Epidemiology, genetics, and risk for (aggressive) prostate cancer


A couple of papers presented in the past few days at meetings of the American Association for Cancer Research (AACR) and the American Society for Human Genetics (ASHG) provide us with interesting (if potentially confusing) information about risk for a diagnosis of prostate cancer.

On the one hand, in a presentation at an AACR meeting in National Harbor, Maryland, Su et al. reported — based on data from 1,083 European-American and 1,049 African-American men who had recently been diagnosed with prostate cancer — that there was an association between the following long-term occupations and an increased risk for aggressive forms of prostate cancer (compared to those who worked in education):

  • Truck driving
  • Working at a garden shop for at least 6 months
  • Construction workers
  • Working in the financial industry (e.g., accountants)

On the other hand, there was no apparent increase in risk for those with occupations like

  • Exterminator
  • Landscaper
  • Animal caretaker

(In this study, the authors defined “aggressive” prostate cancer as any cancer that was initially diagnosed with a PSA level > 20 ng/ml, a Gleason sum of 8 to 10, or a combination of a Gleason sum of at least 7 and a clinical stage of T3 or T4.)

While there is a hypothetical argument for why truck driving is associated with an elevated risk for diagnosis with aggressive forms of prostate cancer, what The “New” Prostate Cancer InfoLink thinks that this study really shows is the potential dangers implicit in thinking that epidemiological “associations” like this necessarily have anything at all to do with cause and effect. (For more details on this presentation by Su and his colleagues, please see articles in The Huffington Post and The Los Angeles Times.

In contrast, a paper presented at the annual meeting of the ASHG in Boston by a group of Scandinavian researchers suggests that the “heritability” of prostate cancer (i.e., the degree to which genetics contribute to risk) was 58 percent, and this is the highest heritability factor for any of the 10 types of cancer included in their study. (Please note that this heritability estimate is for cancers of any degree of aggressiveness, not just the most aggressive types)

This second paper (by Kaprio et al.) was based on an analysis of data from 133,689 monozygotic (identical) and dizygotic (fraternal) pairs of twins collected as part of the Nordic Twin Registry of Cancer. In this case, additional information can be found on the Medscape Oncology web site. Specifically, Kaprio and his colleagues report that a man whose identical twin has prostate cancer has a 32 percent risk for prostate cancer himself, whereas a man whose fraternal twin has prostate cancer has a 16 percent risk.

Commenting on this second study, Richard Stevens, PhD, of the University of Connecticut Health Center in Farmington, Connecticut, notes that it brings up interesting questions about the way in which genetic and environmental factors may combine to modify risk for specific forms of cancer. Dr. Stevens is quoted as follows:

It’s a very strong study. The exciting thing about this study with prostate cancer is that it’s certainly saying something about mechanism that we don’t get.

For comparative purposes, the table below shows the “heritability” of prostate cancer compared to other cancers studied by Kaprio and his colleagues:

HertabilityPIC

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