MYC translocation is a valuable marker for the development and relapse of extramedullary disease in multiple myeloma

Abstract Objective To study the cytogenetic characteristics of extramedullary disease (EMD) in patients with multiple myeloma (MM) and their impact on prognosis. Methods Patients with newly diagnosed MM (NDMM) at Peking Union Medical College Hospital (Beijing, China) between June 2007 and December 2019 were recruited for this study. Demographic information, clinical data, fluorescence in situ hybridization (FISH) results of marrow and tissue samples, and survival outcome data were collected. Results A total of 439 patients with NDMM were divided into those without EMD (non‐EMD, n = 339), those with EMD with primary paraosseous plasmacytoma (pEMD‐B, n = 48), those with primary EMD with soft‐tissue involvement (pEMD‐S, n = 33), and those with secondary EMD (sEMD, n = 19). The incidence of EMD was 18.5% (81/439) at diagnosis and 22.8% (100/439) throughout the disease course. Comparison of FISH results showed a higher proportion of RB1 deletion ( n = 20; 60.0% vs. 20.0%, p = .013) and MYC translocation ( n = 12; 44.4% vs. 12.5%, p = .041) in the extramedullary tissues than in the paired bone marrow samples. At diagnosis, the percentage of MYC translocations in the sEMD group was notably higher than that in the non‐EMD group (55.6% vs. 15.5%, p = .012). The median overall survival (OS) of patients with pEMD‐S (32 months) and sEMD (17 months) was significantly shorter (both p = .001) than that of non‐EMD patients (60 months). Conclusion Soft‐tissue EMD can be considered a high‐risk condition, even in the era of novel agents. MYC translocation can serve as a valuable marker that correlates with extramedullary spread and relapse in patients with MM and should be considered for inclusion in routine FISH panels in clinical practice.