Types of Myeloma

In its broadest terms, multiple myeloma may be categorized as either smoldering or active.

However, there are many types and subtypes, which are based on the type of immunoglobulin (antibodies) produced by the myeloma cells. This information is important, as it may drive myeloma treatment choices.

Myeloma cells secrete abnormal immunoglobulins that are unable to properly fight infection. Immunoglobulins have different functions. These molecules are made up of two heavy chains and two light chains.

Heavy chains: IgG, IgA, IgD, IgE and IgM

Light chains: kappa (κ) or lambda (λ)

The various subtypes are:

• IgG kappa
• IgA kappa
• IgD kappa
• IgE kappa
• IgM kappa
• IgG lambda
• IgA lambda
• IgD lambda
• IgE lambda
• IgM lambda

In IgG kappa, the most common type of myeloma, myeloma cells produce an immunoglobulin made from two IgG heavy chains bound to two kappa light chains.

Smoldering Myeloma

Smoldering multiple myeloma is the term health care providers use to refer to early-stage disease that isn’t yet causing any myeloma symptoms. Smoldering myeloma is a precancerous condition affecting certain proteins in the blood. It may also lead to an increase in plasma cells in bone marrow.

Specific tests may help doctors predict a patient's risk of smoldering myeloma progressing to active disease. The average patient has about 10% per year risk of progressing from smoldering myeloma to active disease, requiring treatment, but for some the risk may be higher.

Health care providers typically adopt a watch-and-wait approach to smoldering multiple myeloma, carefully watching for any sign that the disease is progressing before starting treatment.

Active Myeloma

Active myeloma is blood cancer that is on the move. People with active myeloma meet CRAB criteria, with damage to bones, red blood cells and/or kidneys, or have myeloma-defining events based on predictive markers in the blood or identified by imaging.

Does Smoldering Myeloma Always Become Active?

Not everyone with smoldering myeloma develops symptoms and requires treatment. Nearly half of patients have not progressed in the first five years, and one-third remain progression-free at 10 years, according to long-term studies noted in a 2018 review in Blood Advances.

Light Chain Myeloma

About 15% of myelomas are considered light chain myelomas, according to Cancer Research UK, which are also known as Bence-Jones myeloma.

In this form of the blood cancer, myeloma cells secrete light chain proteins only. These light chains build up in tissues as an abnormal protein known as amyloid. When amyloid builds up in organs such as the heart or kidneys, it may do damage and interfere with proper function.

Non-Secretory Myeloma

Just 1% to 5% of people with myeloma have non-secretory myeloma, according to the International Myeloma Foundation. In this form of the disease, myeloma cells produce little or no abnormal immunoglobulin. That differs from other forms of the disease, in which myeloma cells release antibodies into blood and urine. Non-secretory myeloma may be challenging to diagnose, as telltale secretions don’t show up in the blood.

Less Common Myeloma Types

Some subtypes of myeloma are even less common.

Solitary Plasmacytoma of Bone

With a plasmacytoma, abnormal plasma cells build up in one place to form a tumor. If this occurs in just one area of the body, it is a solitary plasmacytoma.

Representing 3% to 5% of all plasma cell disorders, according to the National Cancer Institute (NCI), solitary plasmacytoma of bone is a form of multiple myeloma in which the tumor is made up of abnormal plasma cells in the skeleton. These tumors typically develop in the spine, but they may also occur in the pelvis, ribs, arms, face, skull, thigh and breastbone. The condition affects more males than females. About two-thirds of people with solitary plasmacytoma of bone will develop multiple myeloma within 10 years, according to the NCI.

This form of myeloma tends to develop in people between the ages of 55 and 65.

Extramedullary Plasmacytoma

Plasmacytoma outside the bone is called a solitary extramedullary plasmacytoma.

These tumors are typically found in the head and neck, but they may also develop in the gastrointestinal tract, lymph nodes, bladder, lung or other organs. Solitary extramedullary plasmacytoma progression to myeloma occurs in about 15% of patients, according to a 2023 StatPearls review.