MGUS and smoldering myeloma: Full guide

What are MGUS and smoldering myeloma?

MGUS stands for monoclonal gammopathy of undetermined significance. It is a long name for a common finding. It means a blood test found a small amount of an abnormal protein called M-protein (monoclonal protein). This protein comes from a small group of plasma cells in the bone marrow. Plasma cells are white blood cells that normally make antibodies to fight infection.

In MGUS, the group of abnormal plasma cells is small, and it is not causing harm. MGUS is not cancer. It usually causes no symptoms and is most often found by chance, when blood tests are done for another reason. About 3 in 100 people over age 50 have MGUS, and it becomes more common with age. It is about twice as common in Black Americans.

Smoldering myeloma is a middle step between MGUS and active multiple myeloma. There are more abnormal plasma cells or more M-protein than in MGUS. But there is still no damage to the bones, kidneys, or blood counts. Most people with smoldering myeloma also feel well.

MGUS turns into myeloma or a related condition in only about 1 in 100 people each year. Most people with MGUS never have a problem from it. Smoldering myeloma is more likely to change into active myeloma, especially in the first few years, so it is watched more closely.

The main goal is to watch over time with regular blood tests. This way, any change can be found early, before it causes harm. A few people with high-risk smoldering myeloma may be offered treatment to delay active myeloma.

Types and related conditions

Non-IgM MGUS (IgG or IgA)

The most common type. The M-protein is an IgG or IgA antibody. If it ever progresses, it most often turns into multiple myeloma, or rarely AL amyloidosis.

IgM MGUS

The M-protein is an IgM antibody. If it progresses, it more often turns into Waldenstrom macroglobulinemia or another slow-growing lymphoma, rather than myeloma.

Light chain MGUS

The plasma cells make only a small piece of antibody called a light chain, with no full M-protein. It is found with the free light chain blood test. It can rarely progress to light chain myeloma or AL amyloidosis.

Smoldering myeloma

More M-protein (3 or more in blood tests) or more plasma cells in the bone marrow (10 to 60 out of 100 cells) than MGUS, but no damage to organs. It is watched closely, and some people at high risk are offered treatment.

Active multiple myeloma

Myeloma that is causing damage, or is very likely to soon. Signs include high calcium, kidney problems, anemia, or bone damage. This needs treatment. See our multiple myeloma guide.

MGRS (monoclonal gammopathy of renal significance)

A small plasma cell group whose protein damages the kidneys, even though it is not cancer. A kidney biopsy is often needed. Because of the kidney harm, it is treated, often with medicines used for myeloma.

MGUS of neurologic significance

Sometimes the M-protein harms nerves, causing numbness, tingling, or weakness in the feet and hands. This is more common with IgM MGUS. A rare condition called POEMS syndrome also affects nerves. A neurologist and hematologist work together on these.

AL amyloidosis

A related condition where light chains fold the wrong way and build up in organs like the heart and kidneys. It needs treatment. See our AL amyloidosis guide.

Tests you may have

Serum protein electrophoresis (SPEP)

A blood test that finds the M-protein and measures how much there is. This number is followed over time to see if it is stable.

Immunofixation

A blood test that tells which type of M-protein you have, such as IgG, IgA, or IgM, and which light chain (kappa or lambda).

Serum free light chains

A blood test that measures kappa and lambda light chains and the ratio between them. An abnormal ratio can mean a higher chance of progression.

Blood counts and chemistry tests

A complete blood count checks for anemia (low red blood cells). Other blood tests check calcium and how well your kidneys work. Normal results help show there is no damage.

Urine tests

A urine sample, or urine collected over 24 hours, can look for M-protein, light chains, and protein leaking from the kidneys.

Bone marrow biopsy

A small sample of bone marrow is taken from the back of the hip bone with a needle, after numbing medicine. It counts the plasma cells and checks them for gene changes. Many people with low-risk MGUS do not need one. It is usually done for smoldering myeloma or higher-risk MGUS.

Imaging scans

A low-dose CT scan of the whole body, a PET-CT, or an MRI looks for early bone damage. Smoldering myeloma usually needs one of these. MRI can find small spots that other scans miss.

