Prostate cancer: another chronic case of over-diagnosis?

Prostate cancer is the most common cancer in men, with 35,000 new cases a year and 10,000 deaths. It is also one of the most rapidly increasing cancers but there is no reliable test for the disease.

In the US, screening for prostate specific antigen (PSA) in the blood is widespread, even though it is unreliable, and there are demands for it to be introduced in the UK. But research published this month says it is responsible for an "epidemic of overtreatment".

As many as 60 per cent of prostate cancers detected with the PSA blood test are overdiagnosed. The next stage after a positive PSA test is a biopsy, a painful procedure in which a needle is inserted through the rectum into the prostate gland and a sample of tissue removed for examination to confirm the presence of cancer. But two out of three men with a raised PSA will not have any cancer cells in their prostate biopsy. Conversely, up to one in five men with prostate cancer will have a normal PSA result.

Even if cancer is diagnosed it is not necessarily life-threatening. Specialists distinguish two kinds of prostate cancers – the "tigers" which are virulent, aggressive and require radical surgery and radiotherapy; and the "pussy cats" which are indolent, slow-growing and may require no treatment beyond "watchful waiting" or regular monitoring.

The US research, published in Archives of Internal Medicine, found that men with prostate cancers detected in screening were significantly less likely to have high-risk disease but more likely to have invasive treatment. PSA has been around for two decades but remains a "poor test" for prostate cancer and it is time we came up with something better, the researchers say.

There is a risk of overdiagnosis and unnecessary treatment with all screening tests which has to be balanced against the benefit of detecting cancer early and treating it while there is the best chance of a cure. The NHS has screening programmes for cervical cancer and bowel cancer, where the evidence that the benefits outweigh the harm is much higher, but it has resisted pressure to screen for prostate cancer as the PSA test is too inaccurate.

Even successful screening programmes can have trouble justifying themselves when lobbying groups demand they be extended. Screening for bowel cancer has been proven as one of the most effective measures against the disease, which is the second biggest cause of cancer death in the UK.

It involves a simple test of the faeces for the presence of blood followed, if blood is present, by internal examination of the bowel and removal of polyps – small growths on the bowel wall – which cuts the incidence of the cancer by up to 50 per cent. The examination, diagnosis and treatment are carried out together in a single procedure and need never be repeated, minimising discomfort, anxiety and costs.

However, bowel cancer charities say the age for starting screening should be lowered from the present 60 to 50. Experts are resistant because 83 per cent of cases occur in the over-60s.

In the case of screening for cervical cancer, also established as a programme where the benefits outweigh the harm, demands for the starting age to be reduced from 25 to 20, after the reality TV star Jade Goody's death from the disease last year, have been rejected for the same reason that there are too few cases and too high a risk of overdiagnosis.

Screening undoubtedly helps some individuals but hurts others. No right answer to whether it is worthwhile exists. It is a personal choice.