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This was the title of a recent BMJ editorial. The general public and politicians do not understand screening. There is an inescapable logic in most peoples’ mind that suggests picking up a disease or cancer early is always a good idea. This unfortunately displays a naive belief in medical prowess for the following reasons.

Most tests are seriously flawed .There are false positives where the test is positive although the patient does not have the disease and false negatives where the patient has the disease but tests negative. The former leads to unnecessary, often dangerous painful further tests and treatment and the later provides false reassurance which may delay the patient seeking help when symptoms arise [this was why regular breast examination by health professionals was stopped].

The natural history of the disease is unknown. Many, early cancers never progress. They remain as ‘pussy cat’ cancers rather than ‘tigers’ living with their owner never harming them.  In the press this week it was reported that statistically 4 women will have had needless treatment  for breast cancer for every one woman who has had life saved by the breast screening programme.

The press also reported yesterday that a large Canadian study had concluded that prostate screening does more harm than good. Prostate cancer is so common that the majority of men over 50 have it and by the age of 90 post mortem examinations show that about 90% of men have cancerous cells in their prostate. In the vast majority this cancer will never do anything and cause no discomfort and the person will die of something else and never be aware of it. Treating prostate cancer by surgery can lead to erectile dysfunction and often incontinence. Alternative hormonal treatment for prostate cancer involves a ‘chemical castration’ blocking the effects of testosterone which the cancer thrives on. A lack of testosterone in men causes problems with libido, weight gain and depression.  We desperately need to be able to distinguish between the pussy cat cancers and the tigers which are killers. Until then mass screening and treating more men will do more harm than good.

David Cameron also announced  last week that GPs were going to be paid £55 for every dementia diagnosis to encourage dementia screening.As a GP I find it insulting that he thinks I would not do the best I could for my patients without being bribed.   Dementia is a notoriously hard diagnosis to make. There isn’t a simple reliable test, it is impossible to predict how a patient will be affected by it, there isn’t an effective treatment available particularly in the early stages and there is no evidence that early detection is useful. A host of other conditions including depression have an effect on short term memory. Imagine the harm to a depressed patient by suggesting that they may have dementia.

Experts recommended being more honest with the harm associated with screening. It is true that screening saves lives but it is also true that screening leads to unnecessary anguish, painful procedures and even death.

In medical ethics the benefit [beneficience] always has to be weighed against the harm [maleficience]. Screening should be left to experts such as the Chief Medical Officer to decide  on the basis of evidence not by politicians who do not have enough understanding and seek to score points against each other.