Recent progress in biological research and in particular in molecular biology has contributed to better understanding of oncogenesis. Hormone-related cancers share a unique mechanism of carcinogenesis, mainly because exogenous and endogenous hormones drive cell proliferation in these tumors. As a result of increased proliferation, random gene alterations can accumulate. Unfortunately, most of the genes regulated by hormones are currently unknown. Finally, growing number of genetic errors creates a malignant phenotype. This review presents current knowledge about the interrelations between hormones and hormone-related cancers with breast cancer as an example.