Multiple Myeloma Biomarkers
M protein — the abnormal antibody secreted by myeloma cells — is the central biomarker of multiple myeloma: its level in blood or urine directly measures disease activity and whether treatment is working.
Reviewed by XpertPatient Medical Advisory · Updated June 2026 · Sources: NCI · ACS · ASCO · NIH/PMC
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What is a biomarker?
A biomarker in multiple myeloma is usually an abnormal protein made by myeloma cells — measurable in your blood or urine. Unlike most cancers, myeloma is tracked primarily through blood and urine tests rather than imaging scans.
Myeloma cells produce an abnormal antibody called M protein. Measuring M protein is your doctor’s main window into the disease — how active it is and whether treatment is working. As treatment works, M protein falls. If it rises again, the myeloma may be coming back.
What this means for you: Think of your M protein level as your disease thermometer. Your doctor checks it regularly throughout treatment to see if the treatment is working.
The Tests Your Doctor Orders
🔍 Is there an abnormal antibody in your blood or urine?
M protein is made by myeloma cells. In a healthy person, many different antibodies are produced. In myeloma, one type produces one identical antibody in excess. Measuring M protein by blood (SPEP) or urine test shows exactly how active the myeloma is.
🔍 Are protein fragments from myeloma cells measurable in your blood?
Free light chains are fragments of the abnormal antibody. The ratio of kappa to lambda chains — and how the levels change — helps track disease activity and response to treatment.
🔍 Does this protein level indicate how advanced the disease is?
Higher levels mean more disease burden. Along with albumin and LDH, it’s used in the ISS staging system to classify myeloma as Stage I, II, or III.
Watch & Learn
Common Questions
Multiple Myeloma Biomarkers — Your Questions Answered
How is M protein measured?
By a blood test called SPEP (serum protein electrophoresis) that identifies the abnormal spike. Urine protein electrophoresis (UPEP) checks for M protein in urine. Both are done regularly throughout treatment.
What does complete response mean in myeloma?
M protein is no longer detectable and bone marrow biopsy shows less than 5% plasma cells. Achieving a deep response is strongly linked to better long-term outcomes.
What is MRD testing?
Minimal residual disease (MRD) testing uses ultra-sensitive methods to detect myeloma even when standard tests show nothing. Achieving MRD-negative status is increasingly the treatment goal in clinical trials.
What are high-risk cytogenetics in myeloma?
Specific chromosome changes — found by FISH testing on bone marrow — that signal more aggressive myeloma. Patients with high-risk features often receive more intensive treatment or are prioritized for clinical trials.
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