DISCUSSION
Overall, non-Hispanic whites had the highest 10-year survival, with non-Hispanic blacks, Hispanics, and Other having a worse survival. Considering histologic types, anaplastic astrocytoma and glioblastoma had the lowest survival and diffuse astrocytoma (protoplasma, fibrillary) and mixed glioma had the highest survival. This is consistent with findings from previous studies.8,28,29,30,31,32 This study differs from other studies of pediatric brain and CNS tumor survival because it assesses the racial disparities in brain and CNS tumor survival using recent national specialized census tract data that provide information on both SES and cancer treatment received by patients.
The largest group of minority patients were Hispanics, which is not surprising because Hispanics are currently the largest racial minority and one of the fastest growing racial minority groups in the US.33 Similar to what was found in other studies6,11,12 there was a male predominance in diagnosed cases and the majority of cases were diagnosed before age ten. Pilocytic astrocytoma was found to be the most common tumor type in children, with non-Hispanic whites having the highest proportion of cases. This concurs with findings from other studies.6,12 It was also previously shown that non-Hispanic blacks had the highest burden of medulloblastoma,34 however, similar to the findings of Cooney, et al. and Barnholtz-Sloan et al.,7,11 our study showed Hispanics had the highest burden of both medulloblastoma and ependymoma. “Other” race/ethnicities had the highest proportion of anaplastic astrocytoma and glioblastoma histology types. Studies that examined these histologies separately found that non-Hispanic whites had an increased proportion of glioblastoma tumors8 while non-Hispanic blacks had an increased proportion of anaplastic astrocytoma.11
Even though our study showed a strong association between race and SES, similar to Austin and Kehm’s findings,6,22 SES was not significantly associated with adverse cancer outcomes in the univariate and multivariate models for both 5-year and 10-year risk of death. Accounting for SES in the multivariate model reduced the risk of death across all racial groups. This supports findings from previous studies on the relationship between SES and solid tumor outcomes demonstrating that low SES is not associated with poor survival outcomes.6,22 Results from our study suggest that factors other than SES mediate the racial survival disparities observed in brain and CNS tumors.
Examining the multivariate analysis, we found that the 10-year hazard of death was significantly increased for all three minority racial groups as compared to non-Hispanic whites, with Hispanics having the highest risk of death. Survival reaches a plateau for most tumors quite late with the exception of high-grade gliomas and medulloblastoma.35,36,37 It is thus not surprising that in our study, the racial/ethnic survival disparities were more pronounced in the 10-year models. Late mortality could also occur in 5-year survivors, attributable to multiple causes including late treatment effects, tumor recurrence or progression which could be influenced by quality of initial therapy.38,39,40 It will be informative to look at the cause-specific mortality for cases.
The relatively poor 5-year survival seen among Hispanics could be due to multiple factors. Based on the study results, Hispanics have the highest proportion of patients undergoing partial lobectomy. This procedure was associated with an increased 5-year risk of death based on the study results. Similar to finding from other studies6,41, our results showed that Hispanics have a slighter higher burden of cases reporting with advanced cancer compared to the other racial groups. It may stem from the fact that the affected individuals may be uninsured/underinsured which is influenced by several factors including parents’ immigration status and healthy families who choose to forgo insurance.42,43
In our study, we found significant differences in treatment modality by race/ethnicity, which may partially explain the increased risk of death seen in minority racial groups. Similar treatment differences were noted in a study which addressed the disparities in brain tumor treatment.13 Considering that treatment received is known to impact survival,19 patients who receive inadequate treatment or poor quality treatment have less chances of survival. Minority populations as compared to non-Hispanic whites often receive treatment from low volume hospitals which are less equipped to handle such cases rather than high volume hospitals or specialized cancer centers where they can receive adequate and quality care from a multidisciplinary clinical team for both initial therapy and follow up care for survivors.10,13,38 Furthermore, there is evidence to suggest that racial discrimination on the part of healthcare providers, minority patients being less likely to be enrolled in clinical trials, and patients declining treatment options due to mistrust of the health system contribute to disparities in treatment.13,20,44,45,46,47,48 There could also be racial differences in the response to chemotherapeutics due to potential differences in pharmacogenomics and tumor molecular markers across the racial/ethnic groups.49,50 However, there doesn’t appear to be a documentation of raced-based biological differences in these factors and the extent to which they impact treatment outcomes.37 Future studies should specifically explore host and tumor genetic factors and its influence on treatment response across racial groups.
Challenges with patient provider communication especially when it involves patients with limited English proficiency (LEP), the majority of which are from minority racial groups51 could negatively impact delivery of optimum health care, patients’ compliance to therapy, follow up care and ultimately treatment outcomes. Few studies done to evaluate the impact of language barrier on cancer treatment outcomes indicate that there is limited information shared between providers and patients even when interpreters are engaged due to difficulties in direct communication between the two parties.52,53,54 The impact of patient and provider communication and the role of medical interpreters in cancer treatment and outcomes need to be explored further in future studies.
The study has several limitations. Data for this study were obtained from SEER and the supplementary Specialized Census Tract-level SES and Rurality Database which provides information on the overall SES of the census tract of residence of a patient and not the SES of the patient.25,26 Only information on the insurance status of patients diagnosed from 2007 – 2015 was available, hence the influence of insurance on treatment outcome was not assessed in this study. Additionally, Asians, American Indians, and cases without racial identity were grouped together due to their small sample sizes, which does not allow for good representation of the independent survival outcomes of Asians and American Indians. Treatment information in SEER is incomplete with no clear differentiation between cases who did not receive treatment and those whose treatment information is missing, making it difficult to infer real differences in treatment among the racial groups. SEER does not have information on molecular tumor markers or genomic ancestry which may influence the racial disparities in outcome.55,56,57 Finally, the data do not include patients’ choice in the treatment.