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Cervical cancer screening frequency
- Panos Maouris (7 February 1999)
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Results of mathematical modelling should always be interpreted with caution
- M E van den Akker-van Marie (7 April 1999)
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Presentation
- Julian Holloway (10 December 1999)
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Panos Maouris, Consultant in Obstetrics & Gynaecology George Town Hospital, Cayman Islands
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Dear Sir, Whilst in the UK it may be a legitimate exercise to try to compute a more cost efficient way of administering the Pap smear screening program by reducing the recommended upper age limit of women to be screened (Sharlaw- Jonson et al., 318:356-361, BMJ 6 Feb 1999), it must not be forgotten that for the majority of the countries of the world the problem is quite different, namely the complete absence of a comprehensive Pap smear screening program. In a large number of countries the screening if there is any is patchy and fails to cover a large enough proportion of the population at risk to have any real impact on the incidence of cancer of the cervix. Cayman Islands is a British Dependent Territory in the Caribbean with the highest per capita income in the whole of the Americas and an established Pap screening service for over 20 years. Yet despite this in a recent retrospective study (performed by myself and Drs. J. Gupta and G. Evans-Belfonte) the incidence of cervical cancer between the years of 1992 and 1997 was found to be amongst the highest in the world at 42.7 per 100,000 women aged over 20 years. Furthermore, there was a dramatic increase in the incidence from 19.2 during the first 3 years to 62.6 during the last 3 years of the study. Over half (58.6%) of the cases of cervical cancer were in women under the age of 40 years and 75.9% did not have a Pap smear within 5 years of the diagnosis. During this time there was a 33% increase in the number of Pap smears performed but only an estimated 35% of the women over 20 years of age were covered by a Pap smear every 3 years. It follows that what we need in the Cayman Islands is to increase the uptake of Pap smears. In the last year, in association with the Public Health Services, the Cancer Society and the Medical & Dental Society involving all public and private doctors, we have undertaken a national public awareness campaign utilizing all the media and incorporating a month long free Pap smear promotion. During this month alone we performed 37% of the previous year's total number of Pap smears targetting women who had not had a Pap smear in the previous 2 years ( a large proportion of whom had never had a Pap smear). We have also established national guidelines regarding the frequency of Pap smears which we have set at 2 years (in accordance with the Australian National guidelines which represent a convenient 'compromise' between and the British and American recommendations). We have decided to target all women over the age of 18 without specifying an upper age limit in our promotional material as we feel this may negate some of the beneficial effects of our campaign by confusing the public. We do recognise however that if a woman has had several consecutive normal Pap smears and has reached a certain age, her risk of developing cervical cancer may be so small as to make Pap screening not 'cost effective'. This does not however mean that it is not worthwhile. In a society like the Cayman Islands were the patient bears the cost of the Pap screening, provided the patient is fully informed about her individual age risk, she should be in a position to decide whether to stop having Pap smears after a certain age. Perhaps what the health authorities in the UK should be asking next is 'how many women in the UK would be willing to pay for the cost of continuing screening after a certain age?' (assuming that they are fully informed about their own risks). Yours sincerely, Dr. Panos Maouris, MRCOG, FRACOG. |
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M E van den Akker-van Marie, mathematician Department of Public Health, Erasmus University Rotterdam, The Netherlands
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Editor, Sherlaw-Johnson and colleagues(1) favourably evaluated policies for withdrawing women before the recommended age of 64 from the cervical cancer screening programmes, using a mathematical model. However, their results were obtained with specific and uncertain model assumptions which were insufficiently subjected to validation and sensitivity analysis. From the description of the model in cited earlier papers, it appears that most new cases of CIN originate from younger ages. The duration is assumed to be independent from age and very long on average (50 years for CIN 3) implying that most invasive cancers occuring over age 50 started as CIN before age 50, which could thus be detected by screening before age 50. Hence, this model is bound to predict only small increases in incidence when women are withdrawn from screening before the recommended age of 64. The sensitivity analysis only considers small adaptations of this basic assumption. Other models(2-4), calibrated on detailed analysis of screening data and cancer incidence data, resulted in much lower estimates for the mean duration of CIN. These models would predict less favourable effects of withdrawal policies. Concerning use of HPV testing, present data on HPV allow for widely different model quantifications, some of which are favourable for use in screening and some unfavourable(5). Given this uncertainty it is not yet possible to conclude about the impact of withdrawing women if their smear test and a simultaneous test for high risk types of human papillomavirus are negative. M.E. van den Akker-van Marle M. van Ballegooijen R. Boer G.J. van Oortmarssen J.D.F. Habbema Department of Public Health Erasmus University PO Box 1738 3000 DR Rotterdam The Netherlands phone: + 31 10 4087714 fax: + 31 10 4089449 1. Sherlaw-Johnson C, Gallivan S, Jenkins D. Withdrawing low risk women from cervical screening programmes: mathematical modelling study. BMJ 1999;318(7180):356-61. 2. Brookmeyer R, Day NE. Two-stage models for the analysis of cancer screening data. Biometrics 1987;43(3):657-69. 3. Gustafsson L, Adami HO. Natural history of cervical neoplasia: consistent results obtained by an identification technique. Br J Cancer 1989;60(1):132-41. 4. van Oortmarssen GJ, Habbema JD. Epidemiological evidence for age- dependent regression of pre-invasive cervical cancer. Br J Cancer 1991;64(3):559-65. 5. van Ballegooijen M, van den Akker-van Marle ME, Warmerdam PG, Meijer CJ, Walboomers JM, Habbema JD. Present evidence on the value of HPV testing for cervical cancer screening: a model-based exploration of the (cost-)effectiveness. Br J Cancer 1997;76(5):651-7. |
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Julian Holloway, Student University of Kent
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I am in my final year of study at the University of Kent in Canterbury. I am currently reading Soft Operational Research and in the process of researching the cervical screening programme in the UK for a management science project. I have found this article very useful and informative to my studies.I have been asked to give a presentation on this article for my Soft OR module. My mother Mrs.Juliet Ward one victim's of the Kent and Canterbury blunder. This is one of thhe reasons I have chosen this subject to research and hopefully help make some changes. My mother is delighted that people are trying to make a change to the current program for the furture. We have also set up a web site for awareness about cervical cancer.Anyone please feel free to visit at: www.juliet-trust.org Julian Holloway |
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