Heart and kidney checks for amyloidosis

If you have symptoms or abnormal light chains, your care team may check heart blood tests (NT-proBNP and troponin) and protein in the urine. These help rule out AL amyloidosis.

Risk groups and what they mean

MGUS and smoldering myeloma are not staged like cancers. Instead, doctors sort people into risk groups. A risk group gives an idea of how likely the condition is to change into myeloma or a related disease over time. It helps decide how often you need tests.

For MGUS, doctors look at 3 things: the M-protein level (1.5 or higher is a risk factor), the type of protein (anything other than IgG is a risk factor), and the free light chain ratio (abnormal is a risk factor). Having none of these means low risk.

For smoldering myeloma, a common tool is called 20-2-20. It looks at more than 20 percent plasma cells in the marrow, an M-protein over 2, and a light chain ratio over 20. Some newer tools also add gene test results. A risk group is an estimate, not a promise. Many people even in higher-risk groups stay stable for years.

Low-risk MGUS

None of the 3 risk factors. The chance of progression is very low, about 5 in 100 over 20 years. Follow-up tests can be spaced out.

Intermediate-risk MGUS

One or two risk factors. The chance of progression is higher but still small for most people. Tests are usually done about once a year.

High-risk MGUS

All 3 risk factors. Closer follow-up is needed, and a bone marrow test is often done.

Low-risk smoldering myeloma

None of the 20-2-20 factors. About 1 in 20 people progress within 2 years. Close watching is the usual plan.

Intermediate-risk smoldering myeloma

One of the 20-2-20 factors. About 1 in 5 people progress within 2 years. Watching closely is usual, and a clinical trial may be an option.

High-risk smoldering myeloma

Two or more factors. About 4 in 10 people progress within 2 years. Treatment with daratumumab or a clinical trial may be offered, or close watching.

When it counts as active myeloma

Some findings mean active myeloma even without symptoms: 60 percent or more plasma cells in the marrow, a very high light chain ratio (100 or more), or more than one bone spot on MRI. These are treated as myeloma.

Lab tests and risk features

A few lab results help your care team understand your risk. The trend over time often matters more than a single number. A slowly rising M-protein or worsening blood count can be a sign to look more closely.

Ask your care team which risk features you have, and what would make them change your follow-up plan.

M-protein level

How much abnormal protein is in your blood. A higher level, or one that keeps rising, means a higher chance of progression.

Type of M-protein

IgG has the lowest risk. IgA and IgM carry a bit more. IgM points more toward lymphoma than myeloma.

Free light chain ratio

Compares kappa and lambda light chains. A very abnormal ratio means more risk. A ratio of 100 or more, with a high involved light chain, counts as active myeloma.

Bone marrow plasma cell percent

How many marrow cells are plasma cells. MGUS is under 10 percent. Smoldering myeloma is 10 to 60 percent. Higher numbers mean more risk.

FISH (gene test on marrow)

Looks for chromosome changes in the plasma cells, such as t(4;14), t(14;16), a missing piece of chromosome 17, or extra copies of 1q. Some of these raise the risk in smoldering myeloma.

Low normal antibodies (immunoparesis)

When the other, healthy antibody levels drop, it can be a sign the abnormal cells are crowding out normal ones. This adds risk.

Evolving pattern

An M-protein or light chain level that rises steadily over the first year or two is linked to a higher chance of progression.

Hemoglobin, calcium, and creatinine

These track signs of damage: anemia, high calcium, and kidney problems. New changes should be checked quickly.

NT-proBNP and urine albumin

Screening tests for AL amyloidosis, a related condition. They are often checked if you have light chain MGUS, abnormal light chains, or symptoms like swelling or shortness of breath.

Main treatments and follow-up

Watching closely (active monitoring)

MGUS is not treated. Most smoldering myeloma is not treated either. You have regular blood tests, and sometimes scans, to catch any change early. This is a real plan, not doing nothing.

Follow-up for low-risk MGUS

Usually a repeat blood test about 6 months after diagnosis. If it is stable, many people then need tests only every 2 to 3 years, or when new symptoms appear.

