Clinical Course of High-Risk Multiple Myeloma Patients in Korea: A Multicenter Retrospective Study

Introduction: Increased understanding of the pathophysiology of multiple myeloma (MM) and the introduction of new drugs has led to considerable survival improvements in recent years. The International Myeloma Working Group consensus recently updated the definition for high-risk MM based on cytogenetic abnormalities. Moreover, the recent introduction of new therapeutic agents and the revision of insurance reimbursement policies have changed the clinical characteristics of MM patients in Korea. Yet, current epidemiology and the clinical characteristics of MM patients in Korea have not been fully investigated. Therefore, we aimed to understand the characteristics and management of Korean MM patients in a real-world setting by analyzing patients with high-risk cytogenetic abnormalities in the Korean Myeloma Registry.

Methods: This is a retrospective observational study using the Korean Myeloma Registry, the web-based multicenter patient registry system established by the Korean Multiple Myeloma Working Party. Patients who are newly diagnosed with MM from 2010 to 2017 with at least one high-risk cytogenetic abnormality [t(4;14), t(14;16), or del(17p)] were included. Primarily, patients were classified by cytogenetic abnormality into three groups: Group 1, t(4;14) or t(14;16); Group 2, del(17p); and Group 3, t(4;14)/del(17p) or t(14;16)/del(17p). These patients were also stratified by the revised International Scoring System (R-ISS) and transplantation history for detailed analysis. We also used the number of cytogenetic abnormalities in an explanatory analysis; in this case, we included gain(1q). Progression-free survival (PFS) and overall survival (OS) were estimated, and the Hazard Ratio with the log-rank test was used for statistical comparison.

Results: 391 out of 2170 MM patients from seven hospitals were identified as high-risk patients (men, 49.6%; median age, 63 years old). Median PFS for all patients was 18.9 months (95% CI 17.27-20.33), and the median OS was 44.6 months (95% CI 36.5-60.1).

PFS (P<0.001) and OS (P=0.012) between the cytogenetic abnormality groups were significantly different after stratification by transplant history. Patients with t(4;14)/del(17p) or t(14;16)/del(17p) amongst transplant recipients showed the worst outcome, with median PFS 15.5 (95% CI 8.7-20.5) months and median OS 35.6 (95% CI 14.9-N/A) months. Without stratification, there were no significant between-group differences in PFS and OS.

OS was also significantly different between cytogenetic abnormality groups stratified by the revised International Staging System (R-ISS) (P=0.003). The lowest median OS durations were 16.9 months (95% CI 6.5-33.6) for del(17p) with R-ISS III, and 21.7 months (95% CI 9.3-N/A) for t(4;14)/del(17p) or t(14;16)/del(17p) with R-ISS III. Patients with higher R-ISS staging in the presence of del(17p) showed worse survival outcomes.

Finally, PFS and OS were significantly inversely correlated with the number of cytogenetic abnormalities (P<0.001).

Conclusion: In real-world data from the Korean Myeloma Registry, we were able to observe the association of poor prognosis of MM patients with the number of cytogenetic abnormalities (PFS and OS) and R-ISS (OS). Moreover, we were also able to find the association of cytogenetic abnormality del(17p) and poor prognosis in MM patients. Lastly, we believe that this study provides the characteristics and management of MM patients needed to understand the real-world clinical course of high-risk MM patients in South Korea.

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