Spleen cancer. Gross specimen of a spleen showing a large lymphosarcoma, or non-Hodgkin's lymphoma (yellow), a cancer of lymphoid tissue. The lymphatic system is a major part of the immune system. The cancer weakens the immune system, making the patient susceptible to infections, and making normally harmless infections life threatening. The cancer can be treated by radiotherapy and chemotherapy, although the prognosis is generally poor by the time of diagnosis.