Solitary plasmacytomas of bone and extramedullary plasmacytomas. A clinicopathologic and immunohistochemical study.

Twenty-two patients with solitary plasmacytoma of bone (SPB) and 13 with extramedullary plasmacytomas (EMP) were studied. The average follow-up period for SPB was 90 months and 86 months for EMP. Thirty-six percent of patients with SPB developed multiple myeloma (MM) in an average of 39 months, and 23% of patients with EMP developed MM in an average of 23 months. No significant differences in survival, incidence of MM, or interval to the development of MM were found between the two groups. The 11 cases of EMP with evaluable tissue for immunohistochemical study were either monotypic kappa or lambda, as were 9 of 10 SPB. Presence of monoclonality did not predict the development of MM. The histologic parameters of nuclear immaturity and presence of prominent nucleoli seem to be the best indicators of which patients will develop MM. Solitary plasmacytoma of bone and EMP appear to be more closely related than has been previously recognized.