Establishment of an innovative staging system for extramedullary plasmacytoma

BACKGROUND: Extramedullary plasmacytoma (EMP) is a rare malignant disease that lacks a unique clinical staging system to predict the survival of EMP patients and to design individualized treatment. Instead, clinicians have chosen to use the multiple myeloma (MM) staging system. METHODS: Forty-eight EMP patients treated between 1996 and 2014 were included in this study. The new clinical stages were established according to independent survival factors using Cox regression model. RESULTS: Lymph node metastasis and a larger primary tumor (≥5 cm) were the only two independent poor prognostic factors for overall survival (OS) and disease-free survival (P < 0.05). Stage I was defined as the disease without those two poor prognostic factors. Stage II was defined as the presence of either factor, and Stage III was defined as the presence of both factors. OS was significantly different in each stage of the new staging system (P < 0.001), with a median follow-up time for Stage I, Stage II and Stage III of 68, 23 and 14 months. The new staging system had enhanced prognostic value compared to the MM staging system (the area under ROC 0.763 versus 0.520, P = 0.044). Although no difference was observed between treatments in Stage I, the combination treatment was associated with a significantly beneficial OS in the late stages (5-year OS: 15.3 % versus 79.5 %; P = 0.032). CONCLUSIONS: The new staging system exhibited a promising prognostic value for survival and could aid clinicians in choosing the most suitable treatment for EMP patients.