Numerous studies utilising population-based databases have uncovered racial, ethnic, and socioeconomic inequities in ovarian cancer care and treatment access [7, 15,16,17]. Our goal in the current study was to assess risk of EOC mortality using data from patients treated in the Military Health System where access to healthcare is universal. We observed that there were no differences in EOC survival between White patients and Black patients. Notably, Asian patients had a lower mortality risk compared with White patients.

Our observation of no difference in survival between White patients and Black patients in a Military Health System contrasts with a previous report using SEER data from 1995 to 2015 which showed that Black EOC patients were at higher risk of all-cause mortality (HR 1.28, 95% CI 1.23–1.33) than White patients in models that were adjusted for age at diagnosis, stage, grade, subtype, surgical intervention, chemotherapy, radiation, laterality, insurance status and SEER registry region [18]. In the most recent US cancer statistics report using SEER data, the 5-year relative survival rate for Black women with EOC was the lowest (41%) compared to White women (49%) [1]. Albain et al. [19] similarly observed a 10-year survival rate of 13% for Black women versus 17% for all other patients with advanced stage (Stage III or IV) ovarian cancer using data from randomised clinical trials patients of the Southwest Oncology Group. In contrast to the observed disparities in survival reported for Black women with EOC using general population data, our findings using data from the Military Health System support the idea that survival disparities could be largely influenced by access to healthcare.

We observed that Asian patients had a lower mortality risk compared with White patients. This result was consistent with the Fuh et al. [3] study using SEER data, where it showed that the 5-year disease-specific survival of Asian patients with EOC was higher compared to White patients (59.1% vs. 47.3%, respectively, P = 0.001). In a meta-analysis of EOC patients who enrolled in 10 Gynaecologic Oncology Group clinical trials there was a similar improvement in disease-specific survival in Asian patients (N = 273) compared with White patients (N = 7641) (Asian compared with White patients, HR 0.84, 95% CI 0.72–0.99) after accounting for age, body mass index, better performance status, stage, histology, grade and residual disease [20]. This study did not include other racial and ethnic groups.

The current report showed differences in the distribution of histological subtypes across racial and ethnic groups. Specifically, Asian cases had the highest proportion of clear cell EOC (10.5%) compared with ≤7.1% in other groups. This finding is consistent with a report from Park et al. who observed that a higher proportion of Asian EOC patients were diagnosed with clear cell tumours (11.7%) than other racial and ethnic groups (clear cell tumours ranging from 2.4% to 4.5%), with Black women the least likely to be diagnosed with clear cell EOC (2.4%) [4]. We found that the proportion of serous tumours was highest among White, Black and Hispanic patients (≥ 56%), followed by Asian (49.7%) and Pacific Islander (42.1%) patients. A prior study also found serous cases to be the least frequently diagnosed among Asian women, while White and Black women had equivalent proportions of serous EOC diagnoses [4]. Considering that treatment techniques are not uniformly effective across EOC histotypes [21,22,23], variations in histologic subtype distribution by race may contribute to racial and ethnic survival differences. We accounted for differences in histologic subtype proportion by adjusting for histology in the multivariable models.

The standard recommended treatment for ovarian cancer by the National Comprehensive Cancer Network (NCCN) is cytoreductive surgery along with platinum- and taxane-based chemotherapy [24]. Eaglehouse et al. showed that Asian women were > 2 times as likely to seek NCCN guideline-based care than White women in a recent study employing ACTUR data as well as the Military Health System Data Repository administrative claims data [6]. In our study, we found that 79.0% of Asian patients underwent both surgery and chemotherapy, compared to 71.9% of patients in other racial and ethnic groups. Importantly the improvement in survival among Asian individuals was still apparent when we restricted the analyses to cases who received uniform treatment (chemotherapy and surgery). This result suggests that factors other than receipt of treatment may explain the improved survival in Asian EOC patients. It was suggested that women with BRCA germline mutations have higher response rates to both platinum- and nonplatinum-based regimens than mutation-negative patients [25], and certain Asian groups were found to have a higher predisposition to BRCA mutations such as the Chinese women from Hong Kong and Korea [26, 27]. BRCA mutation status was not available in the current study. It will be of interest to consider BRCA mutation status (germline and tumour somatic mutations) in future studies focusing on racial and ethnic differences in EOC survival.

Our study had several strengths, including the ability to evaluate EOC overall survival in a DoD Military Health System with equal access to free medical care. Another strength was that we included Pacific Islander and Hispanic EOC patients who have not been included in earlier studies focusing on EOC survival. There are also some limitations of this study including the lack of information on treatment data beyond the first primary treatment. We also lacked information on the cause of death however we anticipate that our results for all-cause mortality will be mostly congruent with findings for EOC-specific death, given that EOC is a highly aggressive disease, and consequently the majority of deaths in this patient cohort will be attributable to EOC or its sequelae. It is possible that some women who are diagnosed in the military, and tracked by the ACTUR registry, received some of their care outside the military health system, including some academic facilities. This could explain why data on the first course of treatment (< 5%) were missing. In the ACTUR database, there were three methods of race and ethnicity reporting; two of the methods were based on self-report from the patient while the third method involved physician reports. Physician-reported race and ethnicity is less reliable than self-reports from the patients themselves. This could lead to misclassification of race and ethnicity and may attenuate risk estimates towards the null value. Our study included TRICARE recipients inside the Military Health System, which may not be representative of the racial and ethnic composition of the overall United States population. Although our study was large, the number of patients did not allow further subgroup stratification (e.g., consideration of Chinese, Korean, Filipino subgroups). SEER statistics indicate that Asian subgroups have varying 5-year ovarian cancer survival rates, ranging from 62.1% for Vietnamese to 48.2% for Asian Indian/Pakistani [3].

In summary, uneven access to care is hypothesised to play a significant role in the observed racial and ethnic disparities in EOC survival rates. Thus our goal was to determine if race and ethnicity are associated with variations in EOC survival in a military population with equal access to healthcare. With the exception of a slight survival advantage for Asian patients, we observed no racial or ethnic differences in EOC survival for Black, Pacific Islander and Hispanic patients as compared with White patients. These results underscore the need to investigate how differences in access to healthcare may influence observed racial and ethnic disparities for EOC.