Evaluating the impact of age on prostate cancer overdiagnosis using long-term follow-up from a randomised trial

This study utilizing long-term data from the CAP randomized trial demonstrates that prostate cancer overdiagnosis increases substantially with age due to competing mortality risks, suggesting that opportunistic screening policies should be re-evaluated for older men.

The Gist

The Big Picture: The "False Alarm" Problem

Imagine you have a very sensitive smoke detector in your house. It's so sensitive that it goes off not just when there's a fire, but also when you burn a piece of toast.

In the world of prostate cancer, the "smoke detector" is a blood test called PSA. The problem this study looks at is overdiagnosis. This happens when the test finds a tiny, slow-growing "spark" (cancer) that would never have grown big enough to hurt the man or kill him in his lifetime. Because the test found it, doctors treat it. But the treatment (surgery, radiation) can cause real problems like incontinence or erectile dysfunction. So, the man suffers side effects from a "fire" that never would have burned down his house.

The Study: A Long-Term Experiment

The researchers looked at data from a massive, long-term experiment called the CAP trial.

• The Setup: They invited nearly 190,000 men to get a one-time PSA test. Another group of men didn't get invited (the control group).
• The Wait: They followed these men for a very long time—about 15 years. This is crucial. Most studies stop after 5 or 8 years, which is like checking the smoke detector too soon. You need to wait a long time to see if the "smoke" was just toast or a real fire.

The Main Discovery: Age is the Deciding Factor

The study found that whether a man gets "overdiagnosed" depends almost entirely on how old he is when he takes the test.

Think of life as a race.

• Young Men (e.g., age 50): They have a long race ahead of them. If a slow-moving "spark" is found, there is a good chance it will eventually grow big enough to cause a problem before the man finishes the race (dies of old age or other causes). So, finding it early might actually help.
• Older Men (e.g., age 70 or 80): They are near the finish line. If a slow-moving "spark" is found, the man is very likely to finish the race (die of heart disease, an accident, or old age) before that spark ever turns into a dangerous fire.

The Numbers:

• If a 50-year-old is diagnosed, there is about a 16% chance the cancer would never have been found in his lifetime if he hadn't been tested.
• If a 70-year-old is diagnosed, that chance jumps to 32%.
• If an 80-year-old is diagnosed, the chance skyrockets to 58%.

In other words, for an 80-year-old, more than half the time, the test is finding a "ghost" cancer that would have stayed hidden forever.

Why This Matters for Policy

The paper argues that many countries, including the UK, currently have a "loose" policy where men can just walk into a doctor's office and ask for a PSA test whenever they want (called opportunistic testing).

Because of this, many older men are getting tested. The study suggests this is a mistake.

• The Analogy: It's like checking the expiration date on milk in a fridge that is about to be thrown out. If you are 80, checking for a slow-growing cancer is like checking the milk date when you only have a few days left to drink it. You might find a problem, but you won't have enough time left to use the milk anyway.
• The Result: Older men are getting treated for cancers they didn't need to know about, leading to unnecessary suffering and lower quality of life.

What the Paper Does NOT Say

• It does not say we should stop testing young men. In fact, it suggests the risk of overdiagnosis is much lower for them.
• It does not say we should ban all testing. It suggests we need to be smarter about who gets tested and when.
• It does not claim that the test is useless. It just says the "cost" of finding a cancer (the side effects of treatment) often outweighs the "benefit" (saving a life) for older men because they are likely to die of something else first.

The Bottom Line

This study uses a 15-year "time machine" to show that age is the most important factor in prostate cancer overdiagnosis.

• Younger men: The test is more likely to find a real threat that needs attention.
• Older men: The test is very likely to find a "harmless ghost" that leads to unnecessary treatment.

The authors suggest that doctors and policymakers need to rethink the rules so that older men aren't subjected to tests that cause more harm than good.

