To prevent cervical cancer, many women are treated for cervical intraepithelial neoplasia (CIN) with excision of the lesion. Although this treatment is considered to be highly effective, 10-15% of treated women will have residual or recurrent disease.1 2 3 Accurate assessments of the risk of cervical cancer after such treatment can guide the development of the most effective post-treatment surveillance strategy. In a linked paper (doi:10.1136/bmj.e6855), Rebolj and colleagues found a fourfold greater risk of cervical cancer in women who completed their post-treatment follow-up compared with those with a normal primary smear.4

To judge the importance of these findings in relation to post-treatment surveillance strategies, it is important to understand what is being measured. Firstly, a substantial proportion of post-treatment cancers probably result from so called residual disease. In such cases the lesion was not completely excised and human papillomavirus (HPV) infection persists. If the residual lesion was small, it might take some time for it to regrow to a detectable size. Secondly, women treated for CIN whose lesion is completely excised may …