Smoldering multiple myeloma is a rare disorder that can lead to a cancer called multiple myeloma.

Typically, smoldering multiple myeloma (SMM) has no symptoms, which can make it difficult to detect.

There is only one type of SMM. The disorder has different stages depending on how far it has progressed. We explore stages, treatment, and progression of this disorder.

Blood in a test tube which may reveal smoldering multiple myelomaShare on Pinterest
SMM is often spotted during unrelated blood or urine tests.

SMM is caused by unhealthy plasma cells. Plasma cells are part of the immune system that fights off disease. Plasma cells form in the bone marrow, which is the spongy tissue within the bones.

When a person has SMM, their body makes too many plasma cells. These cells are abnormal and create unhealthy antibodies called M proteins.

Usually, antibodies recognize bacteria and viruses that cause disease and stop them from harming the body. However, M proteins do not work like normal antibodies, as they do not fight disease. Instead, M proteins build up in the bone marrow and can cause problems if they reach a certain level. In most cases of SMM, however, there are not enough M proteins in the body to cause damage.

SMM does not usually have any symptoms, so it may go undiagnosed; however, it may be spotted during blood or urine tests that are being carried out for a separate medical issue.

Rarely, SMM can develop into a type of cancer called multiple myeloma. SMM makes up around 5 percent of all cases of multiple myeloma and is not considered an active form of the disease.

Although there is only one type of SMM, it has three different stages:

  • Stage 1: A certain level of unhealthy cells exist, but they are not increasing in number.
  • Stage 2: Myeloma that is progressing slowly without causing damage to the body.
  • Stage 3: Myeloma that is progressing moderately without causing noticeable damage.

If a person is diagnosed with SMM, they will be closely monitored to check which stage the disorder has reached.

MGUS (EM-gus) stands for monoclonal gammopathy of undetermined significance. MGUS is a stage before SMM and the disorder also creates too many unhealthy plasma cells and M proteins (though less than in SMM). Although MGUS results in higher levels of these cells in the bone marrow, they do not usually cause any symptoms or any damage to a person's blood, bones, or kidneys.

Around 1 percent of people with MGUS will develop multiple myeloma, lymphoma, or amyloidosis per year.

Lymphoma refers to a group of blood cancers. Amyloidosis is a group of rare conditions that stop organs and tissues in the body from working properly.

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Regular medical checkups are recommended to ensure that SMM is not progressing.

SMM and MGUS do not usually cause damage to the body. For this reason, a person who has one of these disorders will not usually require treatment.

However, a person with SMM will need to have regular medical checkups to ensure the disorder is not progressing or becoming cancerous.

The schedule of appointments will usually be as follows:

  • a follow-up appointment 2 to 3 months after SMM is diagnosed
  • if the results of tests are normal, appointments every 4 to 6 months for 1 year
  • if the results of tests are normal after 1 year, appointments every 6 to 12 months

Treatment will be given if SMM progresses to multiple myeloma. Treatment will usually include chemotherapy drugs and pain medication but may also include a stem cell transplant.

Research is ongoing into the relationship between SMM and multiple myeloma. Part of this research involves clinical trials, which are often carried out to test new medications and treatments.

A person with SMM may wish to take part in a clinical trial. They can discuss this with a doctor to find out more about possible risks and benefits, as well as whether there are trials available in their area.

Around 10 percent of people with SMM will develop multiple myeloma in the 5 years after diagnosis.

After 5 years, the risk of developing multiple myeloma drops to 3 percent per year.

Abnormal plasma cells can create tumors in tissue or bone. If one tumor forms, the disease is known as a plasmacytoma. More than one tumor is called multiple myeloma.

Tumors can cause weakened bones, damage the kidneys, and lead to high levels of calcium in the blood. Symptoms include bone pain, anemia, numbness, and a higher risk of infection or illness.

MGUS and SMM do not usually have any symptoms, but they can sometimes lead to health problems.

Levels of M protein in the body can cause tingling or numbness in the hands or feet. The medical term for this feeling is peripheral neuropathy.

MGUS and SMM can weaken the bones, which means that people who have these disorders are at greater risk of developing osteoporosis. Osteoporosis is a condition that causes bones to become less dense and more fragile. Weak bones are more likely to break or fracture.

People with MGUS and SMM are more than twice as likely to get an infection than the rest of the population. This is because their immune system is weaker, which means their body produces fewer healthy antibodies that can fight disease.

To prevent getting an infection, anyone with SMM or MGUS should consider avoiding friends and relatives who have a contagious illness, such as the flu. Washing hands and having a flu vaccination can also help protect against disease.

SMM is not a cancer. The risk of the disorder becoming multiple myeloma is relatively low, but it should be closely monitored.

As SMM does not have any symptoms, many people do not realize that they have it. If a person is diagnosed with SMM, they will be offered regular medical appointments to monitor the stage and progression of the disorder.