WebMD: Non-Hodgkin's lymphoma
Non-Hodgkin's lymphoma (NHL) is cancer of the cells of the lymphatic system. In non-Hodgkin's lymphoma, cells in the lymphatic system divide and grow without order or control, or old cells do not die as cells normally do. Non-Hodgkin's lymphoma can start almost anywhere in the body. It may occur in a single lymph node, in a group of lymph nodes, or in an organ such as the spleen. Non-Hodgkin's lymphoma can spread to almost any part of the body, including the liver, bone marrow, and spleen.
Over time, lymphoma cells replace the normal cells in the bone marrow. This causes bleeding problems and infections. As the lymphoma cells spread, the body becomes less and less able to produce blood cells that carry oxygen to other tissues or to protect itself from infection.
Non-Hodgkin's lymphoma is different from Hodgkin's lymphoma and occurs about eight times more often.
Good luck to Lester recovering from this. It would be really crappy for such a young talent to be derailed by something like this.