Cervical screening

Abstract

With respect to your editorial1Lancet. 1999; 354 (Editorial.): 1833Summary Full Text Full Text PDF PubMed Scopus (6) Google Scholar about the judgment on the Kent and Canterbury appeal, the dust needs to settle before we can assess the extent of the damage caused to the screening programme by that whole debacle. You also make some comments without references that could be misleading. Women are therefore placed in double jeopardy by the idea on one hand that screening may be unnecessary and on the other that it is rather ineffective. Neither is true. The rate of cervical cancer may have been falling when screening was first introduced in the 1960s, but the risk has increased for women born since about 1940. In the 1980s it was recognised that disorganised screening was failing to control an increased rate of invasive cervical cancer in young women, who may have been at maximum risk of disease now if screening had not improved.2Draper GJ Cook GA Changing patterns of cervical cancer rates.BMJ. 1986; 287: 510-512Crossref Scopus (69) Google Scholar Before the introduction of screening, the peak incidence of cervical cancer in England was in women in their late 40s.3Gustafsson L Ponten J Bergstrom R Adami H-O International incidence rates of invasive cervical cancer before cytological screening.Int J Cancer. 1997; 71: 159-165Crossref PubMed Scopus (165) Google Scholar Resources were put into improving coverage and quality control, as a result of which incidence has fallen by 42% between 1990 and 1996.4Herbert A Bryant TN Campbell MJ Smith J Investigation of the effect of occult invasive cancer on progress towards successful cervical screening.J Med Screen. 1998; 5: 92-98Crossref PubMed Scopus (10) Google Scholar The fall is more impressive when set against a predicted rise. An individual cervical smear test may have an overall sensitivity as low as 70%, for reasons of sampling more than accuracy of screening. However, regular screening achieves a high level of sensitivity and was the only method of detecting the consistent 18 000 or so cases of cervical intraepithelial neoplasia grade 3 (CIN3) that have been registered each year since 1988 by the Office for National Statistics (http://www.ons.gov.uk assessed Dec 30, 1999). A similar number of cases of CIN2 have been treated each year, and detected in the same way, but the cases are not registered nationally. How much more high-grade CIN is there to be found? Now that invasive cervical cancer is an uncommon disease, affecting nine women per 100 000, it is likely that only a third of those cancers are clinical cases arising in previously screened women. A study in Southampton showed a shift from high-stage symptomatic cancers to occult screen-detected cancers as the overall rate fell.4Herbert A Bryant TN Campbell MJ Smith J Investigation of the effect of occult invasive cancer on progress towards successful cervical screening.J Med Screen. 1998; 5: 92-98Crossref PubMed Scopus (10) Google Scholar In 1994–96 in Southampton, when the rate was the same as in England and Wales, 40% of cancers were occult screen-detected cancers and half of these were stage IA cancers with prognosis and treatment similar to CIN3. 35% of cancers were in women who had never been screened (unpublished personal observations). If those percentages are similar in the country as a whole, there are now only about 600 clinical cancers each year in previously screened women. There are many reasons for screening not preventing cervical cancer, of which misreading a smear is only one. Cervical screening was not introduced as a costsaving measure. However, the increased costs and availability of chemotherapy mean that we might have needed the £132 million spent each year on screening if all highgrade CIN had remained undetected.