Breast cancer is a malignant tumor that begins in the cells of the breast. A malignant tumor is a kind of cancer cell that can develop into surrounding tissues or spread to reserved areas of the body. This kind of disease occurs approximately in women.Breast cancers take place in any place in the breast, but mainly are found in the upper outer quadrant, where most breast tissues are found. Normally breast cancer starts in the cells of the lobules, which are the milk-producing glands. Less commonly, breast cancer can start in the stromal tissues, which involve the fatty as well as the fibrous connective tissue of the breast.