Last revised by Henry Knipe on 11 Jun 2024

Plasmacytomas are discrete, solitary tumors of neoplastic monoclonal plasma cells in either bone or soft tissue (extramedullary). It is a rare tumor that is associated with latent systemic disease in the majority of affected patients. In contradistinction to multiple myeloma, there is minimal or no systemic bone marrow involvement.

Solitary plasmacytomas can be divided into two groups according to location:

Plasmacytoma diagnosis requires a solitary lesion on imaging with tissue biopsy demonstrating monoclonal plasma cells (typically expressing CD138 and/or CD38) on histology and immunohistochemistry 7.

  • overall, solitary plasmacytoma represent 3-6% of all plasma cell neoplasia (i.e. including multiple myeloma, plasma cell leukemia) 4

  • usually occur in patients between 40 and 80 years of age

  • the median age is 55 years, that is 10 years younger than patients with multiple myeloma

The most common symptom of solitary bone plasmacytoma is pain at the site of the skeletal lesion due to bone destruction by the infiltrating plasma cell tumor.

A plasmacytoma can arise in any part of the body. A solitary bone plasmacytoma arises from the plasma cells located in the bone marrow, whereas extramedullary plasmacytoma is thought to arise from plasma cells located in mucosal surfaces. Both represent a different group of neoplasms in terms of location, tumor progression, and overall survival rate. Both do, however, share many of the biologic features of other plasma cell disorders.

Serum/urine electrophoresis will show elevated M protein in ~50% (range 33-64%) of patients at diagnosis with the level (<1 g/dL) lower than multiple myeloma (>3 g/DL) 8.

Plasmacytoma (as with multiple myeloma) are typically seen as well-defined, “punched-out” lytic lesions with associated extraosseous soft-tissue masses, similar in appearance to most metastatic lesions. In advanced plasmacytoma, there is often marked erosion, expansion, and destruction of the bone cortex, sometimes with thick ridging around the periphery, creating a “soap bubble” appearance. 

CT may demonstrate subtle lytic lesions or small soft-tissue masses, particularly of the sternum, that are not visible at radiography. 

Use of short-inversion-time inversion recovery and contrast-enhanced fat suppression techniques may improve the sensitivity of MR imaging.

Treatment may consist of radiotherapy alone, surgery alone, or a combination of the two depending on location and resectability of the plasmacytoma 6. Solitary bony plasmacytomas are highly radiosensitive with local control rates of greater than 80% 6.

Three patterns of failure indicating poorer prognosis include development of multiple myeloma, local recurrence, and development of new lesions 6. The progression rate to multiple myeloma is higher in solitary bone plasmacytoma (65-85% at 10 years) than extramedullary plasmacytoma 6.

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