Harms and benefits of screening to prevent cervical cancer

Harms and benefits of screening to prevent cervical cancer

Harms and benefits of screening to prevent cervical cancer Julian Peto and colleagues (July 17, p 249)1 present an excellent review of trends in cervic...

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Harms and benefits of screening to prevent cervical cancer Julian Peto and colleagues (July 17, p 249)1 present an excellent review of trends in cervical cancer mortality, and warn about the high rates observed in British women. However, both their projection of a hypothetical cervical cancer epidemic without screening and their calculated costs per life saved are an unscientific exercise in screening advocacy. First, Peto and colleagues assume that “by 1978, about 40% of cervical cancers in women younger than 40 years were already being prevented”. The selective reference to a single paper from 19852 turns a weak hypothesis, based on a short time series of 15-year cancer incidence (1963–78), into a fact. The actual report presents a time series of mortality of 50 years (1953–2002); figure 2 suggests little change before 1988. This finding is confirmed by another article3 referenced by Peto and colleagues, sadly omitting the fact that screening had had no impact on mortality before 1988. To obtain a 40% incidence reduction, screening needs to be very effective, with a high coverage and a good quality of Papanicolaou (Pap) testing. Opportunistic screening overscreens women at low risk, misses women at high risk, and shows a high variability in the quality of Pap test. Second, Peto and co-workers assume that cervical cancer risk in the future is a constant, unchanging one. The cohort born in 1952 was aged 16 years in 1968, the beginning of the sexual revolution. The advent of AIDS changed sexual behaviour radically. Female gonorrhoea dropped from about 25 000 at the end of the 1970s to 4000 in 1995.4 Peto and colleagues refer to the recent doubling of gonorrhoea. It increased again to 6000, which is less than a quarter of what it was 25 years ago; half of these new cases arise in black ethnic groups.4 Third, Peto and colleagues ignore the considerable costs of overdiagnosis and www.thelancet.com Vol 364 October 23, 2004

overtreatment, which are part of cervical cancer screening.5 1% of the women might be saved, at the costs of overdiagnosing and overtreatment in 40%. While The Lancet attacks the pharmaceutical industry for only giving the good news and withholding the bad news, the bad news of cancer screening is rarely published. That the screening industry still withholds correct information on both the benefits and the harms of cancer screening, stated as number needed to treat (mortality averted) and number needed to harm (additional diagnostic and therapeutic interventions generated), is unacceptable. Peto and co-workers correctly point to a serious failure of public health in the past: a failure to maintain sexual hygiene. But, they further assume that public health remains ignorant and impotent. A-B-C campaigns (Abstain, Be faithful, use Condoms) are not only for Africans; residents of the UK did make good use of sensible sexual health promotion, witnessed by the steep decline of sexually transmitted diseases. A rational cervical cancer prevention programme would be ABCD, with the added D for Detect those at high risk. Such a programme would save resources, prevent anxiety and unnecessary treatment in many women, improve primary prevention of all sexually transmitted diseases, including AIDS, and improve detection, surveillance, and treatment of women who are truly at risk.

Luc Bonneux [email protected] Belgian Healthcare Knowledge Center (KCE), Residence Palace, 10de verdieping, Wetstraat 155, B-1040 Brussels, Belgium 1




Peto J, Gilham C, Fletcher O, Matthews FE. The cervical cancer epidemic that screening has prevented in the UK. Lancet 2004; 364: 249–56. Parkin DM, Nguyen-Dinh X, Day NE. The impact of screening on the incidence of cervical cancer in England and Wales. Br J Obstet Gynaecol 1985; 92: 150–57. Sasieni P, Adams J. Effect of screening on cervical cancer mortality in England and Wales: analysis of trends with an age period cohort model. BMJ 1999; 318: 1244–45. PHLS; DHSS & PS and the Scottish ISD(D)5 collaboration group. Sexually transmitted infections in the UK: new episodes seen at


genitourinary medicine clinics, 1991 to 2001. London: Public Health Laboratory Service, 2002. Raffle AE, Alden B, Quinn M, Babb PJ, Brett MT. Outcomes of screening to prevent cancer: analysis of cumulative incidence of cervical abnormality and modelling of cases and deaths prevented. BMJ 2003; 326: 901.

Julian Peto and colleagues1 dismiss the fact that before relaunch of cervical cancer screening as a quality assured national programme, for every death prevented, 57 000 tests had to be done and almost 2000 women had abnormal screening results.2 Their article takes us back to the days when effectiveness of screening was seen as a yes/no question, and anyone advocating a more sophisticated approach was attacked as a heretic.3 We believe that the lessons of the past are crucially important, and they are being ignored. Men need to be protected from the damage that the first 20 years of cervical screening inflicted on women;4 haphazard prostate screening, not backed by evidence, is already being delivered to 5–10% of men older than age 50 years and is resulting in considerable harm. We agree with Peto and colleagues that the cervical screening programme is successful, and will be more so in the future, but their estimates of future deaths prevented are probably somewhat high because of their 1·67 inflation factor based on an outdated report.5 Peto and colleagues confuse past, present, and future benefit, make simplistic estimates of cervical intraepithelial neoplasia (CIN) progression, cost per life saved, and numbers needed to screen, and omit the possibility of screening related harm. The age period cohort model used by Peto and colleagues is essentially the same as that used by us and by others.6,7 That they dismiss the results of our analysis of true-life screening records in a quarter of a million women during 1976–96 is, therefore, strange. Their estimates do not contradict ours, since they relate to a different period and to younger women, who might have a higher risk than the women in our cohort. Their estimate of CIN progression is not

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