For a quick overview of the many different types of breast cancer, read this brief article.
Breast cancer is a malignant tumor that has developed from cells of the breast.
The disease occurs mostly in women, but does occur rarely in men. The remainder of this document refers only to breast cancer in women. A separate document on male breast cancer is also available from the American Cancer Society. Lymphatic vessels are similar to veins, except that they carry lymph instead of blood. Lymph is a clear fluid that contains tissue waste products and immune system cells that are on their way from areas of infection.