Secondary Malignancies in Multiple Myeloma in Korean Patients: A Nationwide Population-Based Study.

Purpose:This study investigated the incidence of secondary malignancy in multiple myeloma (MM) patients compared with that in the general population using a population-based database covering all residents in Korea. Materials and Methods:Based on the national health insurance system in Korea, all people primarily diagnosed with MM between January 1, 2010 to December 31, 2018 were identified. A total of 9,985 MM patients aged ≥20 years in Korea were included. Results:Among them, 237 (2.4%) developed secondary malignancies by 2018. The standardized incidence rates (SIRs) of all secondary malignancies in MM patients were 0.87 (95% confidence interval [CI]=0.76-0.98), with a higher incidence of hematologic malignancies than in the general population with an SIR of 3.80 (95% CI=2.61-5.00). The incidence rates of both lymphoid malignancy (SIR=3.56; 95% CI=2.31-4.82) and myeloid malignancy (SIR=3.78; 95% CI=1.16-6.39) were higher in MM patients than in the general population. In contrast, a lower incidence of solid cancer was observed in MM patients than in the general population (SIR=0.76, 95% CI=0.65-0.86). There was no significant difference in survival in MM patients without secondary malignancies, with hematologic malignancy, and with solid cancer (p-value=0.413). Conclusion:MM patients had a greater risk of secondary malignancies, especially hematologic malignancies, than the general population. Future studies with a focus on analyzing patients' history, treatment details, and genetic information in various stages of MM patients are needed to better understand the mechanism behind this increased risk.