Breast cancer develops from cells in the breast, usually in the lobules or ducts, and can invade nearby healthy tissue and lymph nodes over time. The most common types are ductal carcinoma, which starts in the ducts, and lobular carcinoma, which starts in the lobes. Breast cancer is staged based on tumor size and spread, from Stage 0 (non-invasive) to Stage IV (metastasized to other parts of the body). Risk factors include family history, genetic factors like BRCA1/2 mutations, reproductive factors, and lifestyle factors. Treatment depends on the cancer type and stage, and may involve surgery, radiation, chemotherapy, hormone therapy, and targeted biotherapies.