Breast cancer is the most frequent cancer in women and represents the second leading cause of cancer death among women after lung cancer. A common phenotypic abnormality of breast cancer cells is dysregulation of cell cycle control. The transformation of normal cell to a cancer cell appears to depend on mutation in genes that normally control cell cycle progression, thus leading to loss of the regulatory cell growth. We summarize here the molecular regulation of mammary carcinoma with regards to the most prominent oncogenes and tumor suppressor genes and their outcome in terms of cellular prognosis, and tumor development.