The workup of a patient thought to have multiple myeloma may reveal a solitary plasmacytoma. A solitary plasmacytoma is a single cancer site that may involve the bone (osseous) or other tissues (extraosseous or extramedullary). Solitary plasmacytomas represent approximately 5% of all patients with myeloma.
Diagnosis of a solitary plasmacytoma requires a very thorough evaluation to ensure that there is not the presence of myeloma elsewhere in the body. This is because many patients who are presumed to have solitary plasmacytoma, are ultimately found to have evidence of myeloma elsewhere. Following complete evaluation, patients with solitary plasmacytoma can be treated with radiation therapy alone, as studies have indicated that the addition of chemotherapy to radiation does not improve overall survival in patients with solitary plasmacytoma.
Radiation therapy for solitary plasmacytoma typically delivers between 40 and 50 Gy. Treatment with radiation is associated with up to 50% of patients with solitary bone plasmacytoma being alive without evidence of recurrence 10 years from treatment, suggesting that many patients with solitary plasmacytoma can be cured. Prognosis may be even better for patients with solitary extramedullary plasmacytoma. Both osseous and extraosseous or extramedullary plasmacytomas are treated with radiation therapy.
 Rajkumar SV, Dispenzieri A, Kyle RA. Monoclonal gammopathy of undetermined significance, Waldenström macroglobulinemia, AL amyloidosis, and related plasma cell disorders: diagnosis and treatment. Mayo Clinic Proceedings. 2006;81:693-703.