Race, obesity, and risk for prostate cancer


By using data from the prospective SELECT trial (the Selenium and Vitamin E Cancer Prevention Trial, conducted between 2001 and 2011), researchers have been able to suggest that obesity is strongly associated with increased risk for prostate cancer diagnosis among African American males compared to non-Hispanic whites.

Barrington et al. have just published their findings in JAMA Oncology.

It is well known that African American men have much higher rates of prostate cancer incidence and mortality than men in any other ethnic group here in the USA.

Barrington and her colleagues set out to explore whether the suspected association between obesity and risk for prostate cancer risk differs between African American and non-Hispanic white men and whether obesity modifies the excess risk among African Americans. To do this, they re-analyzed available data on 3,398 African Americans and 22,673 non-Hispanic whites who participated in the SELECT trial. (Regular readers will remember that this large, randomized, prospective trial showed no benefit from the use of either selenium or vitamin E in the prevention of risk for prostate cancer.)

Here are the key findings from their study:

  • Median patient follow-up was 5.6 years.
  • During this follow-up period, there were diagnoses of
    • Low-grade prostate cancers (Gleason score < 7) in
      • 148/3,398 African Americans (4.35 percent)
      • 898/22,673 non-Hispanic whites (3.96 percent)
    • High-grade prostate cancers (Gleason score ≥ 7) in
      • 88/3,398 African Americans (2.59 percent)
      • 441/22,673 non-Hispanic whites (1.95 percent)
  • Overall risk for diagnosis of prostate cancer (compared to the risk for diagnosis among non-Hispanic white men with a BMI < 25) was
    • Not increased among non-Hispanic whites with a BMI ≥ 35 (hazard ratio [HR] = 0.94)
    • Significantly increased among African American men with a BMI < 25 (HR = 1.28)
    • Significantly increased among African American men with a BMI ≥ 35 (HR = 2.03)
  • Risk for diagnosis with low-grade prostate cancer associated with BMI was
    • Negative among non-Hispanic white men with a BMI of ≥ 35 as opposed to < 25 (HR = 0.80)
    • Positive among African American men with a BMI of ≥ 35 as opposed to < 25 (HR = 2.22).
  • Risk for diagnosis with high-grade prostate cancer associated with BMI was
    • Positive among non-Hispanic white men with a BMI of ≥ 35 as opposed to < 25 (HR = 1.33)
    • Positive among African American men with a BMI of ≥ 35 as opposed to < 25 (HR = 1.81)

Barrington et al. conclude that:

Findings from this study suggest that increased obesity could partially explain the substantially higher risk of prostate cancer among [African American] men. Not only is obesity more strongly associated with increased prostate cancer risk among [African American] men, it is considerably more prevalent among this group.

However, it is important to note the use of the word “could” in this conclusion, and it may be hard to tease out exactly what this association between BMI and risk for prostate cancer among African American males is telling us. Could it have something to do with the genetic make-up of African Americans? All we can really say at present is “maybe”. It could also have something to do with significant differences in diet or other factors. It should also be noted that limitations of the available study data need to be taken into account, and we should be very cautious about the interpretation of these data until they can be confirmed by other findings.

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