High-grade cervical abnormalities and screening intervals in New South Wales, Australia.

OBJECTIVES

This study aims to determine the association of two versus three year screening intervals with the likelihood of detection of a high-grade cervical abnormality and cervical cancer.

METHODS

Data were obtained from the New South Wales (NSW) Papanicolaou (Pap) Test Register (PTR) and NSW Central Cancer Registry (CCR). Subjects were human papillomavirus (HPV) unvaccinated women aged 20-69 years who had a minimum of two Pap tests with a negative result at their first recorded Pap test (n = 1,213,295). Logistic regression was used to determine the association between screening interval and the likelihood of: (1) a cytological prediction of high-grade abnormality, defined as cervical intraepithelial neoplasia (CIN) 2 or greater; (2) a histologically confirmed high-grade abnormality; (3) a cytological prediction of cervical cancer and (4) a confirmed diagnosis of cervical cancer, controlling for potential confounders of age and socioeconomic status (SES) of area of residence.

RESULTS

For each year increase in the screening interval, the odds of a histologically confirmed high-grade abnormality increased significantly in women aged 20-29 years (odds ratio [OR] 1.24, 95% confidence interval [CI] 1.20-1.28) and in women aged 30-49 years (OR 1.11, 95% CI 1.06-1.16), but not in women aged 50-69 years (OR 1.08, 95% CI 0.89-1.32). Similar results were observed for cytologically detected high-grade abnormalities. The screening interval was significantly and positively associated with a cytological prediction of cervical cancer (OR 1.40, 95% CI 1.28-1.54) and a confirmed cervical cancer diagnosis (OR 1.66, 95% CI 1.33-2.07) in women aged 20-69 years. Despite the higher risks, we estimate that if the screening interval were increased from two to three years, and the number of women participating in treatment screening was the same as for biennial screening in NSW, then 140 (95% CI 60-220) fewer high-grade cytology results would occur per year, and there would be around 19 (95% CI -50- 89) fewer high-grade cases confirmed by histology. As the 95% CI covers zero in the latter estimate, there is no significant difference in expected confirmed high-grade abnormalities between biennial and triennial screening if the same number of women are screened triennally as biennially. [corrected] Equivalently, 2.3 (95% CI 1.8-2.8) and 1.9 (95% CI 1.5-2.4) extra cases of high-grade cytology and histology, respectively, would be expected per 1000 women with initially negative cytology if the screening interval were extended from two to three years.

CONCLUSION

Increasing the cervical screening interval from two to three years would be expected to significantly increase the odds of detection of a high-grade abnormality for NSW women aged 20-49 years and cervical cancer for NSW women aged 20-69 years. Accordingly, our study provides evidence in support of retaining the recommended cervical screening interval at two years for HPV unvaccinated, well women.