Monoclonal Gammopathy of Undetermined Significance (MGUS)

June 4, 2026

This page was reviewed under our medical and editorial policy by Leslie L. Popplewell, M.D., Hematologist and Chief of Hematology, City of Hope^® Cancer Center Atlanta.

Monoclonal gammopathy of undetermined significance (MGUS) is a type of blood disorder that begins in the body’s plasma cells. It is considered precancerous, meaning MGUS is not cancer, but it may develop into blood cancer over time. About 4% of Americans are diagnosed with MGUS each year.

What is MGUS?

MGUS is a precancerous blood disorder that causes changes in how the body’s plasma cells work. In people with MGUS, abnormal plasma cells produce a type of monoclonal immunoglobulin, sometimes referred to as an M-protein. There are several different types of MGUS, named for which kind of immunoglobulin is involved.

MGUS is not cancer, and it does not usually require treatment. However, it may progress to become a type of blood cancer called multiple myeloma or, in rarer cases, to other types of blood disorder or cancer.

Is MGUS Hereditary?

Hereditary conditions only develop if a child inherits a genetic mutation from one or both parents. MGUS is not hereditary, because it does not appear to be linked to inherited gene mutations. However, studies have shown that people who have a direct family member with MGUS are more likely to develop the condition too. In addition to a family history of MGUS, other risk factors for the disorder include:

• Being an adult over the age of 70
• Being of Black or African-American descent
• Being male
• Having an autoimmune condition, such as rheumatoid arthritis, though more research is needed to confirm a connection between these conditions and MGUS

MGUS Symptoms

Most people with MGUS experience no symptoms or signs of the disorder. However, if MGUS progresses to active multiple myeloma, the patient may experience some of the symptoms of multiple myeloma, such as fatigue, weakened or painful bones or an increase in infections.

MGUS Diagnosis

MGUS is usually diagnosed using blood tests and urine samples that measure the levels of M-proteins in the patient’s body. Many of these tests are also used to diagnose multiple myeloma and are ordered or performed by a hematologist, who is a doctor who specializes in blood disorders. There are several different types of MGUS, named for the type of M-protein (or immunoglobulin) being produced, as detailed below.

IgG and IgA MGUS: These are the most common types of MGUS. They produce immunoglobulin G or immunoglobulin A, respectively. These types of MGUS may become myeloma, as well as other conditions such as solitary plasmacytoma or amyloidosis.

IgM MGUS: This is less common and produces immunoglobulin M. It may develop into Waldenstrom macroglobulinemia, amyloidosis or myeloma.

Light chain MGUS: This type of MGUS produces light chain immunoglobulins (components of immunoglobulins). It may develop into myeloma, solitary plasmacytoma or amyloidosis.

Risk of MGUS Becoming Cancer

The overall risk that MGUS will develop into multiple myeloma is 1%. This level of risk does not appear to increase over time, no matter when MGUS is diagnosed. MGUS may also develop into some other types of blood disorder, but the risk that it will progress to these conditions is lower. They include:

• Amyloidosis
• Lymphoma
• Solitary plasmacytoma
• Waldenstrom macroglobulinemia

Because MGUS does not tend to cause any symptoms, it usually requires no treatment. However, patients with MGUS should undergo regular screening and testing to check whether the condition has progressed.

MGUS Versus Multiple Myeloma

Around 1% of people with MGUS who are aged 50 or older develop multiple myeloma. This figure increases to about 3% among patients over the age of 70. The risk is also higher in patients with serum M-protein over 1.5g/dL, non-IgG MGUS (IgA, IgM, IgD) and for those who have an abnormal serum light chain ratio. If none of these risk factors exist, the risk of progression over 20 years is about 5%. While MGUS and multiple myeloma are similar in some ways, there are also some crucial differences between the two conditions. For instance:

• MGUS is precancerous, meaning it is not cancer (multiple myeloma is a type of blood cancer)
• MGUS does not usually cause symptoms, whereas multiple myeloma may cause symptoms such as fatigue, bone pain, immune system issues and frequent infections
• MGUS does not usually require treatment, while multiple myeloma patients must undergo treatment to stop or reverse the progression of cancer