Malagón T, et al. - Researchers intended to clarify recommendations of the best age at which to stop cervical cancer screening in developed countries. For this purpose, they estimated the remaining lifetime risk of cervical cancer at different ages and with different exit screening tests by using a Markov model of cervical cancer screening. As per observations, screening with cytology up to age 75 years might lead to reductions in cervical cancer risk, but with weakening returns. For unvaccinated women with a cervix after the age of 55 years, a correlation was observed between a negative exit oncogenic HPV test or negative HPV test plus cytology and a low remaining lifetime cervical cancer risk.

Methods

• Researchers created a state transition (Markov) model of cervical cancer natural history and screening for this modelling study.
• They used Canadian provincial registries and survey data to develop, calibrate, and validate the model.
• A new cohort of 236,564 women (one fifth of the population of Canadian women aged 20–24 years in 2012) entered the model every year and were successively modelled in parallel to simulate an age-structured population in the model.
• An age-structured population of women aged 10–100 years was created as successive cohorts entered the model at age 10 years.
• They excluded women who had a total hysterectomy.
• Using data from Statistics Canada, which compiles the data from 13 individual provincial registries, calibration of the model to human papillomavirus (HPV) infection and cancer incidence was done.
• The lesion severity-based disparities in management and treatment decisions were included by choosing a three-stage progressive cervical intraepithelial neoplasia model.
• They modelled infections with four high-risk HPV groups: HPV16 and HPV18; HPV31, HPV33, HPV45, HPV52, and HPV58; HPV35, HPV39, HPV51, HPV56, HPV59, HPV66, and HPV68; and a generic group of other potentially oncogenic HPVs.
• For older, unvaccinated women who stopped screening at different ages and underwent different screening tests, the 5-year, 10-year, and remaining lifetime risk of cervical cancer was determined.

Results

• In women aged 80–84 years, underestimation of the incidence of cervical cancer by up to 71% was seen in women with a cervix, excluding women with hysterectomies.
• According to prediction by the model developed in this study, a 1 in 45 (95% percentile interval 1 in 32 to 1 in 64) lifetime risk of cervical cancer has been documented for women without HPV vaccination who have been never screened.
• The lifetime risk of cervical cancer could be attenuated to 1 In 532 women (95% percentile interval 1 in 375 to 1 in 820) without HPV vaccination by perfect adherence (100% of women screened) to cytology screening every 3 years between the ages of 25 years and 69 years.
• Findings revealed incremental decreases in cancer risk later in life by increasing the age at which women stopped cytology screening from 55 years to 75 years.
• Screening cessation may lead to an average remaining lifetime risk of 1 in 588 (<1%; 95% percentile interval 1 in 451 to 1 in 873) in a 70-year old woman whose screening history was unknown.
• With regard to her remaining lifetime risk at age 70 years, reduction to 1 in 1,206 (2.0 times reduction; 95% percentile interval 1 in 942 to 1 in 1,748) was seen if she had a negative cytology test, 1 in 6,525 (12.9 times reduction; 95% percentile interval 1 in 3167 to 1 in 18,664) if she had a negative HPV test, and 1 in 9,550 (18.1 times reduction; 95% percentile interval 1 in 4928 to 1 in 23,228) if she had a negative co-test for cytology and HPV.