ACCEPTING the latest recommendation on how to interpret a controversial test for prostate cancer would mean that more men will undergo unnecessary treatments that can leave them impotent or incontinent, say critics.
The test measures the level of prostate-specific antigen (PSA), an protein produced by the prostate gland. Prostate tumours pump out more PSA than normal. But ever since the test was first used 12 years ago, a battle has raged over whether the benefits justify the the risks, mirroring the debate over mammography screening for breast cancer in women.
Prostate tumours are the most common form of cancer in men. Nearly half of 50-year-old men, and 80 per cent of 80-year-olds, have some form of prostate cancer. But most tumours grow so slowly the men will die of old age before the cancer becomes dangerous. Only 3 per cent of men in the US die of the disease.
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Proponents of the test claim preliminary studies suggest that prostate cancer deaths in the US have decreased as a result of widespread PSA screening. But sceptics say that, until we can tell which tumours pose a serious threat, PSA testing merely encourages unnecessary and possibly harmful treatments.
Currently, if the concentration of antibodies in the blood is over 4.1 nanograms per millilitre, doctors recommend an invasive biopsy. If the biopsy is positive, doctor and patient decide whether the tumour is severe enough to require treatment 鈥� usually surgery or radiation therapy.
But a study published last week in The New England Journal of Medicine (vol 349, p 335) claims that the current threshold for antibody concentration means that only 18 per cent of cancers are detected in men under 60. Lowering the threshold to 2.6 nanograms per millilitre would increase the detection rate to 64 per cent.
鈥淭he PSA test simply works much better with a cut-off of 2.6 than with the current cut-off of 4.1,鈥� says team member William Catalona of Northwestern University in Illinois, who was the first to suggest using the PSA test to screen for prostate cancer. Martin Resnick, president of the American Urological Association, agrees: 鈥淚 am going to start talking to patients who fall at this new threshold.鈥�
But lowering the threshold would be irresponsible, says Mark Litwin of the University of California, Los Angeles. According to the US Preventive Services Task Force, surgery leaves between 20 and 70 per cent of patients impotent and between 15 and 50 per cent incontinent. 鈥淲ith prostate cancer, one doesn鈥檛 necessarily want to diagnose more cancer, one wants to diagnose more dangerous cancers,鈥� he says.
At the moment the only way to tell whether a tumour will take five or fifty years to become dangerous is to analyse the tiny slice of the prostate provided by a biopsy. This is not representative of the whole tumour, however, so the test regularly gets it wrong.