Colon cancer is a disease in which the normal cells in the lining of the colon begin to change in a way that causes them to grow uncontrollably and form a mass of cells, called a tumor. If a tumor is large enough, it can interfere with the normal function of the colon, such as digesting food and passing waste. The colon is part of the large intestine; the rectum is the last few inches of the colon, and the treatment of tumors in this area may differ from other areas of the colon.
Staging is a way of describing the cancer, such as its size, and whether or where the cancer has spread. Cancer may spread through the blood or lymphatic system. The lymphatic system is part of the immune system and drains fluid from body tissues through a series of tubes. Lymphatic fluid is filtered in small, bean-shaped organs called lymph nodes. When cancer cells travel in the lymphatic system, they become trapped in the lymph nodes. Stage II colon cancer means that the cancer has spread through the wall of the colon and may have spread to nearby tissues or organs, but has not spread to the nearby lymph nodes.