Health Insurance-Related Disparities in Lymphoma Survival Are Partly Mediated by Baseline Clinical Factors

Pulte et al. [1] described significant insurance-related disparities among younger patients with non-Hodgkin lymphoma (NHL), with hazard ratios for overall survival of 1.92 and 2.51 in the uninsured or Medicaid populations, respectively. Their findings complement recently identified disparities in diffuse large B-cell lymphoma (DLBCL) survival by socioeconomic status, particularly pronounced among patients less than 65 years old [2]. However, the Surveillance, Epidemiology and End Results data set used by Pulte et al. lacks important confounders of survival in NHL: performance/comorbidity status, human immunodeficiency virus (HIV) status, the International Prognostic Index (IPI) [3], and chemotherapy use. We further explored those insurance-related disparities using the National Cancer Data Base (NCDB), a joint project of the American Cancer Society and the Commission on Cancer of the American College of Surgeons, which captures more than 70% of incident cancer cases in the United States. Advantageously, the NCDB contains data on the Charlson-Deyo comorbidity index [4], HIV status, chemotherapy administration and the IPI in a subset (11%) of all reported DLBCL cases. Among 5,797 patients aged 18–64 years diagnosed with DLBCL between 2004 and 2011, those confounders had a significantly different prevalence among groups with various types of health insurance (Table 1). In particular, nearly a quarter of those younger Medicaid patients were HIV-positive, and more than 40% had high-intermediate or high IPI, compared with only 27% of patients with private insurance. Additionally, Medicaid and Medicare beneficiaries had higher rates of comorbidities. This is explained by eligibility criteria for those state-sponsored programs, which are tied to medical disability in the younger age groups. Table 1. Confounders of survival in diffuse large B-cell lymphoma among patients aged 18–64 years with different types of health coverage In multivariable Cox models adjusting for age, sex, race, comorbidity index, and stratified by the IPI, HIV status, and stage (which violated the proportional hazard assumption), the adjusted hazard ratios for overall survival were: 1.26 for the uninsured (95% confidence interval [CI], 1.05–1.52), 1.52 for Medicaid (95% CI, 1.31–1.76), and 1.47 for Medicare (95% CI, 1.26–1.71). These estimates, although still significant, were notably lower than those calculated by Pulte et al., indicating that the insurance-associated disparities are partly mediated by prevalence of known prognostic factors in DLBCL or by patients’ pre-existing medical conditions that determine eligibility for specific health insurance. The relative risk of nonreceipt of chemotherapy (adjusted for the same confounders) in a robust Poisson model was 1.58 (95 CI, 1.15–2.18) for the uninsured, 1.60 (95% CI, 1.23–2.09) for Medicaid, and 1.65 (95% CI, 1.24–2.19) for Medicare, demonstrating direct disparity in the delivery of standard curative treatment. Cancer registries constitute a popular data source for the study of disparities, but they offer limited insight into their cause. Our results highlight that to quantify and interpret such disparities, confounders related to patients’ baseline status or disease biology have to be separated from socioeconomic factors affecting health care quality that could respond to policy or system interventions [5, 6]. Another layer of complexity may arise from differences in histologic or molecular characteristics. Those remain largely unexplored, although they may also confound racial or socioeconomic disparities, as recently shown in some hematologic malignancies [7, 8].