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Myeloma is a type of cancer that affects plasma cells. Plasma cells are a part of the immune system; they are responsible for making antibodies (immunoglobulins), which are proteins that help fight off infections.

Blood cells, including plasma cells, are made in the innermost part of the bone called the bone marrow. If plasma cells have a mutation that changes how often cells duplicate, cells can begin to multiply uncontrollably, forming a tumor. When these cancer cells spread to other sites — or metastasize — the condition is called multiple myeloma.

Origin of Multiple Myeloma

A plasma cell tumor found in one localized region of the body is called a solitary plasmacytoma. If plasma cells cause a tumor in the bone marrow, the tumor is called a solitary bone plasmacytoma (SBP). SBP is often detected in the ribs, femur, spine, and pelvic bone.

If the plasma cell tumors are located in the soft tissue or an organ, then the disease is called extramedullary plasmacytoma (EMP). EMPs can occur in any organ of the body, but they are most often found in the upper respiratory tract.

“Plasmacytoma” refers to a single tumor, while “multiple myelomas” means that there are multiple tumor sites.

Common Sites for Multiple Myeloma

Myelomas can be found in many bones, including the spine and ribs. The most common sites of myelomas include the:

• Pelvis
• Spine
• Long bones, like the femur
• Skull
• Ribs

Because the cancerous cells slowly destroy the bone, people with multiple myeloma typically complain of having bone pain, often in their lower back. This symptom can be easily overlooked, since back pain can be caused by many factors. People over the age of 50 who have back pain lasting longer than a month should see their doctor. However, metastatic myelomas are not limited to bones.

How Does Myeloma Spread Through the Body?

Cancerous cells leave the bone marrow through the bloodstream, just as normal immune cells leave the bone marrow to help fight off infections. The cancerous cells can then travel throughout the body to form more tumors.

The Role of Extramedullary Disease in Metastasis

When myeloma cells spread, they can form a tumor in the soft tissues or organs of the body. Multiple extramedullary tumors occur when the cancer has metastasized; this condition is called extramedullary disease.

Extramedullary disease is considered metastasis once there are multiple soft tissue tumors. However, some people can have a single EMP in the soft tissue that does not metastasize into multiple myeloma.

Extramedullary myeloma cells can be located:

• In soft tissues next to bone
• In soft tissues or organs not connected to bone
• In an organ as diffused (widely spread) plasma cells without a centralized lesion

Extramedullary lesions can be found in people who have just been diagnosed with myeloma and in patients who have had a myeloma relapse (a return of symptoms after a period of improvement). They are most frequently found in the soft tissue next to the bones with myeloma. Less often, lesions are found in the skin, liver, central nervous system, or kidneys.

Incidence and Metastasis in Myeloma

Overall, myelomas are a fairly uncommon type of cancer. About 7.1 new myeloma cases per 100,000 people are diagnosed each year in the United States. Multiple myeloma is the most common type of plasma cell tumor, with a lifetime risk of 0.76 percent.

SBP has a rate of 0.45 per 100,000 people in the United States. Extramedullary disease is rare, affecting about 7 percent to 15 percent of people newly diagnosed with myeloma. People who have relapsed from myeloma have a slightly increased risk of extramedullary disease, ranging from 6 percent to 20 percent.

Health care providers find it difficult to detect myeloma early, before the disease has metastasized, because many myeloma symptoms are also found in many other conditions. These symptoms include back pain, nausea, loss of appetite, fatigue, constipation, and excessive thirst. Some people do not experience any symptoms and discover they have the disease during a routine blood exam. Because it can go unnoticed, myeloma is typically detected after metastasis.

SBP is more likely to metastasize to multiple myeloma than EMP. SBP has a 50 percent progression rate, whereas 15 percent of EMP cases will progress to multiple myeloma. A population-based study from the Netherlands found that 70 percent of people with SBP progressed to multiple myeloma.

Although there currently is no cure for myeloma, survival rates continue to improve for people living with myeloma. Cancer treatments also continue to advance. Learn more about treatments for multiple myeloma.

Talk With Others Who Understand

MyMyelomaTeam is the social network for people with myeloma and their loved ones. On MyMyelomaTeam, members come together to ask questions, give advice, and share their stories with others who understand life with myeloma.

Are you living with multiple myeloma? Share your experience in the comments below, or start a conversation by posting on your Activities page.