Breast Cancer develops when a group of cells within the breast tissue grow out of control and the old cells do not die as they should. These groups of cells form lumps or tumors. Breast tissue covers a large area extending from the collar bone and under the arm across to the breast bone in the centre of the chest. Each breast is made up of glands, ducts and fatty tissue.  Lobules are groups of glands that can produce milk. The ducts are a network of thin tubes that carry the milk from the lobules to the nipple. The fatty tissue surrounds the glands and ducts for protection.  Cancer cells may start in the ducts (ductal carcinoma) or in the lobules (lobular carcinoma). Ductal carcinoma is the most common type of breast cancer*.

*Source: Breast Cancer: Understanding your diagnosis. Canadian Cancer Society, 2007.

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            York Region Health Connection at 1 800-361-5653, TTY 1-866-252-9933