Long-term risk of invasive cervical cancer after treatment of squamous cervical intraepithelial neoplasia.

Invasive cancer of the cervix after treatment for cervical intraepithelial neoplasia (CIN) is becoming more important, as screening reduces the incidence of invasive disease. The rate of invasive cervical or vaginal cancer following treatment for CIN in UK remains elevated for at least 8 years. The aim of our study was to determine from international data how long this rate remains elevated and whether the rate of invasive disease reflects the rate of posttreatment CIN. The aim was to determine why the rate of invasive disease does not fall. A search of Medline and a secondary search of cited references identified 1,848 articles referring to the success rate of the treatment of CIN. Only 26 cohorts from 25 articles met all the inclusion criteria. The policy in these was to perform at least annual smears. After the first year following treatment for CIN, the rate of invasive disease remained about 56 per 100,000 woman years until at least 20 years after treatment. This rate is approximately 2.8 times greater than expected. In contrast, the risk of posttreatment CIN declined steadily with time to about 190 per 100,000 women in the 10th year. Although the posttreatment rate of CIN falls with time, the rate of invasive disease remains static. It seems likely that this is due to diminishing compliance with follow-up. Women should be encouraged to persevere with annual smears for at least 10 years after their treatment as this may offer them the best chance of detecting recurrence at a treatable stage.