Colon cancer. Colonoscope (endoscope) view of a colonic cancer (lymphoma) in an 83 year-old female patient. A lymphoma is cancer of lymph tissue, here the ascending colon is showing ulceration and constriction due to the cancer. The lymphatic system is a network of nodes (glands) and ducts that carry lymph fluid around the body. This contains white blood cells that fight infection. Lymphoma causes proliferation of these cells, although they are not fully functional, and it severely compromises the working of the immune system. Surgery to remove the lymphoma discovered a second smaller lesion in the ileum, the last part of the small intestine.