What is lymphoma? Lymphoma is a malignant disease of lymphocytes, also known by some as lymph cancer. Because lymphatic tissue is all over the body, lymphoma can occur in any part of the body. It commonly occurs in the lymph nodes, tonsils, and spleen and may involve the bone marrow. Lymphoma can be divided into two major categories: Hodgkin's lymphoma and non-Hodgkin's lymphoma. It can occur at all ages, with peak incidence between 45-60 years old.