Effect of neighborhood deprivation index on breast cancer survival in the United States

Our study focuses on locoregional BC as its treatment requires access to health care systems that are less available in underprivileged neighborhoods. In our study, we found that the deprivation index of the neighborhoods was in significant association with BC survival. Our analysis showed that the OS and DSS of patients with locoregional BC were lower for those who live in socioeconomically underprivileged neighborhoods compared to those who live in affluent neighborhoods. The survival differences were observed among all subtypes of BC. The differences in survival persisted even after adjusting for demographic, clinical, and treatment factors that could affect BC survival. On multivariate analysis, the mortality difference among the patients living in different socioeconomic areas was statistically significant within the overall cohort, HR + and HER2 + BC subtypes, but not within the TNBC subtype. This could be explained by the aggressive nature of TNBC. As TNBC is very aggressive and has high relapse rate [18], the survival of patients with TNBC could be poor regardless of their socioeconomic status.

Understanding the impact of neighborhood deprivation on BC survival will facilitate the development and implementation of policies and prioritize investments in communities with high deprivation scores. This could improve the socioeconomic conditions which could eventually improve clinical outcomes [19]. Several factors in the neighborhood influence the health of an individual directly, as well as indirectly: poverty, access to the health care system, transportation system, housing quality, unemployment, environmental pollution including air and water pollution, neighborhood hygiene, waste management system, crime rates, racial composition, educational system, tobacco availability and marketing, access to healthy food [20‐23]. These along with the factors that affect the individual such as marital status, family/social support, co-morbidities, mental health, nutritional status, healthy lifestyle, insurance status, and educational status play an inevitable role in the survival outcomes of malignancies. Studies have shown that prolonged and cumulative exposure to the above-mentioned deprivation-associated stressors can induce chronic inflammation which is one of the etiologies behind cancer development [24, 25]. Therefore, a proper understanding of the deprivation factors of an individual and their neighborhood is essential to plan interventions to reduce the burden of cancer mortality.

Our study adds to the existing literature in multiple ways. This study is the first to our knowledge to use a national database to examine the association between neighborhood deprivation with the clinical outcomes of locoregional BC; most prior studies used regional databases. Prior studies showed racial disparities in BC-related outcomes in the US and minoritized groups tend to have higher BC-related mortality [22]. In a study by Luningham et al. which examined the association between racial disparities and SES in BC survival between Black and White women across Georgia, it was found that Black women with BC had higher mortality than White women, but this disparity was not explained by the socioeconomic deprivation of their residential area. White patients living in socioeconomically affluent areas had lower rates of BC mortality compared to those who reside in underprivileged neighborhoods [26]. We observed similar results in our study: We observed similar results in our study. White BC patients living in socioeconomically underprivileged areas had higher mortality compared to Whites living in socioeconomically affluent areas. However, this difference in the mortality was not observed among Black BC patients. This is an interesting finding that may need validation in future studies. This difference leads us to speculate that irrespective of area of residence, Black breast cancer patients continue to have worse outcomes. This may be either due to cultural factors precluding Black patients to seek healthcare, mistrust for the system, lack of insurance, or could be due to inherent aggressive disease that even with access to the above facilities, the natural biology of the disease continues to be aggressive [27]. This clearly highlights the need for both better treatments for Black patients as well as more attention at a policy level for Black patients.

Our study finding critically shows the important role of area of residence on clinical outcomes, and thus emphasizing that socioeconomic factors of the neighborhood play a vital role in determining clinical outcomes. There were several studies conducted to understand the reason behind the observed racial disparities. One of them was attributed to poor neighborhoods. Black and Hispanic women are more likely to live in poor neighborhoods and Black patients were found to live in neighborhoods with high poverty rates and this difference persists even after adjusting for their income status [28]. In our study, we found that Black and Hispanic women with BC were more commonly residing in the underprivileged neighborhoods compared to socioeconomically affluent neighborhoods; however, the disparities in BC-related mortality of the patients from these socioeconomically different neighborhoods was not observed among Black patients and persisted even after accounting for the racial disparities.

