Monoclonal gammopathy of undetermined significance (MGUS) is not cancer. There’s a small risk it can become cancer. Out of every 100 people with MGUS, each year, 1 or 2 of them will get cancer from MGUS.

MGUS (pronounced like EM-gus) is when your blood makes an abnormal (not normal) protein called m-protein. It’s a blood disorder that often starts in older people after age 50.

You may be at higher risk for MGUS if you:

• Are Black.
• Were assigned male at birth.
• Were exposed to pesticides.

We do not know what causes MGUS. There may be a link to autoimmune diseases, genetics, or environmental factors.

Like multiple myeloma, MGUS starts in a type of white blood cell called plasma cells. These cells make m-protein. This abnormal protein can build up in your blood and urine.

Blood and urine tests can show if you have MGUS, or show signs it’s getting worse. These tests look for how much m-protein is in your blood, and what kind of m-protein you have.

MGUS signs and symptoms

People with MGUS do not have symptoms or signs of multiple myeloma. Some people feel peripheral neuropathy (peh-RIH-feh-rul noor-AH-puh-thee). This is numbness, tingling, or pain in your hands and feet.

Living with MGUS

MGUS can be precancerous, which means it can become cancer. It can be stable for many years, and then turn into another condition. This change happens with very few people. Most people with MGUS never get a more serious condition.

MGUS can turn into multiple myeloma. It also can turn into another blood disease, either:

• Amyloidosis
• Waldenström’s macroglobulinemia (VAHL-den-strum MA-kroh-GLAH-byoo-lih-NEE-mee-uh). Waldenström’s is a type of non-Hodgkin lymphoma that grows slowly. It’s a rare white blood cell cancer that often starts in bone marrow. It’s also called lymphoplasmacytic lymphoma.

Treating MGUS

If you have MGUS, your protein levels should be monitored through regular blood tests. You will not need treatment for MGUS as long as the level of m-protein does not rise.

Your MSK care team can guide your local healthcare provider as they monitor MGUS.

They will watch to see if MGUS becomes another blood disease. If that happens, your MSK doctors can treat plasma cell disorders or multiple myeloma.