Comparison of clinical features of multiple myeloma with paraosseous and extraosseous plasmacytoma in the era of novel drugs: a systemic review and meta-analysis.

BACKGROUND: Extramedullary myeloma has a more aggressive clinical course and inferior prognosis. Two types of extramedullary myeloma, paraosseous (PO) and extraosseous (EO), differ significantly in pathogenesis, clinical features, and outcomes, but there have been limited studies comparing them based on large patient cohorts. METHODS: Relevant studies published before June 2021 were searched in MEDLINE, Embase, and Cochrane databases. Two reviewers independently assessed the quality of included studies, and discrepancies were evaluated by a third reviewer. Extracted data were analyzed by Stata 12. RESULTS: Nine hundred ninety-seven MM patients with PO and 288 with EO plasmacytoma were analyzed. Patients with EO plasmacytoma tended to have larger tumor burden according to the International Staging System though it did not reach statistical significance (P = 0.1). Newly diagnosed MM (NDMM) patients with EO plasmacytoma had significantly inferior outcome than those with PO plasmacytoma (OS: OR = 2.32, 95% CI 1.80-2.98, P < 0.001, I2 = 40.9%; PFS: OR = 1.66, 95% CI 1.39-1.99, P < 0.001, I2 = 0.0%). No significant difference in OS was found in relapsed MM patients. Auto-HSCT seemed to attenuate the disadvantage in response rate of EO plasmacytoma. CONCLUSIONS: NDMM patients with EO plasmacytoma had significantly inferior prognosis than those with PO plasmacytoma, while relapsed MM patients did not show such difference. More strategies are needed to improve its clinical outcome.