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Why young women should be screened for cervical cancer: The distinction between CIN2 and CIN3

Dear Editor, We write in response to Sasieni et al. who refer to our article on the benefit of screening young women. We accept that their calculations (based on modeling) may be more or less correct in saying that ‘‘only’’ 3% of CIN3 would become invasive by age 25 years. During 2003, before implementing the policy of not inviting women aged 20–24 years for screening, 4,000 cases of CIN3 were registered in England in that age band. Those 120 women [3%] might disagree that screening was unnecessary. Furthermore, not all women are screened as soon as they reach age 25 years. Treating highgrade CIN is essentially a treatment of risk and reduces the likelihood of invasive cancer developing in subsequent years of life—after an unknown interval for any individual woman. We quoted the evidence of Peto et al. that at least 50% of CIN3 would eventually become invasive later in life. Highgrade CIN has always been detected and in most cases treated primarily in women aged 20–39 years. We accept that some may regress and that regression is probably more likely in younger women. But we see no clear evidence that management of CIN3 in women aged 20–24 should be any different from in those aged 25–34 years. In England as a whole, following the increased incidence in young women that led to the launch of the NHS Cervical Screening Programme in 1988, there was no decline during the following decade of incidence in women aged 20–24 years—but there was a decline both in women aged 25–29 and 30–34 years. In both those age bands it is beginning to rise again (Fig. 1). Furthermore, a 12-year audit of 382 cancers in Southampton and south west Hampshire showed a significant shift between 1985–87 and 1994–96 from highstage symptomatic cancers to screen-detected 1A and 1B cancers in women aged 20–34 years. In our view, screening young women has several purposes: i) to reduce the risk of invasive cancer by detecting and treating high-grade CIN when it is small enough in volume to be treated effectively, ii) to detect microinvasive and early cancers at a stage when treatment can often be offered without loss of fertility, iii) to monitor low-grade lesions so that highgrade CIN can be treated if it occurs during follow-up, and iv) to offer life-style advice (on diet, smoking cessation and use of condoms) to reduce the risk of low-grade lesions progressing to high-grade. The concern that this age group is more vulnerable to anxiety and may have unnecessary and potentially harmful treatment must be addressed not by excluding them from screening but by counseling and adherence to evidence-based protocols, especially for low-grade abnormalities. We see no evidence in the article by Sasieni et al. for the final clause (our italics) in the abstract ‘‘From this analysis, at most 1.5% of women treated (equivalent to 3% of CIN3 registrations) would have cancer by age 25 whereas it is reasonable to assume that over half of them would have regressed by age 25’’, which the authors misquote from their discussion: ‘‘This should be balanced against the likelihood that over half of the CIN2 and CIN3 treated at ages 20–24 would have regressed (without treatment) by age 25’’. We accept that 30–50% of CIN2 may regress, which was shown in the ALTS trial, but that did not apply to CIN3 (or HPV16þ CIN2) and is contrary to the evidence of molecular biological features of CIN3 as well as follow-up studies and reviews of false negative smears of women with cancer, which were referred to in our article. We believe that the final statement in the abstract, which we have already seen quoted out of context, is at best highly misleading.