Plasmacytoma

Plasmacytoma is a localized neoplastic proliferation of monoclonal plasma cells forming a discrete mass. It most often arises as solitary plasmacytoma of bone (SPB) or as solitary extramedullary plasmacytoma (EMP) in soft tissues, frequently in the head and neck region. By definition, plasmacytoma is distinct from multiple myeloma, which shows systemic bone lesions, anemia, hypercalcemia, renal impairment, or widespread marrow involvement.

SPB occurs within a single bone, commonly the vertebrae or skull, causing bone pain or fracture. EMP grows as a soft-tissue mass, often in the nasopharynx, sinuses, or oropharynx, and may cause nasal obstruction, epistaxis, dysphagia, or airway symptoms.

Diagnosis requires tissue biopsy showing clonal plasma cells with light-chain restriction; imaging defines the solitary lesion; bone marrow biopsy must show no clonal plasma cells and no other systemic myeloma features; laboratory studies include serum and urine protein electrophoresis/immunofixation to detect monoclonal protein and serum free light chains. PET-CT or MRI may help exclude additional lesions.

Radiation therapy is the primary treatment for both SPB and EMP, with typical doses around 40-50 Gy in 20-25 fractions. Surgery may be used to remove accessible masses or to palliate symptoms, particularly in EMP of the head and neck. Systemic chemotherapy is not routinely used unless there is progression to multiple myeloma or additional disease. Patients with EMP often respond well to radiotherapy, with high local control rates.

Solitary plasmacytomas have a risk of progression to multiple myeloma over time, particularly SPB; long-term follow-up is essential. Factors associated with higher risk of progression include persistent M protein after treatment, large tumor size, and incomplete response. Regular monitoring includes physical exams, labs to detect M protein, renal function, calcium, anemia, and repeat imaging as indicated.