Words to know: MGUS and smoldering myeloma
- MGUS
- Monoclonal gammopathy of undetermined significance. A small amount of M-protein in the blood with no harm to the body. It is not cancer.
- Smoldering myeloma
- A stage between MGUS and active myeloma. There are more abnormal plasma cells but no organ damage.
- Plasma cell
- A white blood cell in the bone marrow that makes antibodies to fight infection.
- Bone marrow
- The soft tissue inside bones where blood cells are made.
- M-protein
- The abnormal antibody made by a group of identical plasma cells. Also called monoclonal protein or M-spike.
- Monoclonal
- Coming from one cell that made many copies of itself.
- Light chains
- Small pieces of antibody protein. There are two kinds: kappa and lambda.
- Free light chain ratio
- A comparison of kappa and lambda light chains in the blood. An abnormal ratio can mean higher risk.
- Immunofixation
- A test that shows the exact type of M-protein.
- SPEP
- Serum protein electrophoresis. A blood test that finds and measures the M-protein.
- Progression
- When a condition changes or gets worse, such as MGUS turning into myeloma.
- Active monitoring
- Regular tests and visits instead of treatment, to catch any change early. Also called watch and wait.
- Risk group
- An estimate of how likely a condition is to progress, based on lab and test results.
- 20-2-20
- A tool that sorts smoldering myeloma into low, intermediate, or high risk using plasma cell percent, M-protein level, and light chain ratio.
- CRAB
- Signs of myeloma damage: high calcium, kidney problems, anemia, and bone damage.
- Bone marrow biopsy
- Taking a small sample of marrow, usually from the hip bone, to look at it under a microscope.
- FISH
- A lab test that looks for chromosome changes in plasma cells.
- Immunoparesis
- When healthy antibody levels are lower than normal.
- Daratumumab
- An antibody medicine that targets CD38 on plasma cells. It is approved for high-risk smoldering myeloma and for myeloma.
- Lenalidomide
- A pill that helps the immune system fight abnormal plasma cells.
- MGRS
- Monoclonal gammopathy of renal significance. A small plasma cell group whose protein harms the kidneys.
- Waldenstrom macroglobulinemia
- A slow-growing lymphoma that makes IgM protein. IgM MGUS can rarely turn into it.
- AL amyloidosis
- A related condition where light chains build up in organs and harm them.
- Hematologist
- A doctor who specializes in blood and bone marrow conditions.
Last updated: 2026-10-27. Medically reviewed by Veli Bakalov, MD, medical oncologist (October 2026). General education from Step by Step, the patient portal of HemeOncBuddy.