According to a pooled analysis of 18 prior studies, sex hormones in the bloodstream appear not to be linked to prostate cancer risk. The researchers found no association between circulating levels of different forms of testosterone or estrogen and prostate cancer risk.
The analysis is published in a new study in the 29th January issue of the Journal of the National Cancer Institute and was conducted by Dr Andrew Roddam of the University of Oxford, England, UK and colleagues at the Endogenous Hormones and Prostate Cancer Collaborative Group.
There have been nearly two dozen studies on the link between circulating levels of androgens or sex hormones, and the risk of prostate cancer, but on the whole the results are inconsistent, said the researchers.
Roddam and colleagues analyzed pooled results from 18 studies that between them covered existing worldwide epidemiologic data about the relationship between serum (blood) levels of sex hormones and prostate cancer. The data included 3,886 men who had prostate cancer and 6,438 men who did not (controls).
The results showed:
- No links between risk of prostate cancer and serum levels of testosterone, calculated free testosterone, dihydrotestosterone, dehydroepiandrosterone sulfate, androstenedione, androstanediol glucuronide, estradiol, or calculated free estradiol.
- Serum levels of sex hormone-binding globulin were “modestly inversely associated with prostate cancer risk”.
- There was no statistical evidence of heterogeneity among the studies and adjustment for potential confounders made little significant difference to the results (both of which strengthen the case for the findings of this study).
The researchers concluded that:
“In this collaborative analysis of the worldwide data on endogenous hormones and prostate cancer risk, serum concentrations of sex hormones were not associated with the risk of prostate cancer.”
The potential limitations of the study were listed as: inadvertent bias from the long time it takes for prostate cancer to manifest (some controls could have had it without knowing), different laboratory methods used to measure serum hormone levels, and the fact only one serum sample was taken per subject.
In an editorial accompanying the study, Dr Paul Godley and colleagues at the University of North Carolina at Chapel Hill, US, praised the collaborative effort of the researchers and said these results should now help to shift the focus of prostate cancer research:
“The study obliges the scientific community to move past a seductive, clinically relevant, and biologically plausible hypothesis and get on with the difficult task of exploring, analyzing, and characterizing modifiable risk factors for prostate cancer,” they wrote.
Prostate cancer is the fifth most commonly diagnosed cancer worldwide, with around 680,000 new cases a year (2002 figures). In the US there were an estimated 218,890 new cases last year, and 27,050 deaths.
“Endogenous Sex Hormones and Prostate Cancer: A Collaborative Analysis of 18 Prospective Studies.”
Endogenous Hormones and Prostate Cancer Collaborative Group.
Journal of the National Cancer Institute Advance Access published on January 29, 2008.
DOI: 10.1093/jnci/djm323
Sources: NCI press release, journal abstract and editorial, NCI and Cancer Research UK websites.
Written by: Catharine Paddock, PhD