Prognostic factors in solitary plasmacytoma of the bone: a multicenter Rare Cancer Network study

Data from 206 patients with bone SP without evidence of multiple myeloma (MM) were collected. Histopathological diagnosis was obtained for all patients. The majority (n = 169) of the patients received RT alone; 32 chemotherapy and RT, and 5 surgery. Median follow-up was 54 months (7–245).Five-year overall survival, disease-free survival (DFS), and local control was 70%, 46%, and 88%; respectively. Median time to MM development was 21 months (2–135) with a 5-year probability of 51%. In multivariate analyses, favorable factors were younger age and tumor size < 5 cm for survival; younger age for DFS; anatomic localization (vertebra vs. other) for local control. Older age was the only predictor for MM. There was no dose-response relationship for doses 30 Gy or higher, even for larger tumors.Younger patients, especially those with vertebral localization have the best outcome when treated with moderate-dose RT. Progression to MM remains the main problem. Further investigation should focus on adjuvant chemotherapy and/or novel therapeutic agents.Solitary plasmacytoma (SP) is a rare plasma-cell neoplasm [1]. There are two separate entities, dependent on the location of the lesion originating in either bone or extramedullary soft tissue [2]. It is defined as a proliferation of monoclonal plasma cells without evidence of significant bone-marrow plasma-cell infiltration [1]. Bone SP is characterized by a unique lesion involving any part of the squeleton, most commonly in the spine.Recommendations for the choice of treatment modalities in this radiosensitive disease [3] are based mainly on data from retrospective studies often considering relatively small numbers of patients, with a limited ability to make any robust conclusions [4,5], and only one prospective study including 53 patients [6].Definitive radiation therapy (RT) is the treatment of choice for solitary plasmacytoma giving adequate local control. However, with respect to long-term outcome, it is known that bone plasm