Incidence and Prognostic Value of Bone and Extramedullary Plasmacytomas in Patients with Newly Diagnosed Multiple Myeloma: Data from a Prospective Population-Based Study

BACKGROUND. The etiology of plasmacytomas in multiple myeloma (MM) remains unclear, whereas the pathogenetic mechanisms of extramedullary lesions are of particular importance because of extremely poor prognosis. The incidence of bone and extramedullary plasmacytomas complicating the course of MM as well as the efficacy of therapy for this disease are still underresearched. AIM. To assess the incidence of bone and extramedullary plasmacytomas in patients with newly diagnosed MM (ndMM) and analyze the overall survival (OS) rates depending on whether soft-tissue components were detected. MATERIALS & METHODS. This multi-center prospective study enrolled 3184 ndMM patients (1339 men and 1845 women) from 40 regions of Russia, aged 24–90 years and treated during the period from January 2015 to October 2018. The electronic patient records included demographic, clinical, laboratory, and instrumental documentation data accessible on MM diagnosis date. Bortezomib-based regimens were administered in the first-line therapy to 94 % of patients. RESULTS. Bone and extramedullary plasmacytomas were diagnosed in 763 (24 %) out of 3184 ndMM patients. At disease onset, the median hemoglobin concentration was significantly higher in patients with bone (105 g/L) and extramedullary (102 g/L) plasmacytomas than in patients without them (95 g/L; p < 0.05). The median percentage of plasma cells in the bone marrow was significantly lower in cases of bone plasmacytoma accounting for 25 % vs. 30 % in cases of extramedullary components, and it was 31 % in patients without plasmacytomas at MM onset (p < 0.05). Most commonly, plasmacytomas were detected in the thoracic spine (24.3 %; n = 132) and ribs (13.6 %; n = 74). The median OS of patients without plasmacytomas was 46 months (95% confidence interval [95% CI] 43–49 months) vs. 38 months (95% CI 42–46 months) in patients with them (p = 0.1245). The median OS was 17 months (95% CI 10–35 months) in patients with extramedullary plasmacytomas and 13 months (95% CI 1–69 months) if soft-tissue components were detected in the bones of the lower extremities. CONCLUSION. The course of ndMM is complicated by bone plasmacytomas in 23 % of cases and extramedullary plasmacytomas in 1 % of cases. The antitumor response rate as well as the OS rates are similar in patients with and without bone plasmacytomas. Extramedullary lesions in MM are associated with extremely low rate of OS with the median not exceeding 17 months.