PCPT: What the Prostate Cancer Trial Found

A drug given to men who did not have cancer

Prevention trials are a different animal from treatment trials. Everyone taking part is well. Any side effect is a pure cost, paid by healthy people, against a benefit that may never arrive.

The Prostate Cancer Prevention Trial gave 18,882 men a daily tablet for seven years and then looked for cancer. Finasteride blocks the conversion of testosterone into dihydrotestosterone, the main androgen inside the prostate, so the reasoning was straightforward: less of that hormone might mean less cancer.

Who was enrolled, and how cancer was looked for

Field	Detail
Trial	Prostate Cancer Prevention Trial (PCPT)
Identifier	No ClinicalTrials.gov number is given in the published report
Design	Randomised prevention trial
Participants	Men aged 55 or older, normal digital rectal exam, PSA of 3.0 ng/mL or lower
Comparator	Finasteride 5 mg a day against placebo, for seven years
Primary endpoint	How many men had prostate cancer during the seven years

That is the trial's design, not advice. Whether finasteride suits you, and at what amount, is for your own doctor to judge.

Biopsy was recommended if the annual PSA — adjusted for the fact that finasteride lowers PSA — went above 4.0 ng/mL, or if the rectal exam became abnormal. The designers expected about 60% of participants either to be diagnosed during the study or to have a biopsy at the end of it.

That biopsy rule matters more than anything else in the trial. It is how cancer got found, and it did not work identically in the two groups.

Fewer cancers found

Prostate cancer was detected in 803 of the 4,368 finasteride men with final data (18.4%) and in 1,147 of the 4,692 placebo men (24.4%).

That is a 24.8% relative reduction in prevalence over the seven years (95% CI 18.6% to 30.6%, p<0.001), or about six fewer diagnoses per hundred men.

The high-grade signal

The cancers found in the finasteride group looked worse under the microscope.

Tumours graded Gleason 7 to 10 made up 280 of 757 finasteride tumours (37.0%) and 237 of 1,068 placebo tumours (22.2%), p<0.001. Counted across all the men rather than all the tumours, that is 6.4% of the finasteride group and 5.1% of the placebo group, p=0.005.

There are two ways to read that. One is that the drug pushes remaining cancers toward a more aggressive form. The other is that the two groups were not examined in the same way. Finasteride shrinks the prostate and lowers PSA, so the biopsy trigger and the sampling of the gland worked differently in the two arms. The trial as designed cannot separate those explanations.

Eighteen years later, survival was identical

A follow-up published in 2013 tracked the participants for up to 18 years.

Across all 18,880 eligible men, prostate cancer was diagnosed in 989 of 9,423 on finasteride (10.5%) and 1,412 of 9,457 on placebo (14.9%), a relative risk of 0.70 (95% CI 0.65 to 0.76, p<0.001). High-grade cancer was found in 333 (3.5%) against 286 (3.0%), relative risk 1.17 (95% CI 1.00 to 1.37, p=0.05).

Survival at 15 years was 78.0% with finasteride and 78.2% with placebo. The hazard ratio for death was 1.02 (95% CI 0.97 to 1.08, p=0.46). Among men who did develop prostate cancer, ten-year survival was also similar in both groups.

So neither the benefit nor the alarm translated into people living longer or shorter.

What to keep in perspective

• The endpoint was diagnoses, not deaths. The trial was never designed to show whether men live longer, and the long follow-up says they did not.
• Detection differed between the arms, which makes the high-grade finding genuinely ambiguous rather than simply reassuring or simply alarming.
• Sexual side effects were more commonly reported with finasteride; urinary symptoms were more commonly reported with placebo. Those are real costs and benefits paid by well men.
• Everyone here started with a normal exam and a PSA of 3.0 or below. Results do not carry over to men outside that description.

Questions about prostate cancer prevention

• Am I in the group this trial studied, and what is my current PSA?
• If a drug lowers the number of cancers found but not the number of deaths, what is it buying me?
• What would you monitor if I took something like this for years?

Sources

This article was written from the sources below, which were checked on the source-check date shown above.

• NEJM: The Influence of Finasteride on the Development of Prostate Cancer (PCPT) (primary)
• NEJM: Long-Term Survival of Participants in the Prostate Cancer Prevention Trial (primary)

How this article was prepared

Prepared by Cancer Explained's AI-assisted editorial system and checked against the sources listed below. This article has not been reviewed by a healthcare professional unless a named reviewer is specifically shown.

Cancer Explained is published by the National Cancer Information Foundation as a nonprofit-oriented public-interest education project. It is not a diagnostic service, does not recommend treatments, and is not for emergencies.

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