Smoldering Myeloma and MGUS: What's the Difference?

This page is for people told they have MGUS or smoldering myeloma, and for their families. It explains what these conditions are, how they are monitored, and when to get help sooner.

MGUS and smoldering myeloma are plasma cell conditions (plasma cells are immune cells in the bone marrow) that sit on the path before active multiple myeloma. Neither one is active myeloma.

In MGUS, abnormal plasma cells make up less than 10 percent of the bone marrow, and there is no cancer. They release a protein called M protein, which usually turns up by chance on a blood or urine test. According to the National Cancer Institute’s “Plasma Cell Neoplasms Treatment (PDQ),” in most people the M protein level stays steady and causes no trouble. But MGUS can become cancer, which is why the checks matter.

Smoldering myeloma sits between MGUS and active myeloma. NCI's term for it is smoldering multiple myeloma: myeloma that does not cause any signs or symptoms. It, too, is often found when a blood or urine test is done for another condition.

Testing may include blood and urine protein studies and serum free light chains. It also often includes bone marrow testing, imaging, and blood tests for kidney function, calcium, and hemoglobin.

Ask which tests are done and which are still pending. Blood counts, bone marrow testing, chromosome studies, molecular testing, and imaging can all matter here.

Teams look at the M protein level, the free light chain result, and how much of the marrow is made of plasma cells. Imaging results and other features count too. Ask which of yours are being tracked, and what a change in each would mean.

Two people with the same label can end up with different plans. Age, symptoms, blood counts, genetic changes, and kidney function all feed into it.

MGUS is monitored, not treated. Smoldering myeloma is often monitored too, though a high-risk case may lead to a specialist discussion or a clinical trial.

Waiting can feel wrong. Here it is the plan, not a delay. Monitoring is meant to catch a change early, so treatment starts when it is actually needed. Ask your team how often you will be checked, and which test results they are watching.

• Stage and spread do not mean the same thing in blood conditions as they do in solid tumors.
• A slow-moving condition is not always harmless. It still needs follow-up.
• Supportive care, infection prevention, and symptom control are part of care, not extras.

• What exact subtype do I have?
• Is it fast-growing or slow-growing?
• What genetic, chromosome, or molecular results matter?
• Do I need treatment now, or is observation reasonable?
• What symptoms or lab changes would make us act sooner?
• Is a clinical trial worth discussing?

Most people with MGUS or smoldering myeloma feel well. When they do progress, a new symptom is often the first sign. Report new symptoms. Do not wait for your next appointment.

• Call 911 or go to an emergency department if you have severe back pain along with new weakness or numbness in your legs, or trouble passing or holding urine. Pressure on the spinal cord is an emergency. Treating it early protects the ability to walk. Also go if a bone breaks after a minor bump or fall. Do not drive yourself.
• Call 911 or go to an emergency department if confusion comes on suddenly, is the first time the person has been confused for no known reason, is severe, or you are very hard to wake (MedlinePlus). Do not drive yourself.
• Call your care team right away, at any hour, if you have a temperature of 100.4°F (38°C) or higher or another sign of infection. Myeloma and its treatment can make infections more likely. Also call right away if you feel very thirsty, are urinating often, and become confused, drowsy, or sick to your stomach. That combination can mean a high calcium level in the blood.
• If you are getting chemotherapy or another marrow-suppressing drug, CDC says a fever during treatment is a medical emergency. Call your doctor immediately, at any hour. Keep the day and after-hours numbers nearby. If nobody answers, go to the emergency room or call 911.
• Call your care team within a day or two if you have new or worsening bone pain, especially in the back or ribs, new tiredness or shortness of breath, easy bruising or bleeding, or a clear drop in how much urine you pass.

• National Cancer Institute — Plasma Cell Neoplasms (Including Multiple Myeloma) Treatment (PDQ) – Patient Version
• MedlinePlus — Multiple Myeloma
• CDC — Preventing Infections: Fever

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