Cancer death rates continue to decline in the United States and other countries. This can be attributed to decades of research advancing disease prevention and cancer therapies. However, though many have benefited from these advancements in cancer care, disparities in cancer risk and outcomes persist, disproportionately affecting underserved and minority groups. Prostate cancer is a compelling example. In the United States and England, men of African descent continue to have 2-3 times higher rates of fatal disease than other men.
Cancer disparities are largely explained by health care disparities, lifestyle factors, cultural barriers, and disparate exposures to carcinogens but, even when these are accounted for, some of the cancer disparities stubbornly persist. To address this challenge, investigations should expand into both neglected and emerging research areas with the aim to further reduce disparate outcomes. As an example, the impact of the microbiome, comorbidities, chronic stress, and ancestry-related risk factors on tumor biology remains understudied. Thus, there are still opportunities with health disparity research to discover previously unrecognized risk factors to advance cancer prevention and treatment.
Comorbidities in cancer patients are chronic diseases that commonly occur with cancer because of shared risk factors. Some chronic diseases contribute themselves to premature deaths in disadvantaged populations, with obesity, diabetes, and hypertension conferring an excess mortality risk to Native Americans and African Americans. Additionally, comorbidities can influence cancer diagnosis, tumor biology, and the risk of metastasis and lethal cancer. Cancer patients with a comorbidity are generally less likely to receive curative cancer treatments. With the higher prevalence of comorbidities in underserved and minority populations, one would predict that they contribute to a disproportionate cancer burden in these communities. Thus, comorbidities should be moved to the forefront of cancer health disparity research—with a focus on mechanisms linking comorbidities to an adverse tumor biology and cancer survival. Cancer deaths due to comorbidities are preventable with treatment of the comorbid condition and lifestyle changes among other intervention strategies.
Comorbidities also tend to be exclusionary for participation in clinical trials with discussion and offer of trial participation by clinicians being less likely. Clinical trial participation of US minorities remains low. Historical mistrust of underserved populations to the medical profession and a higher prevalence of comorbidities in these populations prevents access to trials which may improve cancer outcomes for participants and increase our knowledge about who may or may not benefit from a novel cancer therapy. Therefore, changes in the guidelines for clinical trial participation are urgently needed to assure that therapy efficacy is assessed in populations of diverse backgrounds and among those who have developed chronic comorbid conditions.
“changes in the guidelines for clinical trial participation are urgently needed to assure that therapy efficacy is assessed … among those who have developed chronic comorbid conditions”
Exposure to carcinogens define the mutational burden of tumors and their biology. Lack of biospecimens from minority populations in research studies such as whole genome sequencing of tumors has prevented these patients from receiving the full benefit of a personalized medicine approach developed from genomics research. Recent trials highlighted the effectiveness of immunotherapy in patients with advanced cancers. Yet, because these studies are being carried out predominantly in patients of European descent, the value to other populations remains unclear. There is evidence that gender and ancestry may affect immune therapy responses. Despite this knowledge, data on the immune response for minority populations remain sparse across different cancer types.
The research community, with the support of the Legislature, has responded to the recognized lack of population diversity in research studies. Under the Precision Medicine Initiative, the National Institutes of Health have embarked on the “All of Us” initiative, which, as the largest longitudinal study in the history of the US, aims to create a centralized national database of health data and biospecimens from 1 million volunteers. A cornerstone of this study is the enrollment of racial and ethnic minorities to ensure that diversity can inform precision medicine research.
The Patient Protection and Affordable Care Act was signed into law in 2010. Its primary goal was to improve health insurance coverage as unequal access to health care is a fundamental driver of cancer disparities. While there have been modest decreases in the percentage of uninsured patients following Medicaid expansion and modest increases in cancer screening, future analyses should provide more clarity as to what extent this Act may reduce or eliminate cancer survival health disparities in low-income communities and across race/ethnic groups.
Recent findings on disparities in COVID-19 outcomes across underserved populations has brought health inequity back to the forefront. Researchers should capitalize on the renewed interest in health disparities to finally close the cancer disparities gap and allow all to benefit equally from the medical advances that have been hard fought to achieve. We suggest that comorbid chronic diseases, chronic stress exposure, and population differences in immune response are candidate causes of cancer health disparities that should be examined with future research.