Breast cancer arises when cells in breast tissue acquire genetic changes that disrupt normal growth controls, allowing uncontrolled division and potential spread. It is among the most common cancers in women worldwide and risk increases with age. Hormonal factors, family history, inherited mutations such as in BRCA1 and BRCA2, reproductive history, and lifestyle factors like obesity and alcohol use can all influence risk, but most cases occur without a clear single cause.

Tumors are classified by where they start and by molecular features. Most begin in ducts or lobules. Key subtypes include hormone receptor positive cancers that respond to estrogen or progesterone, HER2 positive cancers driven by excess HER2 protein, and triple negative cancers that lack these targets and tend to behave more aggressively. These biological differences guide treatment choices and help predict outcomes.

Early detection is crucial. Mammography is the main screening tool, with ultrasound and MRI used in specific situations, especially in younger women or those at very high risk. Diagnosis is confirmed by biopsy, followed by laboratory tests that determine tumor type, grade, receptor status and sometimes genomic risk scores.

Treatment typically combines surgery, radiotherapy, systemic therapies such as chemotherapy, hormone therapy for receptor positive tumors, targeted drugs against HER2 and newer agents like CDK4/6 inhibitors and immunotherapies. Cure is often possible when cancer is found early, and survival has improved substantially as a result of screening, better systemic treatments and more precise tailoring of therapy to each tumor’s biology. Long term follow up focuses on recurrence monitoring and management of treatment side effects.