Letters

Screening and mortality from cervical cancer

Does screening really reduce mortality?

Authors' reply

Study shows importance of centralised organisation in screening

Does screening really reduce mortality?

EDITORWe were rather non-plussed to read that the conclusion of the paper by Quinn et al on screening for cervical cancer¹ is not supported by their data, and we wonder whether so called political correctness had anything to do with it. The statement "800 deaths might have been prevented in 1997" is based on a projected mortality of a completely arbitrarily (alas, not randomly) selected part of a subset of graphs showing trends in mortality. The opposite conclusion may be reached using the same graphs. For example, in women aged 35-44 mortality fell from 10 per 100 000 to 5 per 100 000 in the period 1960 to 1975, and it should have approached zero by 1997 assuming that the trend had continued. Similarly, with the same age groups as in the original paper, in women aged 25-34 mortality fell from 2.5 per 100 000 to 1.1 per 100 000 in the period 1955 to 1965, so by 1997 it should have again approached zero. Since the only new intervention has been screening, and the mortality is excessive at 5 per 100 000, screening may have caused up to 2900 extra deaths in 1997by the same logic.

Jayant S Vaidya, honorary lecturer in surgery. 
j.vaidya@ucl.ac.uk

Michael Baum,  professor of surgery. 
Department of Surgery, Royal Free and University College Medical School, University College London, London W1P 7LD

Authors' reply

EDITORThe conclusions in our paper are not based solely on the analysis of mortality. We presented strong evidence that the introduction of national call and recall and of incentive payments to general practitioners led to a dramatic fall in the incidence of cervical cancer in women in all age groups from 30 to 74 and in all regions of England. Other evidence confirms the expected shift towards detection of earlier stages of disease. There is no other plausible explanation for these patterns. If women do not get cervical cancer, they will not die from it. In addition, it has been recognised for over 30 years that mortality from cervical cancer shows very strong cohort trends (reflecting those in incidence)¹ and so Vaidya and Baum's simple extrapolation of age specific trends is totally inappropriate. We extrapolated the cohort rates for the relevant age groups. Our analysis and conclusions are supported by a similar study in Scotland² and by the results from formal age period cohort models.³

We remain deeply concerned about the many well known problems with cervical screening which we mentioned in our paper: cervical cancer is a comparatively rare disease and its natural course is not well understood; the smear test has both low sensitivity and low specificity; many tests are technically unsatisfactory and the proportion of such tests varies widely across the country; the mix of three and five year screening intervals is inequitable; too many smear tests are opportunistic; and the programme costs four times as much as breast screening. Nevertheless, there is now conclusive evidence that cervical screening has markedly reduced both incidence and mortality.

M J Quinn,  director, National Cancer Registration Bureau. 
P J Babb,  senior cancer epidemiologist. 
J Jones,  cancer epidemiologist. 
Office for National Statistics, London SW1V 2QQ

Study shows importance of centralised organisation in screening

EDITORThe paper by Quinn et al reporting the effects of screening on incidence of and mortality from cervical cancer in England¹ highlighted the characteristics of successful programmes elsewhere ^{2 3} and showed that the national screening programme had been effective.

The situation in Hong Kong, where there is no systematic population based cervical screening programme, shows the importance of central organisation. Hong Kong is a generally affluent community with a better health profile than most developed countries. Infant mortality is low (4.6 per 1000 live births in 1995, compared with 6.2 in the United Kingdom), and life expectancy is high (81.5 years at birth for women, compared with 79.4 years in the United Kingdom). Women in Hong Kong are at lower risk of developing many common cancers, such as those of the breast and lung, than are their counterparts in most Western countries yet the reverse is true for cervical cancer.⁴

The figure shows the trend in the incidence of and mortality from cervical cancer standardised to the European standard population (for age bands of five years). Although incidence has reduced gradually over time, it has not fallen dramatically as in the United Kingdom after organised screening achieved a coverage greater than 70%, and the death rate has changed little. The standardised incidence of 16.9 per 100 000 for invasive cancer in 1994 was higher than the baseline rates of disease before organised screening started in the United Kingdom. Cervical cancer is the fourth most common newly diagnosed cancer and accounts for 4% of deaths from cancer in local women, compared with 2% in the United Kingdom.

One of us (PA) recently found that 56% of nearly 1800 women aged between 20 and 75 in Hong Kong had never had a cervical screening test.⁵ Coverage was lowest among older women (72% of women over 50 had never been screened) and those in the lower socioeconomic groups. Less than a quarter of all women were screened regularly, and these were generally screened yearly or more often.

View larger version (18K): [in this window] [in a new window]   Age standardised incidence of invasive cervical cancer and mortality from cervical cancer, Hong Kong, 1982-7

The current screening system in Hong Kong is therefore inequitable, wastes resources, and results in avoidable cases of cervical cancer. It may also cause unnecessary harm by overscreening women at lower risk. The study by Quinn et al provides further support for centralised organisation in any screening system and is a message that should not be ignored by any country with a developed health care system.

Peymané Adab,  clinical lecturer. 
Sarah McGhee,  assistant professor. 
Anthony Hedley,  professor. 
Department of Community Medicine, University of Hong Kong, Patrick Manson Building South Wing, 7 Sassoon Road, Pokfulam, Hong Kong