Screening for cervical cancer - an evidence-based approach

Introduction: The Papanicolau (Pap) smear is widely accepted by both the public and health authorities as a useful tool for detection of cervical cancer and its precursors. In Israel only opportunistic screening exists and still the incidence of invasive cervical cancer is among the lowest in the world.

Objectives: To examine the existing evidence for the effectiveness of cervical cancer screening by Pap smears; to apply the findings to Israeli data, and to assess the implications for the current cervical cancer screening policy.

Methods: Search of Medline (1966-June 2003) and the Cochrane Library for relevant systematic reviews, controlled trials and cohort studies.

Results: There have been no trials of screening for cervical cancer and its precursors and therefore, no direct evidence that screening improves outcomes. A single retrospective cohort study estimated the age-adjusted RR for invasive cervical cancer in women with at least one Pap smear, whether normal or abnormal, compared to women with no smear at 0.4 (95% CI 0.2-0.9). In Israel some 27,800 (range: 20,800-167,000) women need to be screened in order to prevent one case of cervical cancer. The cost of preventing a single case of invasive cervical is approximately 1.288 million NIS (range: 1.643-13.193 million NIS).

Conclusions: An evidence-based approach to the question of the effectiveness of cervical cancer screening using Pap smears has yielded weak evidence. Based on this weak evidence and rough estimations of the effectiveness and cost of mass screening for cervical cancer in Israel, we conclude that the current policy should be maintained.

Cervical cancer; Screening; Pap; Evidence-based medicine; Number needed to screen (NNS)

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