This document summarizes information about breast cancer including its incidence, risk factors, classification, diagnosis, staging, prognosis, and treatment. Breast cancer begins in the breast tissue and may start in the ducts or lobes. It accounts for 20% of female cancer deaths and is most common above age 50. Risk factors include genetics, hormonal factors, precancerous lesions, dietary/environmental factors, and previous breast cancer. Diagnosis involves clinical examination, radiology like mammography and biopsy. Staging uses the TNM system to describe tumor size, lymph node involvement and metastasis. Treatment depends on stage and may involve surgery, chemotherapy, radiation, and hormone therapy.