Serum triiodothyronine is increased in men with prostate cancer and benign prostatic hyperplasia

Triiodothyronine is the active thyroid hormone produced by de-iodination of the precursor thyroxine that is necessary for the growth of prostate cancer cells in vitro. For this reason we assessed serum triiodothyronine levels in men with localized prostate cancer, benign prostatic hyperplasia (BPH) and controls in the same age group.

We studied 161 men referred for treatment of localized prostate cancer, 20 with BPH and 27 controls. Serum triiodothyronine was determined by fluorometric immunoassay and a commercially available instrument.

Men with BPH had the highest triiodothyronine levels, followed by those with prostate cancer. Controls had the lowest triiodothyronine. There was significant triiodothyronine variation among the 3 groups (1-way ANOVA p = 0.001). In men with BPH serum triiodothyronine was significantly different from that in men with prostate cancer (Tukey's multiple range test p = 0.013). Men with prostate cancer had serum triiodothyronine that was significantly different than in controls (p = 0.048), as did those with BPH (p <0.001). Because serum triiodothyronine normally decreases with age, we performed multivariate analysis of variance controlling for age. There was a significant decrease in serum triiodothyronine with age (p = 0.020). There was also significant triiodothyronine variation among the 3 subject groups independent of age (p <0.001).

Urologists are actively seeking additional biomarkers of prostate cancer aggressiveness. Many prostate cancers are quite indolent and may never cause a problem but it is impossible to identify such tumors with certainty. With more and better biomarkers many older men with prostate cancer may be spared the rigors of radiation therapy and/or surgery as well as complications. Triiodothyronine may be such a biomarker. Also, new prostate cancer and BPH therapies may be directed toward inhibiting the mitogenic effects of triiodothyronine.