Since breast cancer may emerge both before and after menopause onset, relevant forms of the disease show marked biological and clinical differences. Intrinsic properties of mammary fat located in the vicinity of tumor, which play a definitive role in stromal-epithelial interactions, are an important factor of development of such differences. The DNA damage promoting hormonal (leptin and adiponectin production, aromatase activity) and progenotoxic. The properties of mammary fat such as formation of tumor necrosis factor, interleukin-6, nitric oxide, malonic aldehyde, macrophage/histiocyte infiltration and estrogen 4-hydroxylase expression, were studied in mammary fat tissue of 95 patients with receptor-positive or receptor-negative breast tumors (reproductive--25, menopausal--70). It was found that progenotoxic properties might somewhat predominate, as far as differences in parameters and pathways are concerned, both in menopausal and still cycling patients. Hence, progenotoxic damage which represents mammary fat tissue status is perhaps modified by a number of genetic and mitochondrial factors. It may exert unfavorable effect on the course of the disease within a fairly wide period.