Follow-up for higher-risk MGUS

A repeat test at about 6 months, then usually once a year for life. Your care team may do it more often if numbers change.

Follow-up for smoldering myeloma

Blood and urine tests every 2 to 3 months at first, since the first few years are when changes are most likely. If things stay stable, tests may be spaced out over time. Imaging, often an MRI or low-dose CT, is usually repeated at least once a year, or sooner if numbers rise.

Daratumumab for high-risk smoldering myeloma

Daratumumab is an antibody given as a shot under the skin. It targets a protein called CD38 on plasma cells. In the AQUILA trial it delayed active myeloma and helped people live longer. It is now FDA approved for high-risk smoldering myeloma and given for up to 3 years.

Lenalidomide

Lenalidomide is a pill that helps the immune system fight abnormal plasma cells. Studies showed it can delay active myeloma in higher-risk smoldering myeloma. Some doctors offer it, but it is not FDA approved for this use.

Clinical trials

Many trials study whether early treatment can prevent or delay myeloma. Some test newer drugs and combinations for high-risk smoldering myeloma. Ask your care team if one fits you.

Treatment for MGRS or nerve damage

When the protein harms the kidneys or nerves, the abnormal cells are treated even though the clone is small. Medicines are often the same ones used for myeloma or lymphoma, chosen by protein type.

Bone health

MGUS is linked to a slightly higher risk of thin bones and breaks. Your care team may suggest a bone density scan, calcium, vitamin D, exercise, and sometimes bone-strengthening medicine.

Starting myeloma treatment

If smoldering myeloma changes to active myeloma, treatment starts. Finding it early through regular tests means it can often be treated before serious damage. See our multiple myeloma guide.

Side effects and what helps

Worry while watching

Living with "wait and watch" can be stressful. Some people feel anxious before each blood test. Talking with your care team, writing down questions, and joining a support group can help. Counseling is a good option too.

Bone marrow biopsy discomfort

The biopsy can cause brief pressure or pain. Numbing medicine is used, and some centers offer mild sedation. The area may be sore for a few days. Call if you have bleeding that will not stop or signs of infection.

Injection reactions from daratumumab

Some people get chills, a stuffy nose, cough, or itching, mostly with the first shot. You get medicines before the shot to prevent this. Redness at the shot site is common and mild.

Infections

Daratumumab and lenalidomide can lower your defenses against germs. Colds and chest infections are the most common. Stay up to date on vaccines, wash your hands, and call for a fever.

Tiredness

Some people feel more tired on treatment. Gentle daily activity, like walking, and good sleep help. Tell your care team if it gets in the way of daily life.

Low blood counts

Lenalidomide can lower white blood cells and platelets. You will have regular blood counts, and the dose can be adjusted.

Blood clots

Lenalidomide raises the risk of blood clots. Most people take aspirin or another blood thinner to prevent them. Call right away for leg swelling or sudden shortness of breath.

Rash, diarrhea, or muscle cramps

These can happen with lenalidomide. Tell your care team. Simple changes and medicines can often help.

Living with MGUS or smoldering myeloma

Most people with MGUS live a normal life and never need treatment. Many people with smoldering myeloma also stay stable for years. Keeping your follow-up visits is the most important thing you can do.

Know your numbers. Ask for a copy of your M-protein and light chain results, and keep a simple log. If you move or change doctors, bring your past results so the trend can be followed.

Learn the warning signs. New bone or back pain, unusual tiredness, frequent infections, foamy urine, leg swelling, or numbness in your feet should be checked. Do not wait for your next scheduled visit if something new comes up.

Protect your bones and kidneys. Stay active, get enough calcium and vitamin D, and avoid smoking. Ask before taking pain pills like ibuprofen or naproxen often. Drink enough fluids unless told otherwise.

Keep up with vaccines and general health care, including cancer screening that fits your age. MGUS does not mean you should skip other care.

Close family members have a slightly higher chance of MGUS, but routine screening of relatives is not usually advised. Groups like the International Myeloma Foundation and the Multiple Myeloma Research Foundation offer free information and support.