Solitary Plasmacytoma

What plasma cells do

Plasma cells develop from B lymphocytes and produce antibodies (immunoglobulins). In plasma cell disorders, one abnormal plasma cell multiplies to form a clone that often produces a single type of antibody, called a monoclonal protein (M-protein) or paraprotein. These disorders range from MGUS, a common, usually harmless condition, to solitary plasmacytoma and multiple myeloma.

Solitary plasmacytoma vs multiple myeloma

Types

Solitary bone plasmacytoma

• the more common type, about two-thirds or more of cases
• most often in the spine (vertebrae), then the ribs, pelvis, skull and long bones
• typically in adults in their 50s and 60s, more often men
• higher risk of progressing to multiple myeloma: a majority of patients within about 10 years in older series, although modern imaging that excludes hidden disease has improved staging

Extramedullary plasmacytoma

• occurs in soft tissue, most commonly in the upper airway: nose, sinuses, nasopharynx, tonsils, larynx
• can also occur in the gut, lungs, lymph nodes or skin
• lower risk of progression to myeloma than bone plasmacytoma

Symptoms

Bone plasmacytoma

• persistent localized bone pain, often in the back
• a fracture from minimal trauma (pathologic fracture)
• with spinal lesions: nerve root pain, numbness or weakness, and in severe cases spinal cord compression

Extramedullary plasmacytoma

• one-sided nasal blockage, discharge or nosebleeds
• a lump in the throat, hoarseness or trouble swallowing
• swelling of the face or neck

Diagnosis

The International Myeloma Working Group defines solitary plasmacytoma as:

1. a biopsy-proven single lesion of clonal plasma cells
2. normal bone marrow with no clonal plasma cells (or under 10% in "solitary plasmacytoma with minimal marrow involvement")
3. normal whole-body imaging apart from the primary lesion
4. no myeloma-related organ damage (no high calcium, kidney failure, anemia or other bone lesions)

Tests include:

• biopsy of the lesion
• bone marrow aspirate and biopsy, including flow cytometry
• blood and urine tests: serum protein electrophoresis, immunofixation, serum free light chains, blood count, calcium and kidney function
• whole-body PET-CT or MRI to exclude other lesions

Treatment

• radiation therapy: the standard treatment. A dose of about 40 to 50 Gy delivered over several weeks controls the tumor locally in most patients
• surgery: to stabilize a fractured or unstable bone, decompress the spinal cord, or remove some extramedullary tumors; usually followed by radiation
• systemic therapy (chemotherapy or myeloma drugs) is not routinely given but may be considered for high-risk features, large tumors, or incomplete response

Follow-up and outlook

Regular follow-up, typically every few months at first, includes blood and urine protein tests and periodic imaging. Persistence or rise of the M-protein after treatment suggests a higher risk of progression.

• extramedullary plasmacytoma: local control rates are high, and many patients are cured
• solitary bone plasmacytoma: local control is also high, but progression to multiple myeloma is common over time, which is then treated as myeloma

Frequently asked questions

What is a solitary plasmacytoma?

It is a single tumor made of abnormal plasma cells, either in a bone (most often the spine) or in soft tissue such as the nose or throat. Unlike multiple myeloma, there is only one lesion and the bone marrow is otherwise normal or nearly normal.

Is solitary plasmacytoma cancer?

Yes. It is a type of plasma cell cancer. It is treated with radiation and often controlled or cured, but bone plasmacytoma frequently progresses to multiple myeloma over years, so lifelong follow-up is needed.

How is solitary plasmacytoma treated?

The main treatment is radiation therapy to the tumor. Surgery may be needed to stabilize a broken bone or relieve pressure on the spinal cord. Systemic myeloma treatment is considered only in selected high-risk cases.

Does solitary plasmacytoma turn into multiple myeloma?

It can. Solitary bone plasmacytoma has a substantial risk of progressing to multiple myeloma over 10 years. Extramedullary plasmacytoma has a lower risk. Regular blood tests and imaging help detect progression early.