Technical Summary

Technical Summary: Evaluating the Impact of Age on Prostate Cancer Overdiagnosis

Problem Statement
Prostate cancer overdiagnosis—the detection of cancer via PSA testing that would not have been clinically diagnosed within a patient's lifetime—remains a primary concern for policymakers due to its negative impact on quality of life (e.g., incontinence, erectile dysfunction, anxiety). While extended follow-up from randomized trials has clarified that PSA screening reduces mortality, uncertainty persists regarding whether these benefits outweigh the harms of overdiagnosis. Current estimates often rely on complex microsimulation models with untestable assumptions or short follow-up periods that fail to capture the full "compensatory drop" in cancer incidence. Furthermore, the specific impact of age on overdiagnosis, driven by competing mortality risks, requires empirical evaluation using long-term data.

Methodology
The authors utilized long-term follow-up data from the CAP (Cluster Randomized Trial of PSA Testing for Prostate Cancer), a mature randomized trial with a one-off (stop-screen) design.

• Data Source: The study analyzed 189,386 men invited for a one-off PSA screen (intervention) and 291,445 men in the control arm. Follow-up data on vital status and cancer registration were collected through December 21, 2020, providing a median follow-up of 15 years.
• Overdiagnosis Estimation: The authors employed a competing risks framework to estimate overdiagnosis ($O(t)$). They first calculated the "net excess" incidence ($E(t)$) by comparing the cumulative incidence of prostate cancer in the screening arm ($F_A(t)$) versus the control arm ($F_B(t)$), adjusted for the baseline screen detection rate ($R_A = 1.19\%$).
  • Formula: $E(t) = \min[1, \{F_A(t) - F_B(t)\}/R_A]$.
• Competing Mortality Adjustment: To project overdiagnosis by age, the authors combined the net excess estimates with English male all-cause mortality rates (2021-23), subtracting age-specific prostate cancer mortality. They assumed net excess is independent of competing mortality and age.
• Projection: Using standard competing-risks methodology, they projected the probability that a screen-detected cancer would not have been diagnosed within 15 years due to death from other causes, stratified by age at diagnosis (50 to 80 years).

Key Results

• Net Excess Incidence: At 15 years, the cumulative incidence of prostate cancer was 7.08% in the screening arm versus 6.94% in the control arm. This yielded an absolute net excess difference of 0.14% (95% CI: -0.04% to 0.37%).
• Net Overdiagnosis: Relative to the 1.19% of men who had cancer detected at the initial screen, the net excess incidence at 15 years represented 11.7% (95% CI: 0.0% to 26.7%) of screen-detected cases.
• Impact of Age: Overdiagnosis risk rises substantially with age due to competing mortality:
  • Age 50: 16% chance the cancer would not have been diagnosed within 15 years without screening.
  • Age 70: 32% chance.
  • Age 80: 58% chance.
• Follow-up Maturity: The data suggests the "compensatory drop" in incidence (where screening arm incidence falls below control arm incidence as early diagnoses are exhausted) may not have fully concluded at 15 years, as the excess incidence continues to decrease.

Significance and Claims
The paper claims that age is the main driver of overdiagnosis in PSA screening. By utilizing a 15-year follow-up from a unique one-off screening trial, the authors provide empirical evidence that overdiagnosis is relatively low for younger men (e.g., aged 50–64) but becomes substantial for men over 70.

The authors argue that these findings challenge current opportunistic testing policies in the UK and other high-income countries, which have led to high screening rates in older men (70+). They posit that screening older men is unlikely to confer mortality benefits due to high competing mortality rates, while simultaneously exposing this demographic to high risks of overdiagnosis and subsequent unnecessary treatment.

The study also critiques existing microsimulation models used by the UK National Screening Committee, suggesting they may substantially overestimate overdiagnosis for younger men (e.g., projecting 28% for age 50 vs. the study's lower empirical estimates) and fail to account for the potential of organized screening to reduce overdiagnosis compared to opportunistic testing. The authors conclude that policy re-examination is necessary to align screening practices with the age-dependent risks of overdiagnosis.