Little is known about the effects of endogenous protein hormones as well as estrogen-like endocrine disruptors on breast cancer cell responsiveness to DNA-damaging drugs.Prolactin (PRL) is a protein hormone whose major target is the breast where it acts as a mitogen and a survival factor.Bisphenol A (BPA) is a monomer of polycarbonate plastics which is abundant in the environment, is detectable at nM levels in serum from most tested individuals, and affects both reproductive and non-reproductive functions, including carcinogenesis.