Breast cancer is a heterogeneous disease associated with diverse
biological behaviours and clinical outcome. Although some molecular subgroups of
breast cancer have a targeted
therapy, the most aggressive tumours still lack a molecular target. Despite
vitamin D being classically associated with the physiological role of
calcium regulation and
phosphate transport in bone metabolism, several studies have demonstrated a wide range of functions for this
hormone, which are particularly important in the field of
cancer. The mechanisms underlying the protective actions of
vitamin D in
cancer development are only sparsely understood, but evidence shows that
vitamin D participates in cell growth regulation, apoptosis and cell differentiation. In addition, it has been implicated in the suppression of
cancer cell invasion, angiogenesis and
metastasis. Most of
vitamin D biological actions are mediated by the
vitamin D receptor and the synthesis and catabolism of this
hormone are regulated by the
enzymes CYP27B1 and
CYP24A1. In the present review we highlight research data concerning the function of this
hormone in the mammary gland, with a special focus on breast
carcinogenesis. Hence, and although the available data are controversial, we consider not only updated information on the epidemiology of
vitamin D in
breast cancer and its potential value as a therapeutic agent or prophylactic (with an emphasis on molecular mechanisms and effectors of
vitamin D action), but include data on its role in other stages of
breast cancer progression as well. Accordingly, we review data on the influence of
vitamin D in the development of normal breast and the expression of
vitamin D-related
proteins (VDR,
CYP27B1 and CYP24A21) in benign mammary lesions and
ductal carcinomas in situ.