Invasive cervical cancer audit: why cancers developed in a high-risk population with an organised screening programme.

Objectives: To investigate why invasive cervical cancers developed in a high-risk urban population with an established screening programme and to place cancers in the context of high-grade cervical intraepithelial neoplasia (CIN) and cervical glandular intraepithelial neoplasia (CGIN) diagnosed during the same period of time.
Study Design: Observational study of CIN2+ (CGIN, CIN3 and CIN2) and invasive cervical cancer diagnosed at Guy's and St Thomas' NHS Foundation Trust in 1999-01, 2002-04 and 2005-07 and audit of screening histories of women with invasive cancer analysed according to route to diagnosis, histological type and International Federation of Obstetrics and Gynecology (FIGO) stage.
Results: There were 133 invasive cancers, 53 CGIN, 1502 CIN3 and 1472 CIN2. Screen-detected cancers in asymptomatic women comprised 48.9% of cancers and were successively more likely to be in younger age groups (P = 0.03); all except one were stage IA or IB1. Screen-detected IA cancers were more likely (P < 0.001) to be in women screened within 0.5-5.0 years (80.5%) than screen-detected fully invasive (58.3%) or symptomatic cancers (35.3%). Seventy-one (53.4%) women had been screened within 0.5-5.0 years; 11 had negative cytology within 0.5-3.5 years and two tests within 10 years. The other 60 had negative tests less frequently or had previous abnormal cytology, colposcopy or treatment. Potentially avoidable factors were often multiple, including false-negative cytology, high-grade cytology reported as low-grade and lapses in attendance either for routine or repeat screening, or for colposcopy or treatment.
Conclusion: While often potentially avoidable, cancers in previously screened women tended to be early stage, detected by cytology and rare when compared with high-grade CIN.