P967: TUMOR BURDEN AS A CRITICAL PROGNOSTIC FACTOR OF PRIMARY EXTRAMEDULLARY DISEASE

Abstract

Background: Multiple myeloma (MM) is the second most common hematological malignancy characterized by malignant plasma cell (PC) infiltration of the bone marrow (BM). In the case of extramedullary MM (EMD), plasma cells survive and proliferate outside of the bone marrow microenvironment. Primary EMD is found in newly diagnosed MM (NDMM) patients. Aims: The aim of this study was to describe clinical features and treatment outcomes of primary EMD patients and to define possible risk factors. Methods: In total, 724 primary EMD patients were diagnosed in the Czech Republic between 2004 and 2021 by using modern imaging methods. As a reference group, 2440 MM patients without any evidence of EMD were used. All patients enrolled into the analysis were treated by novel agents. Patients’ data were analyzed from the Registry of Monoclonal Gammopathies of the Czech Myeloma Group (RMG). Results: Primary EMD patients had less frequently advanced ISS (ISS 3) (OR 0.51 [95% CI: 0.42–0.63], p<0.001), high paraprotein levels (>20g/l) (OR 0.64 [95% CI: 0.54–0.76], p<0.001) and high PC infiltration of bone marrow (>10%) (OR 0.35 [95% CI: 0.30–0.42], p<0.001) when compared to reference MM patients. Median PFS in newly diagnosed primary EMD patients was comparable to reference MM patients (23.2 months [95% CI: 21.2–26.2] vs. 23.3 months [95% CI: 22.5–24.8], p=0.800). Median OS was comparable to reference patients (52.6 months [95% CI: 46.3–62.0] vs. 55.0 months [95% CI: 51.6–58.9], p=0.504). By multivariate analysis, adjusted for ISS, we found high levels of BM PCs (>10%) together with 3 and more EMD lesions as an independent risk factor for inferior survival in primary EMD patients (PFS: HR 1.92 [95 % CI: 1.28–2.87]; OS: HR 2.06 [95 % CI: 1.35–3.14], both p=0.001). Summary/Conclusion: We found primary EMD patients distinct from reference MM patients. Survival intervals of both groups of patients were comparable. We found that the intra- and extramedullary tumor burden is an independent key factor influencing primary EMD prognosis. This work was supported by grant AZV NU21-03-00076.