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A few plasma cell disorders involve unusual plasma cell growth but don’t meet the criteria for active multiple myeloma. These include:

• Monoclonal gammopathy of undetermined significance (MGUS)

• Solitary plasmacytoma
• Smoldering multiple myeloma (SMM)
• Light chain amyloidosis

To learn more about the criteria used to diagnose the different plasma cell disorders, see Tests for Multiple Myeloma.

Monoclonal gammopathy of undetermined significance (MGUS)

In monoclonal gammopathy of undetermined significance (MGUS), abnormal plasma cells make many copies of the same antibody (called a monoclonal protein). However, these plasma cells don’t form an actual tumor or mass, and they don’t cause the other health problems that can be seen in multiple myeloma.

MGUS doesn’t damage bones or cause high calcium levels, kidney problems, or low blood counts. It’s most often found when a routine blood test finds a high level of protein in the blood and further testing shows the protein is a monoclonal antibody.

In MGUS, the number of plasma cells may be increased, but they still make up less than 10% of the cells in the bone marrow.

MGUS is not considered cancer, but some people with MGUS will eventually develop a cancer such as multiple myeloma or lymphoma. They might also develop amyloidosis, a condition linked with blood cancers (see below). Each year, about 1% of people with MGUS develop one of these diseases. The risk is greater in people whose monoclonal protein levels are particularly high.

People with MGUS don’t need treatment, but they are watched closely to see if they get a disease that does need to be treated, such as multiple myeloma.

Solitary plasmacytoma

A plasmacytoma is a type of plasma cell tumor. Rather than many tumors in different locations as in multiple myeloma, there is only one tumor, hence the name solitary plasmacytoma.

A solitary plasmacytoma often develops in a bone. When a plasmacytoma starts in other body tissues (such as the lungs or other organs), it is called a solitary extramedullary (or extraosseous) plasmacytoma.

Solitary plasmacytomas can usually be treated with radiation therapy and/or surgery. As long as no other plasmacytomas are found later on, the person’s outlook is usually excellent. However, people with a solitary plasmacytoma might develop multiple myeloma later, so they need to be watched closely for signs of this disease.

Smoldering multiple myeloma ?(SMM)

Smoldering multiple myeloma (SMM), also known as asymptomatic myeloma, is an early form of myeloma that is not causing any symptoms. People with smoldering myeloma have some signs of multiple myeloma, such as any of the following:

• A higher-than-normal amount of plasma cells in the bone marrow
• A high level of monoclonal immunoglobulin (monoclonal protein) in the blood
• A high level of light chains (also called Bence Jones protein) in the urine

However, they have normal blood counts, normal calcium levels, normal kidney function, no bone or organ damage, and no signs of amyloidosis (see below).

Most people with smoldering multiple myeloma don’t need treatment right away, because the disease can take anywhere from many months to years to become active (symptomatic) myeloma.

Some people may have very slow disease that never becomes active myeloma, but for others the risk is higher, so earlier treatment might be helpful.

To learn more, see Treatment Options for Multiple Myeloma and Other Plasma Cell Disorders.

Light chain amyloidosis

Light chain amyloidosis (also known as AL amyloidosis or primary amyloidosis) is also a disorder of abnormal plasma cell growth, but with lower amounts of abnormal plasma cells in the bone marrow compared to multiple myeloma.

Monoclonal proteins (antibodies) are made up of joined protein chains – 2 short light chains and 2 longer, heavy chains. In light chain amyloidosis, abnormal plasma cells make too many light chains. The light chains build up in tissues as an abnormal protein known as amyloid.

The buildup of amyloid in certain organs can enlarge them and affect the way they work. For example:

• W?hen amyloid builds up in the heart, it can cause an irregular heartbeat and can make the heart larger and weaker. A weak heart can lead to a condition called congestive heart failure, with symptoms like shortness of breath and swelling in the legs.
• Amyloid in the kidneys can affect how well they work. This may not cause symptoms early on, but the poor kidney function may be seen on blood tests. If it gets bad enough, it can lead to kidney failure.

To learn more, see Signs and Symptoms of Multiple Myeloma.

Light chain amyloidosis is only one of the diseases where amyloid builds up and causes problems. Amyloidosis can also be caused by a genetic (hereditary) disease called familial amyloidosis. Long-standing (chronic) infection and/or inflammation can also cause amyloidosis. This is known as secondary or AA amyloidosis.

Waldenstrom macroglobulinemia (WM)

The cancer cells in people with WM are similar to those in multiple myeloma and non-Hodgkin lymphoma (NHL). Multiple myeloma is considered a cancer of plasma cells, and non-Hodgkin lymphoma is a cancer of lymphocytes. WM cells have features of both plasma cells and lymphocytes.

Lymphocytes are one of the main types of white blood cells in the immune system. They include T cells and B cells, and they are in many areas of your body, including your lymph nodes, bone marrow, intestines, and bloodstream. When B cells respond to an infection, they mature and change into plasma cells.

Even though WM is sometimes grouped with other plasma cell disorders, it is considered a type of NHL.

To learn more, see Waldenstrom Macroglobulinemia.