Impact of Extended Treatment Interval on the Prognosis of Multiple Myeloma Patients: A Retrospective Study

Introduction: Recently, treatment with proteasome inhibitors and immunomodulators has improved the prognosis of multiple myeloma (MM). However, in a complex real-world situation, the patient’s ability to undergo regular and timely treatment as prescribed in clinical trials has not been studied, as well as the impact of extended treatment intervals due to different reasons. This study aimed to evaluate the treatment interval and clinical characteristics of 122 patients with primary myeloma in our hospital and explore the prognostic effects of different treatment intervals. Methods: In total, 122 patients with MM were analyzed retrospectively in our hospital from January 2007 to June 2018. The clinical and laboratory data (such as age, International Staging System [ISS] stage, chromosome, etc.) and subsequent treatment intervals were analyzed. The Cox proportional hazard regression model was used for univariate and multivariate analyses of overall survival (OS) and progression-free survival. The Kaplan-Meier method was used in survival analysis, and the log-rank test was used to test survival difference. p < 0.05 was considered to indicate statistical significance. Results: We found that prolonging the interval treatments (>28 days) shortened the OS in the younger and high-risk subgroups. On the contrary, the OS of the older and low-risk subgroups was not shortened. OS was also shortened in patients who were suitable for transplantation but did not receive a transplant. Univariate and multivariate analyses showed that extension of treatment interval was a risk factor for OS shortening. In addition, prolonged treatment interval was due to iatrogenic and family reasons. Conclusion: Extended treatment interval is unfavorable in young and high-risk MM patients and those suitable for transplantation but who did not receive a transplant. However, it has a faint impact on the elderly and low-risk subgroups.