As I noted last week, I have not written much about prostate cancer as I find the information and data about this cancer difficult to sift through, but since we opened the door last week, I suppose I can add a few articles on this disease, given how important it is.

So for this week’s article, let us focus on racial disparities in prostate cancer. In truth, we do not really know a lot in general about risk factors for prostate cancer—they are not as salient for prostate cancer as they are for breast cancer or some other cancers. But certainly the characteristic that stands out is racial differences. While the world of cancer research and cancer policy is obsessed with racial disparities in cancer incidence and outcomes, we really should look more closely at what these disparities truly are. If one utilizes mortality or survival as the outcome metric, then it is certainly the case that there is hardly a cancer site for which Blacks do not do worse than Whites. Across the board, this generally reflects inferiority in access to care—worse doctors, worse hospitals, delayed diagnosis, concomitant worse treatment, etc. These problems and differences are generally the result of sociocultural and socioeconomic problems that Blacks have from their backgrounds or their current residential or other circumstances.

But what about incidence? Again, there are a few disparities in cancer incidence that arise from differences in lifestyle or occupation between Blacks and Whites—differences in tobacco and other inhaled exposures and lung cancer, HPV and anogenital cancer, obesity and endometrial cancer, for example.

But what about actual innate biological differences between Blacks and whites? In that category there only appear to be two clearcut candidates—prostate cancer and multiple myeloma. Blacks have something over twice the prostate cancer mortality rate of whites in the U.S. On the other hand, the incidence rate is about 60% higher among Blacks than whites in the U.S. Some of this may reflect differences in PSA (prostate-specific antigen) screening rates but this seems to be pretty replicable. And as I noted above, the worse mortality difference reflects in large part access to care.

Differences in incidence can reflect either environmental exposures or innate biological differences, like genes. In the past, this Black-White difference was believed to be reflective of environmental exposures, such as dietary or other lifestyle differences between Blacks and Whites. This was largely due to the fact that the observed prostate cancer rates in Africa itself were thought to be low.

However, improved cancer registries in many of the low-resource sub-Saharan countries have demonstrated that the prostate cancer incidence rates in Africa are indeed elevated and reflective of the Black African population present. Likewise, several of the Caribbean countries (Trinidad-Tobago, Cuba, Barbados, Jamaica) also had high incidence rates reflective of the high prevalence of admixture of African blood in their populations. Thus, the fact that prostate cancer rates are elevated across men of African descent irrespective of their geographic location—sub-Saharan Africa itself, the U.S., various Caribbean islands, Brazil—suggests that it would be nearly impossible to identify a lifestyle or environmental exposure that they would all share that could account for the elevated incidence rates. Instead, we must conclude that there are genes—presumably single nucleotide polymorphisms or otherwise—that are passed down from one generation to the next and that migrate along with the individual’s skin color.

Indeed, studies have been conducted in order to estimate the degree of admixture of African blood (or more precisely genes) present in populations of varying origins. In other words, when African slaves were brought to the New World, they interbred with populations present in the region they were brought to, and these genetic prevalences have been brought down to the present time. Studies have explored the degree of African ancestry present in populations of differing ancestry. To a great degree, the skin pigmentation of these populations are reflective of the African admixture. Thus, the average U.S. African-American is approximately 50-73% genetically of African ancestry. Nigerians approach 100%, while Jamaicans were 89%, and Puerto Ricans had an admixture of 27%. Thus, the average darkness of the skin among these groups is consistent with these figures.

For our purposes here, the increase in prostate cancer risk in each of these populations of African origin also parallels to some degree the proportion of African genes in the population. So the race-associated disparity in prostate cancer risk appears to be due to genes that were brought with the slaves to the Western Hemisphere in the 16th and 17th centuries. Studies are ongoing to attempt to identify the genetic markers or mutations at play in prostate cancer risk, but the main culprits remain, for the moment, at large.

The racial disparities for prostate cancer are active, therefore, for both incidence and mortality, as well as in terms of stage at diagnosis and grade at diagnosis. Interestingly, there appears to be a concomitant decreased risk among Asians and Hispanics.

Alfred I. Neugut, MD, PhD, is a medical oncologist and cancer epidemiologist at Columbia University Irving Medical Center/New York Presbyterian and Mailman School of Public Health in New York. Email: [email protected].

 This article is for educational purposes only and is not intended to be a substitute for professional medical advice, diagnosis, or treatment, and does not constitute medical or other professional advice. Always seek the advice of your qualified health provider with any questions you may have regarding a medical condition or treatment.