Similarly, patients without insurance were found more commonly in the underprivileged neighborhoods and those neighborhoods had more rural areas. Advanced BCs (higher stage and grade) and aggressive BC such as HER2 + and TNBC were predominantly found in the underprivileged neighborhoods compared to the affluent neighborhoods. In our study, BC patients from affluent neighborhoods received more surgical and radiation treatments which can be explained by the higher percentages of urban areas in these regions with better facilities for treatments, and better referral systems. In a study by Fwelo et al., it was found that Black and Hispanic women were more likely to undergo mastectomy compared to Whites [29]. This discrepancy could be attributed to the fact that breast cancer is often diagnosed when locally advanced in Black women, indicating limited access to early detection through adequate screening and precluding lumpectomy [27, 29]. Additionally, cultural preferences, low healthcare literacy, and transportation barriers may contribute to limited healthcare access, potentially influencing the decision to avoid radiation treatment [27, 30]. Our study showed that in the overall BC cohort, patients who received chemotherapy were slightly higher in the underprivileged neighborhoods than in the affluent neighborhood. One possible explanation for this is that the advanced diseases that requires chemotherapy was more prevalent in the underprivileged neighborhood regions. This could also be attributed to several other factors, such as low healthcare education, leading to misconceptions about medical information, as well as limited access to tests (due to insurance issues) that predict the benefits of adjuvant chemotherapy, like the Oncotype DX 21-gene expression assay, which can potentially result in overtreatment among racial minorities [27, 31]. Nevertheless, the disparities in BC-related mortality remain unaffected when adjusted for the demographic, clinical, pathological, and treatment-related factors such as age, race, stage, grade, insurance, surgery, radiation, and chemotherapy. This suggests that additional factors related to neighborhood SES that are not captured by the NDI play an important role in BC-related outcomes. The access to genetic and somatic testing which are important for deciding the appropriate treatments in BC might be limited to patients from poor neighborhood which could have impacted their survival.

Poverty, unhealthy food habits, decreased access to healthy food, environmental pollution, increased advertising of tobacco in poor neighborhood leads to increased incidence of various cancers in patients from these neighborhoods [20, 21, 23, 32, 33]. Furthermore, the transportation barriers, decreased access to better comprehensive cancer centers with standard of care treatments or novel clinical trials, poor nutritional and educational status of patients, financial toxicity associated with cancer treatment leads to increased cancer-related mortality in socioeconomically poor neighborhoods [11, 15, 34, 35]. In addition to this, poor environmental hygiene and pollution can add to the increased mortality by causing infections in cancer patients who are already immunocompromised due to cancer and associated treatments [36]. In a patient-reported outcomes study in advanced cancers, it was found that patients from socioeconomically underprivileged areas have a higher level of anxiety [37]. Factors such as anxiety, depression, and poor social support which are subjective measures of poor mental health are not accounted for in any of the tools to measure the neighborhood/individual SES and have been shown to be associated with cancer-related mortality [14, 37, 38]. Disparities in BC survival related to neighborhood SES reflect the systematic barriers in policies related to health care, education, employment, insurance, environment, and judicial system. Our study findings may support restructuring the policies, to implement new policies and investments in socioeconomically underprivileged neighborhoods which would help to decrease inequalities in opportunities, improve healthcare facilities, and increase access to timely cancer treatments.

Our study has many strengths and certain limitations. We used large real-world data to assess the impact of neighborhood deprivation on clinical outcomes of BC patients. These data capture more than 50% of the US population, and therefore, the results are generalizable. We adjusted for multiple factors that are known to influence survival, including racial distribution, demographic factors, clinicopathological factors of the disease [39]. Although NDI is a comprehensive tool to assess socioeconomic disadvantage, it may not capture all the factors associated with neighborhood SES. We could not assess the influence of several neighborhood factors that may contribute to the mortality of BC such as access to transportation, environmental: air, water pollution, poverty level, accessibility to healthy food, and crime rate of the neighborhood. As we do not have one comprehensive tool to assess the socioeconomic status of neighborhoods and individuals together, future studies warranting the combination of multiple indices such as area deprivation index, Yost index might be beneficial. As it is a retrospective national database study, several individual factors that can affect the mortality rates of BC such as comorbidities of patients, social support, details of factors such as anxiety, and depression that can affect the mental and physical condition of the patients were not collected. Incompleteness of individual-level data collected on cancer risk and treatment, and incomplete values for several variables collected from multiple registries were other limitations. Further tumor recurrence data, specific details on the type, dose, and duration of chemotherapy, radiation, oral chemotherapy, targeted agents were not available in the SEER database and these factors could have been associated with the mortality of BC.

Moving forward, it is crucial for professional societies and cancer institutes to take the initiative to design strategies that address breast cancer disparities stemming from the socioeconomic status of neighborhoods. Some potential initiatives include identifying underprivileged areas in communities and providing additional facilities to these patients, such as offering free transportation and, organizing mobile units equipped with imaging technologies to visit underprivileged areas regularly. Additionally, addressing the climate gap through federal support to rebuild infrastructure, reduce sources of pollution, and ensure accessible and affordable clean energy sources can be another strategy to alleviate economic injustice [40]. Restructuring the health system to address the racial wealth gap, promoting equity and inclusion by ensuring adequate access to clinical trials for everyone, supporting research focused on preventing and treating aggressive breast cancer subtypes (more prevalent in racial minorities, such as Blacks), and ensuring universal access to healthcare, are key strategies that can be adopted to decrease healthcare disparities and reduce mortality rates from breast cancer [5, 41, 42].