Solitary plasmacytoma of bone vs. extramedullary plasmacytoma and their relationship to multiple myeloma.

Solitary plasmacytoma of bone (SPB) and extramedullary plasmacytoma (EMPC) are unusual solitary tumors of plasma cell origin. The clinical differences between these tumors and multiple myeloma are the subject of continued study. This review examines the radiotherapy experience at M. D. Anderson Hospital. Between 1948 and 1977, 12 patients with SPB and 12 patients with EMPC were treated with radiotherapy. Radiotherapeutic doses were most often (22/24) greater than 4,000 rads, at 200 rads per day. In order to qualify as solitary plasmacytoma a disease-free interval of 3 years was required. In the group of SPB, 5 patients of 9 were alive with no evidence of disease (NED) at 3 years, 4 of 5 at 5 years, and none of 4 at 10 years. In the EMPC group, 8 patients of 11 were NED at 3 and 5 years, and 6 of 9 at 10 years. Six patients with SPB developed multiple myeloma compared with only two with EMPC. The results confirm the better prognosis of EMPC and support the theory that SPB and EMPC are two different entities.