Racial Difference in Part D Enrollment and Survival Among Older Patients with Multiple Myeloma

Introduction Multiple myeloma (MM) is the second most common hematologic malignancy in the United States. African Americans (AAs) are disproportionately affected by MM.Previous studies found that among patients with MM, when having equal access to treatment, AAs had better survival than Whites. Oral agents, e.g., immunomodulatory drugs, play an active role in the treatment of both newly diagnosed and relapsed or refractory MM. For Medicare patients, these oral agents are covered by Part D only. However, little is known about the potential role of Part D enrollment in racial difference among older patients with MM.

Methods Using the Surveillance, Epidemiology, and End Results-Medicare linked database, we conducted a population-based cohort study to assess the role of part D enrollment and race in MM survival. The study included AA and White patients with first primary MM (International Classification of Diseases for Oncology-3^rd edition, 9732) who 1) were diagnosed from 2007-2017, 2) ages ≥ 66 years at diagnosis, and 3) had continuous Parts A & B enrolment and were not a member of HMO from 12 months before diagnosis to end of follow-up (death or 12/31/2019, whichever came first). Patients were categorized as ever or never enrolled in Part D. We applied a published algorithm to define smoldering and symptomatic MM patients. Our outcome of interest is overall survival. Cochran-Armitage trend test was used to test trend of Part D enrollment by year of diagnosis. Kaplan-Meier curves were generated, and log-rank tests were used for comparisons across groups. Hazard ratios (HR) and 95% confidence intervals (CI) were estimated from a multivariable Cox proportional hazards model, adjusting for demographics, comorbidities, and socioeconomic factors. All statistical tests were two-sided with a type I error of 0.05 and were performed with SAS Version 9.4.

Results The final cohort included 17,097 patients with a median follow-up of 2.64 (interquartile range [IQR] 0.81-4.78) years for 3,315 AAs and 2.58 (IQR 0.70-4.72) years for 13,782 Whites. The median age of AAs was 75 ([IQR 70-80) and of Whites 76 (IQR 71-82) years. Compared with Whites, AAs were more likely to be female, younger, unmarried, diagnosed in more recent years, had a high Elixhauser score, be frail, have state buy-in, and reside in census tracts with 20-100% population below poverty (all p_s<.01). However, AAs were less likely to have a diagnosis of symptomatic MM (69.0% vs 71.0%, p=0.02).

During the follow-up, 85.7% AAs and 78.1% Whites were ever enrolled in Part D (p<.01). Among both races, Part D enrollment increased over years (p_trend<.01). AAs had higher Part D enrollment percentage than Whites in both smoldering MM (AAs 88.8%, Whites 84.7%, p<.01) and symptomatic MM groups (AA 84.3%, Whites 75.4%, p<.01).

The median survival was 3.05 (95% CI 2.85-3.24) years for AAs and 2.86 (95% CI 2.75-2.97) years for Whites (p<.01). Smoldering MM patients who ever had Part D enrollment had highest median survival; among these patients, AA had higher median survival (5.76, 95% CI 5.39-6.62 years) than their White counterparts (4.94, 95% CI 4.71-5.15 years; Figure 1).

In the multivariable models, Part D enrollees (vs non-enrollees) had better overall survival (p<.01), and the interaction term between race and Part D enrollment was statistically significant for all patients (p=0.04) and smoldering patients (p<.01). As shown in Figure 2, among patients who were ever enrolled in Part D, compared to Whites AAs had lower risk of death (HR=0.88, 95% CI 0.83-0.93, p <.01), especially among smoldering MM patients (HR=0.78, 95% CI 0.70-0.87, p<.01). However, among patients never enrolled Part D, no difference on survival (HR=0.99, 95% CI 0.89-1.11, p=0.92) was observed.

Conclusions Among patients who ever enrolled in Part D, AAs, especially with smoldering MM, had better survival than Whites, yet there was no racial difference in survival among patients who never had Part D coverage. A higher percentage of Medicare Part D enrollment in AAs than that in Whites may help explain the racial difference in survival observed in MM patients. Future research is needed to evaluate patterns of MM care by both race and Part D enrollment.

Acknowledgement This study was supported by grant 1U01CA265735-01. The contents are solely the responsibility of the authors and does not necessarily represent the official views of funding agency.

Wang:Celgene: Research Funding. Neparidze:Janssen: Research Funding; GSK: Research Funding. Ma:Bristol Myers Squibb: Consultancy.