Screening interval and risk of invasive squamous cell cervical cancer

Abstract

Objective To compare the risks of developing invasive squamous cell cervical cancer associated with screening intervals of 1, 2, and 3 years after a negative cervical smear. Methods We conducted a matched case-control study of invasive squamous cell cervical cancer patients ( n = 482) diagnosed between 1983 and 1995 among long-term members of a large health maintenance organization. Controls were matched for age, length of membership, and race ( n = 934). Screening interval was time between the last negative cervical smear and the case diagnosis date. The main outcome measure was the relative odds of invasive disease associated with 1-year, 2-year, and 3-year intervals. Results The odds ratio for a 2-year versus a 1-year interval was 1.72 (95% confidence interval 1.12, 2.64, P = .013) and for a 3-year versus a 1-year interval was 2.06 (95% confidence interval 1.21, 3.50, P = .007). The odds ratio for a 3-year versus a 2-year interval was 1.20 (95% confidence interval 0.65, 2.21, P = .561). Controlling for ever having had an abnormal cervical smear or a previous consecutive negative smear did not substantially change these results. Conclusion In this large health plan, the relative risks of invasive squamous cell cervical cancer were significantly greater for 2-year and 3-year cervical cancer screening intervals compared with a 1-year interval, but not for a 3-year interval compared with a 2-year interval. Our findings need to be placed in the context of the low absolute risks of developing invasive cervical cancer during the first 3 years after a negative cervical smear before making policy recommendation.