Blood

Lymphoma is cancer of the lymphocytes and arises outside the bone marrow, in the lymph nodes, the spleen, or the lymphatic tissue of the gut. This disease typically causes enlargement of the lymph nodes and constitutional symptoms such as fever, sweats, and weight loss. Frequently, lymphoma invades the bone marrow, causing anemia, thrombocytopenia, and leukopenia. There exists a great number of subtypes of lymphoma that differ substantially in their clinical behavior, ranging from indolent or "low grade" lymphomas that may cause minimal symptoms to aggressive "high grade" lymphomas that run a stormy course and require urgent treatment. Lymphoma is treated with chemotherapy, sometimes combined with radiation therapy. Although some cases of lymphoma can be cured, these remain in the minority.

Multiple myeloma is a neoplastic disease affecting the antibody-producing cells, or plasma cells. Like other malignancies of the blood, the incidence of this condition increases with age; 98 percent of cases occur in patients older than forty years. In myeloma, malignant plasma cells accumulate in the bone marrow. These malignant cells produce great quantities of an antibody, known as a monoclonal paraprotein. This antibody is not produced in response to infection and is useless to the body. Indeed, the paraprotein may injure the kidney, and as malignant plasma cells accumulate, normal plasma cells, and other bone marrow cells, are suppressed and the production of normal antibodies is severely impaired. Anemia is also frequently present. In addition, the malignant cells secrete chemicals, known as cytokines, which cause the bones to lose calcium and weaken. Hence, patients with myeloma may experience fatigue, frequent infections, pain and fractures of bone, and kidney failure. No cure for multiple myeloma is known, although treatment with chemotherapy may temporarily reduce the burden of malignant cells and alleviate symptoms. Drugs that stimulate the bones to retain calcium have been proven effective in reducing bone loss and its complications.

The presence of a paraprotein is not sufficient to establish the diagnosis of myeloma. Indeed, monoclonal paraproteins are common in older adults, but usually occur in the absence of the accumulation of malignant plasma cells, anemia, bone destruction, and kidney damage characteristic of myeloma. These cases are referred to as "monoclonal gammopathy of unknown significance" (MGUS). Some cases of MGUS probably represent early myeloma, or a pre-malignant condition that leads to myeloma. In most cases, however, this condition remains entirely benign.