What is the definition or description of: breast cancer?

Seel below: The breast is both a male and female organ. However its main function is in the delivery of milk to the newborn. Breast cancer occurs 95% of the time in women and 5% of the time in men. It is treated the same regardless of which sex it appears in. It comes in two forms invasive and non-invasive; distinction is important as it helps define treatment.

Tumor in the breast: Breast cancer starts when normal breast cells get damaged and keep growing, forming a lump and sometimes moving to other parts of the body. Normal breast cells grow and divide at different times in life, but then stop. Breast cancer cells never stop. They don't have an "off"switch. So they make more cells that also keep growing. Treatment removes the cells (surgery) and makes them stop (chemo).