Nowadays in high-income countries, many women turning age 60 have been adequately screened in their 50s. A previous study found that women who were adequately screened with no abnormality at ages 51-60 do not gain a statistically significant benefit from the extended screening test at ages 61-65 in terms of reducing subsequent invasive cervical cancer. To understand the underlying reason, we performed a population-based cohort study to investigate the cumulative incidence of cervical cancer in situ (CIS) in women aged above 60 who have been adequately screened at age 50s, aiming to predict their likely potential of progressing to invasive cervical cancer.
Women born between 1919 and 1945 who live in Sweden and had cervical screening records available since age 51 were identified in the Total Population Register. Their screening histories between ages 51-65 were retrieved from the Swedish National Cervical Screening Registry. Women who had at least two separate Pap tests at ages 51-60 without any abnormal finding were included in the analysis. CIS and invasive cervical cancer from age 61 to 80 were retrieved from the National Cancer Register. We estimated the cumulative incidence of CIS up to age 80 among women screened at ages 61-65, and compared to the cumulative incidence of invasive cervical cancer up to age 80 among women unscreened at ages 61-65.
Among 332,746 women who were adequately screened in their 50s, 1.9‰ (95%CI: 1.6‰-2.2‰) of women screened at ages 61-65 were found to have CIS, and 1.6‰ (95%CI: 1.2‰-2.0‰) of women unscreened at ages 61-65 were found to have invasive cervical cancer up to age 80.
Women who were adequately screened in their 50s with no abnormality presented a low risk of CIS after age 60, but these precursors are very likely to progress to invasive cervical cancer since the cumulative incidence of invasive cancer among women unscreened at 61-65 is close to the cumulative incidence of CIS. Therefore, the low effectiveness of cervical screening at ages 61-65 among women being adequately screened previously may due to a low incidence of precursor lesion. However, CIS above age 60 may be risky enough to warrant careful follow-up and treatment. In the scenario that more and more women turning 60 have been adequately screened, screening all of them after age 60 with public resources may not gain satisfactory cost-benefit, given the low incidence of precursor lesions and statistically insignificant effectiveness on cancer reduction. Future studies can endeavor to identify residual risk factors for developing precursor lesions after age 60 despite being adequately screened in the past.