Prolonged exposure to estrogens was found to be a risk factor for breast cancer. The molecular mechanism has been suggested to be the binding of estrogen receptors in mammary tissue, which promotes the proliferation of breast tissue. Different biomarkers mapping estrogen receptor alpha (ESR1) have been associated with breast cancer risk, although the size of the effect is not consistent among different reports. Variation in the estrogen receptor gene PvuII has been associated with an increased risk of developing breast cancer. However, some studies suggest that its effect might be constrained to a definite subgroup of patients.In this study the involvement of PvuII in breast cancer was analyzed in an independent sample of 444 unrelated breast cancer cases and 704 controls of Spanish origin. A case-control comparison was performed and the genotype distributions examined according to different tumor and population parameters.A trend towards association was observed in adjusted case-control association analysis (p=0.07). PvuII was associated with the familial forms of breast cancer (OR=3.81, p=0.02). T allele frequency was higher among patients with highly differentiated tumors (p=0.02), positive for steroid receptors (p=0.06), and negative for p53 (p=0.02). However, the PvuII genetic background did not affect disease-free survival time (p=0.65).The PvuII T allele may be a germline risk factor for familial forms of breast cancer and is associated with a specific subset of immunohistochemical tumor phenotype.