Effectiveness of Cervical Testing in and outside a Screening Program—A Case-Control Study

SIMPLE SUMMARY: Opportunistic cervical testing is a common practice in many countries. However, quality control of tests outside national screening programs is often not possible. We conducted a case-control study on the effect of cervical testing in and outside the Finnish screening program on the risk of cervical cancer. Women undergoing cervical tests in five- or three-year intervals had a lower risk of cancer compared with those not tested. Testing was effective in and outside the screening program. However, program tests should be preferred for cost-effectiveness. Our results also strengthened the previous findings in the literature, that cervical screening is most effective in women aged 35 and over, and preventive effects can be seen until very old ages. ABSTRACT: In many countries with organized cervical cancer screening, opportunistic Pap and human papillomavirus (HPV) tests are common. However, little is known about their effectiveness. We examined the effect of testing in and outside the Finnish screening program on the risk of cervical cancer. We conducted a case-control study that involved 1677 cases with invasive cervical cancer that were diagnosed between 2010 and 2019. Five- and three-year test intervals were analyzed across all ages, by age group and by cancer morphology subtype. Conditional logistic regression was used, adjusting for socioeconomic variables. Women undergoing any kind of cervical test had a significantly lowered risk of cervical cancer (adjusted OR = 0.43, 95% CI = 0.38–0.48, tests in five-year intervals). The results were similar, regardless of whether the test had been taken in the screening program or outside of it, or whether the interval was five years or three years. Testing of women at ages 35–64 showed the strongest effects, but moderate preventive effects were seen until age 79. No significant effect was seen below age 30. Tests in and outside the program were effective at the screening target age. However, participation in the program should be encouraged for optimal cost-effectiveness. Preventive effects were also seen above the program target ages.