A third of prostate cancers detected in older men using the standard PSA screening test would not cause actual symptoms during the patients鈥� lifetimes, according to a new US analysis. But the majority of these men undergo treatments that do have substantial side-effects.
鈥淭hese are people that would never know they had cancer without the positive screening result,鈥� says Grace Lu-Yao at the Cancer Institute of New Jersey, who has examined the findings. 鈥淏ut the most common treatments when the cancer is still localised are surgery or radiation, which do not have trivial side effects.
鈥淎 lot of people think there is no harm to having more cancer screening 鈥� but there are downsides. For older men, prostate screening may not be the best thing for them,鈥� she says.
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A team led by Ruth Etzioni at the Fred Hutchinson Cancer Research Center in Seattle, US, estimated prostate cancer 鈥渙ver-diagnosis鈥� between 1988, just after the test was widely adopted, and 1998.
The scientists created a computer model based on previous data to predict the number of cases that would have been detected during the lifetimes of two million men in the absence of the test. And they compared this figure with actual data from a US national cancer registry.
Aggressive cancers
About 29 per cent of diagnoses based on PSA test results in white men aged between 60 and 84 in 1988 were 鈥渙ver-diagnoses鈥�, they concluded. For African-Americans, the figure was 44 per cent. The average age of prostate cancer diagnosis is 72.
The PSA test detects levels of prostate-specific antigen. Higher levels are a good indicator of prostate cancer. But there is currently no way of knowing which men with positive PSA results will develop aggressive life-threatening cancers, says Lu-Yao, so most patients receive treatment.
鈥淚t would be best if we could develop a test to show which cancer is going to kill the patient and which will not,鈥� she says. 鈥淏ut unfortunately, the technology is not at that point yet.鈥�
Older men are particularly at risk of an over-diagnosis 鈥� simply because they may die of other causes before their prostate cancer develops to create noticeable symptoms.
鈥淪ome of these men will not benefit from knowing they have cancer,鈥� says Lu-Yao. 鈥淧atients should take the test if they want to 鈥� but they should understand what it means to have a positive test result, and to understand the risk of overdiagnosis.鈥�
Journal reference: Journal of the National Cancer Institute (vol 94, p 981)