What Breast Cancer Is
Dr. Rob + Sources
Dr. Rob on Breast Cancer BiologyWhy early stage changes everything
Breast cancer starts in the cells of the ducts or lobules. Most are hormone-receptor-positive (ER/PR+), which is why hormones across a lifetime influence risk — and why anti-estrogen therapy works for many patients.
Stage at diagnosis is the single biggest driver of survival. Localized disease has 99%+ 5-year survival; once it spreads to distant organs that drops sharply. Screening exists to catch it before it spreads.
📊 Data sourcesACS Cancer Facts & FiguresNCI SEER Stat Facts
Breast cancer is a malignant growth that begins in breast tissue — most often in the milk ducts (ductal) or the milk-producing lobules (lobular). It can stay contained, invade nearby tissue, or spread (metastasize) to lymph nodes and distant organs. It is named for where it begins: breast cancer that spreads to bone is still breast cancer.
It is not one disease. Subtypes — hormone-receptor status (ER/PR), HER2 status, and triple-negative — behave differently and are treated differently. Though far less common, men can develop breast cancer too (about 1% of cases).
About 1 in 8 US women will be diagnosed in her lifetime.
ER/PR and HER2 status determine treatment — targeted therapy has transformed outcomes.
Localized breast cancer has 99%+ 5-year survival.
~1% of breast cancers occur in men — a lump should never be ignored.