Monoclonal gammopathy of undetermined significance (MGUS) is a condition in which a person has moderately elevated levels of an abnormal immunoglobulin protein called M protein in the blood.

As in multiple myeloma, MGUS begins in a type of white blood cells called plasma cells, which produce M protein. Moderately elevated levels of this protein in the blood rarely result in symptoms, but some people with MGUS may experience peripheral neuropathy — pain or burning in the hands and feet.

MGUS has been linked to exposure to certain chemicals. In particular, US Air Force veterans who participated in the spraying missions of the herbicide Agent Orange during the Vietnam War have a more than twofold increased risk of developing the condition. Researchers from MSK provided the first direct evidence linking Vietnam veterans exposed to Agent Orange with MGUS.

MGUS can be precancerous. Even after many years of remaining stable, it may progress to multiple myeloma or another blood disease, either amyloidosis or Waldenström’s macroglobulinemia. However, this occurs in a very small percentage of people. Most people with MGUS remain well for many years without ever developing active disease.

Because of the slight risk your condition could progress, if you have MGUS you should have your protein levels monitored through regular blood tests. Monitoring can typically be done by your primary care doctor under the guidance of doctors at Memorial Sloan Kettering.

As long as the levels of M protein do not rise, MGUS requires no treatment.