Does TRT Cause Prostate Cancer? What 80 Years of Research Actually Shows
The year was 1941, and a researcher named Charles Huggins made an observation that would shape medical thinking for the next eight decades and counting.
He took men who had advanced prostate cancer, castrated them to remove their testosterone, and watched their cancer markers fall. Then he gave testosterone back to those castrated men and watched the markers rise again. The medical community looked at that sequence and drew what seemed like an obvious conclusion: if removing testosterone helps, then adding it must cause harm. Huggins won the Nobel Prize in 1966 partly on the strength of this work, and the belief calcified into medical doctrine.
The problem is that the logic only holds under one very specific condition that almost no man on testosterone replacement therapy ever experiences.
To understand why, you need a quick map of how the prostate actually responds to testosterone. The prostate, like most tissues that respond to hormones, does not have an unlimited appetite. It uses testosterone through something called androgen receptors, which are essentially docking stations on prostate cells that testosterone binds to before it can trigger any cellular activity. The number of these docking stations is finite, and once they are all occupied, adding more testosterone to the system produces no additional effect on the prostate. The receptors are saturated.
Research published by Morgentaler and Traish in 2009 put a number to where that saturation happens: somewhere around 240 to 250 nanograms per deciliter of testosterone in the blood. Above that level, the prostate essentially stops responding to changes in testosterone. Below it, the relationship is steep and direct, meaning small changes in testosterone produce large changes in prostate activity. But most healthy men, and certainly most men on TRT, are operating well above 250 ng/dL. Which means the prostate is already fully saturated before any injection or gel enters the picture.
This is what makes the 1941 experiment so misleading as a framework for modern TRT. Huggins was working with castrated men whose testosterone had been driven down to near zero, which placed them far below the saturation threshold. In that range, adding testosterone back had a dramatic effect on the prostate because the receptors were empty and ready to respond. That is a very different situation from a hypogonadal man with a baseline of 200 ng/dL being brought up to 600. Both men got testosterone, but the biology of what happened to their prostates is completely different.
The saturation model makes a specific prediction: once you are above that 250 threshold, testosterone replacement should have little to no effect on prostate tissue, and therefore no meaningful effect on cancer risk. That prediction has now been tested in some very large populations.
The largest randomized trial on this question followed 5,204 men for an average of 33 months and measured prostate cancer rates directly. The result was 0.46 percent in the TRT group versus 0.42 percent in the placebo group, a difference that was statistically indistinguishable from chance, with a hazard ratio of 1.07 and a p-value of 0.87. A Finnish population study that followed 78,615 men over 18 years found not just no increase in prostate cancer mortality among TRT users, but actually a lower rate, with a hazard ratio of 0.52 compared to non-users. A meta-analysis pulling together 28 randomized controlled trials found that PSA, which is a marker of prostate activity, rose by an average of just 0.08 nanograms per milliliter in men on TRT, a number that is not clinically meaningful. Urinary symptoms, measured by the International Prostate Symptom Score, showed a change of exactly zero.
What these three datasets are showing, across very different study designs and populations, is the saturation model playing out in real life. When you start above the threshold, more testosterone does not move the needle on prostate outcomes.
The most direct test of the original fear, though, comes from a study that looked at men who already had prostate cancer. If testosterone drives cancer growth, then giving it to men who have already been treated for prostate cancer should cause their cancer to come back. A study of 69,984 men with treated prostate cancer found 1,012 who received TRT after their treatment. There was no increase in recurrence and no increase in death. If testosterone does not cause existing prostate cancer to recur, the mechanism required for it to initiate cancer in healthy tissue becomes very difficult to defend.
The practical takeaway from all of this is straightforward. TRT does not appear to cause prostate cancer, and the fear that it does traces directly back to a single experiment conducted on a population whose biology was fundamentally different from any man receiving TRT today. That experiment was not wrong in what it observed. It was wrong in what it concluded, and the conclusion has been carried forward for 80 years largely on the authority of the Nobel Prize attached to it.
If you are starting TRT, the monitoring approach endorsed by the Endocrine Society is to get a baseline PSA before you begin, check it again at three to six months, and then annually after that. If your PSA rises more than 1.4 ng/mL above your baseline, that warrants a conversation with a urologist, not because TRT caused a problem, but because that kind of movement deserves investigation regardless of why it happened.
The fear was not built on nothing. It was built on a real observation, interpreted through a model that did not account for receptor saturation, in a population that does not resemble TRT patients. Once you understand the saturation threshold, the 1941 data and the modern data stop contradicting each other and tell the same story.
The prostate does not care how much testosterone is in the blood once it has all the testosterone it can use.
References
- Huggins CV, Hodges CV. 1941. "Studies on Prostatic Cancer. I. The Effect of Castration, of Estrogen and of Androgen Injection on Serum Phosphatases in Metastatic Carcinoma of the Prostate." Cancer Research. 14:293-297. Finding: Castration reduced acid phosphatase in men with metastatic prostate cancer; testosterone injection into castrated men raised it back. Source
- Morgentaler A, Traish AM. 2009. "Shifting the paradigm of testosterone and prostate cancer: the saturation model and the limits of androgen-dependent growth." European Urology. 552:310-320. Finding: Prostate androgen receptors saturate at approximately 240-250 ng/dL; above this threshold, additional testosterone produces minimal prostate effect. Source
- Bhasin S, Travison TG, Pencina KM, et al. 2023. "Prostate Safety Events During Testosterone Replacement Therapy in Men With Hypogonadism: A Randomized Clinical Trial." JAMA Network Open. 612:e2348692. Finding: 5,204 men, 33 months. Prostate cancer: 0.46% TRT vs 0.42% placebo HR 1.07, p=0.87. No significant difference. Source
- Siltari A, Murtola TJ, Kausz J, et al. 2023. "Testosterone replacement therapy is not associated with increased prostate cancer incidence, prostate cancer-specific, or cardiovascular disease-specific mortality in Finnish men." Acta Oncologica. 6211-12:1755-1762. Finding: 78,615 men, 18-year follow-up. Prostate cancer-specific mortality LOWER in TRT users HR 0.52. Source
- Xu Z, Chen X, Zhou H, et al. 2024. "An updated systematic review and meta-analysis of the effects of testosterone replacement therapy on erectile function and prostate." Frontiers in Endocrinology. 15:1335146. Finding: 28 RCTs. PSA change: 0.08 ng/mL not significant. IPSS change: 0.00 literally zero difference. Source
- Sarkar RR, Patel SH, Parsons JK, et al. 2021. "Testosterone therapy does not increase the risks of prostate cancer recurrence or death after definitive treatment for localized disease." Prostate Cancer and Prostatic Diseases. 24:739-746. Finding: 69,984 men with treated prostate cancer, 1,012 received TRT. No increase in recurrence or death. Source
- Bhasin S, Brito JP, Cunningham GR, et al. 2018. "Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline." JCEM. 1035:1715-1744. Finding: Refer to urology if PSA rises >1.4 ng/mL above baseline. Source
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