MGUS and multiple myeloma both cause elevated levels of monoclonal antibodies in your blood. MGUS usually has no symptoms but can be a precursor to multiple myeloma.

MGUS is a noncancerous condition that causes the plasma cells in your blood to produce abnormal antibodies called monoclonal proteins (M proteins).

Although MGUS is a precursor to multiple myeloma, a blood cancer in the bone marrow also due to M proteins, MGUS rarely progresses to this serious disease.

The plasma cells in your bone marrow are white blood cells that create antibodies. Antibodies are proteins that protect your body from bacteria and viruses.

If your plasma cells create copies of abnormal proteins, called monoclonal proteins or M proteins, it may lead to a rare condition called monoclonal gammopathy of unknown significance (MGUS).

“Monoclonal” refers to the abnormal copies of antibodies. “Gammopathy” is the production of these antibodies, known as gamma globulins. “Unknown significance” means what causes this hasn’t been determined.

People with MGUS usually have no symptoms and don’t need treatment. It’s often discovered following a routine blood test.

MGUS affects males more than females, and Black people more than white or Asian people. About 3% of people over 50 years old and 5% of people over 70 years old have MGUS, according to a 2022 review of research.

Multiple myeloma is a rare type of blood cancer that, like MGUS, causes an abnormal plasma cell to quickly reproduce and take over the production of healthy plasma cells.

The abnormal cells are called myeloma cells. Instead of producing antibodies, they create M proteins. This prevents your body from fighting infections and can affect areas of your body beyond your bone marrow.

Unlike in MGUS, the myeloma cells may lead to bone and organ damage. The typical symptoms of multiple myeloma have the acronym CRAB:

  • C: high levels of calcium in the blood
  • R: renal (kidney) dysfunction
  • A: anemia
  • B: bone disease

About 1.8% of all new cancer cases are multiple myeloma. It’s most often diagnosed in people who are 65 years old and older. As with MGUS, multiple myeloma affects males more than females. It’s over twice as common in Black people than in white people.

There’s no cure for multiple myeloma. Your outlook depends on factors such as its stage at diagnosis, your age and overall health, and how well the cancer responds to treatment. The overall 5-year survival rate is 59.8%.

Although people with MGUS have a greater risk of multiple myeloma, MGUS progresses to this cancer in only about 1% of cases.

Your risk is higher if you have specific markers in your blood. A 2019 study involving 685 people with MGUS suggests that the level of these markers may change within 5 years, so people who had a low risk of developing multiple myeloma may eventually have a high risk.

Based on these findings, researchers recommend annual blood testing for everyone with MGUS, regardless of their risk level.

MGUS vs. smoldering multiple myeloma vs. active multiple myeloma

MGUS and smoldering multiple myeloma (SMM) may be earlier stages of multiple myeloma.

  • People with MGUS have low levels of M protein in their blood and abnormal plasma cells in their bone marrow.
  • People with SMM have higher levels of M protein and plasma cells, with no damage to their bones, red blood cells, or kidneys. During the first 5 years, there is a 10% chance SMM progresses to active multiple myeloma.
  • People with active multiple myeloma have the highest level of this protein and plasma cells as well as damage to their bones, red blood cells, or kidneys.
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If you have MGUS and experience any of the following early symptoms of multiple myeloma, talk with a doctor:

  • back, hip, or rib pain
  • numbness or muscle weakness, especially in your legs
  • shortness of breath
  • fatigue
  • nausea

A doctor may order some of the following tests to detect an increased level of M protein in your blood, which could indicate multiple myeloma:

  • complete blood count
  • blood chemistry tests to measure albumin, calcium, creatinine, and electrolyte levels
  • serum protein electrophoresis to measure the antibodies in your blood and detect the M protein
  • protein electrophoresis urinalysis detects M protein in a urine sample
  • serum-free light chain analysis can measure the level of light chains, a type of immunoglobulin present in light chain myeloma
  • bone marrow, fine needle aspiration, or core needle biopsy to detect whether there are too many plasma cells in your bone marrow
  • bone scan, CT scan, or MRI to reveal areas of your body that may have cancer and whether the cancer is spreading
  • X-rays, which may show damage to your bones due to myeloma cells

The M protein level in the blood of people with MGUS is typically lower than 3.0 grams per deciliter, and the presence of bone marrow monoclonal plasma cells is less than 10%.

According to the American Cancer Society, a multiple myeloma diagnosis requires either a plasma cell tumor or more than 10% monoclonal plasma cells in your bone marrow and at least one CRAB symptom.

No available treatments can prevent MGUS from progressing to multiple myeloma. For most cases of multiple myeloma, there are no risk factors to avoid.

It’s important to have annual blood tests so that if your MGUS does progress to multiple myeloma, doctors can detect it in its earliest stages, increasing the chances of successful treatment.

The following are the answers to some frequently asked questions about the differences between MGUS and multiple myeloma.

Does MGUS always turn into multiple myeloma?

No. It’s very rare for MGUS to progress to multiple myeloma. This happens in only around 1% of cases.

What are the three types of MGUS?

The type of M protein immunoglobulins in your blood determines the type of MGUS you have:

  • IgM MGUS: Up to 15% of people with MGUS have IgM immunoglobulins in their blood.
  • Non-IgM MGUS: Most people have one of the other immunoglobulins: IgG, IgA, IgD, or IgE.
  • Light-chain MGUS: M proteins typically have a light chain and a heavy chain. In light-chain MGUS, they only have a light chain.

Non-IgM MGUS and light-chain MGUS have a higher risk of progressing to multiple myeloma.

How long does it take for MGUS to turn into multiple myeloma?

The time it may take for MGUS to progress into multiple myeloma varies by person. The risk of this happening may also change.

A 2019 study suggests that within 5 years, people who receive a diagnosis of low risk MGUS may become more at risk due to increased levels of M proteins or free light chains in their blood.

Although MGUS rarely progresses to multiple myeloma, this risk may increase over time.

It’s important to undergo regular blood testing. This can lead to earlier detection and a more positive outcome if your MGUS develops into multiple myeloma or another disease.