prolactin concentrations were measured for all study participants in plasma samples collected when all women were postmenopausal and before any breast cancer diagnosis. Higher plasma prolactin concentrations were positively associated with postmenopausal breast cancer risk (> 13,2 ng/ml versus < 7.9 ng/ml : OR 1.20; p for trend < 0.001). Associations were primarily observed in current users of postmenopausal hormones at blood draw (> 13.2 ng/ml versus < 7.9 ng/ml: current users OR 1.58; p for trend <0.001; non-current users 1.08; p for trend =0.11). The authors conclude that prolactin may be a risk factor for postmenopausal breast cancer, particularly in the context of postmenopausal hormone use.