Tumors of the hematopoietic and lymphoid tissues are a group of cancers that affect the cells of the immune system. These tumors can affect the bone marrow, lymph nodes, spleen, and other organs of the immune system. They can be benign or malignant, and can be caused by a variety of factors, including genetic mutations, environmental exposures, and viral infections. Treatment for these tumors may include chemotherapy, radiation therapy, and/or surgery.