Health disparities, including those related to cancer, have many causes, occurring at the levels of individuals, institutions, and communities. Cancer incidence and mortality vary by traditional measures of socioeconomic status (SES) such as income and education, and because of the strong correlation between race/ethnicity and SES, it is a major challenge to separate the effects of race from those of SES on cancer-related outcomes. Nonetheless, blacks experience disproportionate cancer mortality compared to non-Hispanic whites, even in affluent communities. Race remains a risk factor for cancer-related outcomes even after controlling for poverty.[1] This raises several general questions and explanations: (1) What are the relevant environmental—including social-exposures that vary by race/ethnicity? (2) By what mechanisms, including gene-environment interactions, do these exposures contribute to disparities? (3) What mediates the observed disparities?

Individuals from racial and ethnic minority groups present with cancer at a later stage and survive with cancer for a shorter duration than non-Hispanic whites. However, racial/ethnic differences in cancer incidence are smaller than the gap in mortality rates. This suggests that following the diagnosis of cancer, individuals from minority groups receive less effective care than non-Hispanic whites, through available health-care systems and their social support networks. For this reason, much of the literature on cancer disparities has focused on health-care disparities (ie, disparities in the delivery of preventive and therapeutic care).

Complex Web of Contributing Factors

In this issue of ONCOLOGY, Raghavan provides a review of health-care disparities as the basis for racial disparities in cancer detection and survival.[2] He is careful to discuss race as a social construct that is associated with socioeconomic disadvantage, and suggests consideration of the gap in cancer incidence and survival in the context of social exposures that may modify disease status and/or disease outcomes. This article illuminates what is known about cancer care disparities, and describes current gaps in knowledge and future directions for research in this setting.

The author explains many of the contributing factors, at the level of individuals, health-care providers, communities, and public policy. He also draws out the complex web of origin of these disparities in cancer prevention, diagnosis, and treatment. In describing the sources of cancer care disparities, he first mentions "minority community suspicion," or lack of trust, as a contributing factor. Trust is indeed a key barrier to adherence to cancer care in general, including acceptance of participation in clinical trials.[3]

Raghavan appropriately suggests that contextual factors contribute to health-care disparities through their effects on exposure to socioeconomic disadvantage and lack of social support. While contemporary cancer prevention and treatment approaches tend to be targeted to individual patients, innovations in cancer care are most likely to be adopted by individuals who have the means and feel empowered to do so. If we assume that on average such innovations are likely to benefit individuals irrespective of race or ethnicity, and more likely to be adopted by more affluent groups, then their differential rate of implementation may increase health disparities on the basis of socioeconomic disadvantage. Further, because of the association between socioeconomic status and race, this may translate into a racial disparity. Therefore, it is critical that health-care providers understand and address the contextual barriers faced by their patients, as a means for promoting adherence to recommended care.

Gene-Environement Interactions

The author indicates that "there are real differences in the biology of cancer and of response to treatment in different populations, based on differential gene expression...." While this is a plausible hypothesis, there remains a lack of evidence on the relative contribution of biologic differences to disparities in cancer-related outcomes. Racial differences in cancer mortality potentially reflect differences in incidence, or differences in survival following the diagnosis of cancer. Evidence suggests that racial and ethnic minority populations bear a disproportionate burden of exposure to environmental carcinogens in their residential communities—especially in racially segregated communities[4] and in the workplace.[5]

Carcinogenesis is a multistep process that features the interaction between genes and relevant environmental carcinogens. The increasing availability and progressively reduced cost of high throughput genotyping techniques has strengthened studies of gene-environment interactions, and facilitated use of ancestry-informative markers as a means of quantifying the extent of admixture of genetic material from different geographic origins (eg, Africa vs Europe) in individuals and in populations.

Transdisciplinary Approaches