The treatment of solitary plasmacytoma consists of local radiation which is effective in achieving long-term control in 90% of cases. About two thirds of solitary plasmacytomas of the bone eventually progress to multiple myeloma. The median time to progression is 2 to 3 years but may be as long as 10-15 years. The factors associated with greater risk of progression include advanced age, lesions larger than 5 cm, and persistence of M protein after local irradiation. Even after progression to multiple myeloma, the disease pursues an indolent course and responds well to chemotherapy.