A Problem with Screening?

27 Aug 2009

“Cancer screening programs are about mass populations, but we make decisions as individuals”.

The implications of this statement for policy and for public understanding of cancer screening were discussed in a workshop on attitudes to and beliefs about cancer held at the World Conference of Science Journalists in London in June, and ably led by Anna Wagstaffe and Peter McIntyre of Cancer World magazine. Cancer World, published by the European School of Oncology, examines cancer care from a multi-disciplinary perspective. The aim of this discussion was to explore ways of providing policy-makers and individuals with the information needed to make choices about – respectively – which groups to invite for screening, and when, or even whether, to accept invitations to be screened. Attending screening sessions can be inconvenient, and the tests themselves may be uncomfortable and even painful. Take-up rates will therefore only be high if the people called for screening believe, individually, that the tests are accurate and that they, personally, are at risk of the condition being screened for.

The website gives NHS guidelines for cancer screening in the UK. It currently covers four tumour types: cancers of the breast, cervical, bowel and prostate. The programme of cervical screening is the longest established and probably the best known; it came into particular prominence early in 2009 with the widely-reported death from this disease of “reality TV” star Jade Goody. The so-called “Goody effect” resulted in a welcome increase in cervical screening take-up amongst young, poorly-educated women: the group that is known to be at greatest risk of this disease. However, the same issue sparked a demand for the lowering of the age at which cervical screening is started from 25 to 20. In June, the independent Advisory Committee on Cervical Screening confirmed that they had found no new scientific reasons to change the original guidelines. Very young women often have benign and reversible changes in cervical cells that are treated “just in case”, and this treatment can lead to complications later in life.

Similar attitudes affect public perception of the programme of breast screening by mammography, which is currently offered to women between the ages of 50 and 70 in the UK, although older women may request screening. Surveys have shown that women tend to over-estimate their risk of contracting breast cancer, and under-estimate the age at which it is most prevalent. Other European countries – including, for example, Poland – start their mammography programmes at somewhat younger ages, and there is pressure in the UK to include younger women. Yet mammography can give inaccurate results, particularly in those younger (including early middle-aged) women with denser breasts. A Cochrane Review has shown that breast screening does not reduce mortality with statistical significance ; lives have been saved, but many more low risk pre-cancers and non-cancerous abnormalities have been treated, perhaps un-necessarily. Mammography may be of greatest value for women over 70, who are at greatest risk of developing breast cancer, but they are not routinely called for screening and there is no significant public pressure to include them.

Bowel cancer screening, using self-administered faecal occult blood tests, should now be offered to people between 60 and 69 in the UK. This test has been more widely available, and for longer, in other countries including the US. In the case of prostate cancer, however, differences between these two countries are very much more marked. Although prostate cancer is discussed on the NHS screening site, there is no organised screening programme in the UK. The recommended procedure is one of offering “informed choice”: the test for early prostate cancer, which involves a blood test for prostate specific antigen (PSA) levels, is offered only to men who request it. In contrast, this is routinely used as a screening test in many parts of the US.

The role and value of prostate cancer screening is controversial even in that country. It is often quoted that “more people die with prostate cancer than of it”; the PSA test, like all screens, is not 100% precise, and it cannot be used to distinguish between slow-growing tumours that often require no treatment and the minority that are aggressive and require immediate, often invasive intervention. A recent editorial in the New England Journal of Medicine highlighted reports of two large clinical trials, one reporting no mortality benefit and the other a relative 20% reduction in cancer deaths from broadly similar prostate screening programmes (Barry, M.J. (2009). NEJM 360, 1351-1354).

Maybe no test will ever be entirely precise. Missed cancers, and “false positive” results leading to un-necessary and often unpleasant treatment, will very likely always be present, so cancer screening may be of more benefit to the cancer community – with better knowledge of cancer prevalence influencing priorities for research and the distribution of resources – than for individuals. People need a greater understanding of both cancer and risk if they are to make the most appropriate decisions for themselves. Investing in the public understanding of cancer through projects such as the Framework 7 programme Eurocancercoms , launched in July with ecancer as one of the lead partners, can only help.