Plasmacytoma and multiple myeloma are similar cancers of the plasma cells in the blood or bone marrow. However, these types of cancer have key differences. In people with multiple myeloma, cancerous plasma cells develop diffusely throughout the bone marrow and cause problems, such as decreased blood cell counts as well as kidney and other organ dysfunction. In plasmacytoma, the abnormal plasma cells form together in a mass in one area of the body, most commonly in a bone. The incidence (rate of new cases) of plasmacytoma is low, with less than 5 percent of those with plasma cell disorders having a plasmacytoma.

Plasma Cell Disorders

There are multiple types of plasma cell disorders. Plasma cells are made in the bone marrow from B cells, white blood cells that make up part of the immune system. Plasma cells make immunoglobulins (antibodies) that help the body fight off an infection. When these plasma cells become abnormal, a plasma cell disorder develops. These disorders may include amyloidosis, monoclonal gammopathy of unknown significance, plasmacytoma, and multiple myeloma.

What Is Multiple Myeloma?

When plasma cells grow uncontrollably in the bone marrow, multiple myeloma develops. In multiple myeloma, the plasma cells form an abnormal protein called an M spike, monoclonal protein, or M protein. These abnormal proteins build up in the bone marrow and other organs and prevent them from functioning properly.

As the proteins grow in the bone marrow, other blood cells made in the bone marrow are unable to grow normally. As a result, low levels of platelets (thrombocytopenia) and red blood cells (anemia) may develop.

The abnormal proteins can also build up in other organs, and organ failure such as kidney failure can develop.

Read more about multiple myeloma.

What Is Plasmacytoma?

A plasmacytoma is similar to multiple myeloma because it is caused by abnormal plasma cells. However, instead of being located throughout the bone marrow, these abnormal plasma cells collect into one mass, most often located in a bone. Although uncommon, a plasmacytoma can form outside of a bone, which is called an extramedullary plasmacytoma. People with plasmacytoma may sometimes later develop multiple myeloma.

Types of Plasmacytoma

In general, there are two types of plasmacytoma: solitary bone plasmacytoma and extramedullary plasmacytoma.

Solitary Bone Plasmacytoma

When cancerous plasma cells form a solid lesion in one area of a bone, this is called a solitary bone plasmacytoma. These tumors usually develop in the spinal column, but they may also develop in the pelvis, femur (thigh), and sternum (breast bone). Additionally, there are no symptoms or other findings to support a diagnosis of multiple myeloma, such as elevated calcium levels, renal disease, or anemia.

Extramedullary Plasmacytoma

In people with extramedullary plasmacytomas, the solid mass of cancer cells does not form in the bone marrow or a bone but rather in the soft tissue of an organ in the body. These plasmacytomas occur most commonly in the soft tissues of the head and neck area, such as the sinuses or upper respiratory tract. They can also form in other organs such as the bladder or gastrointestinal tract. People with extramedullary plasmacytoma do not have other findings supportive of a multiple myeloma diagnosis.

Symptoms of Plasmacytoma

Symptoms caused by solitary bone plasmacytomas depend on where the cancerous lesion (tumor) is growing. There will likely be bone pain in the location of the tumor because the bone is usually destroyed as cancer grows. If the tumor is growing in the spine and is putting pressure on the spinal cord, symptoms such as weakness or loss of bowel or bladder function can develop.

An extramedullary plasmacytoma may cause symptoms depending on the organ that is affected by the tumor. A person with this condition may present with pain due to organ compression or enlargement.

Diagnosing Plasmacytoma

Diagnosing plasmacytoma is a multistep process that involves blood tests, imaging studies, and a biopsy. These tests are often the same as those used to diagnose multiple myeloma and may include:

• Complete blood count, which determines the levels of white blood cells, red blood cells, and platelets in the blood
• Complete metabolic panel, which includes tests for levels of calcium and other electrolytes, kidney function, and liver function
• Blood immunoglobulin and blood protein electrophoresis
• Urine tests including Bence-Jones protein tests and urine protein electrophoresis
• Free light-chain test
• Imaging tests such as X-rays, CT scan, MRI, or positron emission tomography (PET) to look for any solid lesions in the body

Sometimes, a bone marrow biopsy or a biopsy of the tumor may be necessary to confirm a diagnosis and rule out multiple myeloma.

Treating Plasmacytoma

For plasmacytomas of bone, treatment typically consists of radiation therapy to kill the cancerous bone lesion. To treat extramedullary plasmacytomas, treatment may vary depending on the location of the plasmacytoma. Surgery, radiation, chemotherapy, or a combination of these treatments may be used for an extramedullary tumor.

As plasmacytomas are rare, few clinical trials have shown optimal treatments. Further research is needed to help treat plasmacytoma and reduce the risk of plasmacytoma later developing into multiple myeloma.

Risk of Multiple Myeloma

Having a diagnosis of either solitary bone plasmacytoma or extramedullary plasmacytoma comes with an increased risk of developing multiple myeloma. Studies have reported that having a bone plasmacytoma is a risk factor. One study published in 2017 showed an average of 21 months (approximately two years) before myeloma development. Up to 84 percent of people in the study developed multiple myeloma within 10 years of their bone plasmacytoma diagnosis.

The risk is lower for people with extramedullary plasmacytoma. The study showed that 71 percent of those with extramedullary plasmacytoma had not developed multiple myeloma within 10 years.

Talk With Others Who Understand

MyMyelomaTeam is the social network for people with multiple myeloma and their loved ones. On MyMyelomaTeam, more than 12,000 members come together to ask questions, give advice, and share their stories with others who understand life with multiple myeloma.

Are you living with a bone plasmacytoma or extramedullary plasmacytoma? Share your experience in the comments below, or start a conversation by posting on MyMyelomaTeam.