Breast cancer

Breast cancer happens when cells in the breast begin to grow out of control and can then invade nearby tissues or spread throughout the body. Large collections of this out of control tissue are called tumors. However, some tumors are not really cancer because they cannot spread or threaten someone's life. These are called benign tumors. The tumors that can spread throughout the body or invade nearby tissues are considered cancer and are called malignant tumors. Theoretically, any of the types of tissue in the breast can form a cancer, but usually it comes from either the ducts or the glands. Because it may take months to years for a tumor to get large enough to feel in the breast, we screen for tumors with mammograms, which can sometimes see disease before we can feel it.