Real-life effectiveness of screening programs can be very different from theoretical gains. Nationwide case-control audits with standard operating procedures and HPV data can be used for repeat evaluations over time, including whether implemented improvements work as expected and provide evidence for incremental improvements of programs and prioritization of QA efforts. In countries with efficient screening programs, most cervical cancers have been prevented (1). The residual morbidity represents cancer cases still encountered. To study the effect of the different elements in the screening process, and if there is need for new recommendations and guidelines, the analyses needed require linkage to registers and comparison with control subjects from the population and should be performed in a research setting using validated data (2).
In the updated Swedish national case control audit all 4273 cxca cases from 2002 to 2011 were clinically and histopathologically verified, and age-matched to 30 population-based controls in a nested case-control design. Complete screening histories for cases and controls were reviewed for a 10-year period using Swedish National Cervical Screening Registry (NKCx). Incidence rate ratios (IRRs), with 95% confidence intervals (CI), of cervical cancer according to screening history were estimated using conditional logistic regression models
Women with two negative Pap smear within two recommended screening intervals had a seven times lower risk of squamous cell carcinoma than women who had not been screened (IRR = 0.14, CI = 0.13 to 0.16). Risk for adenoca (IRR = 0.40, CI = 0.32 to 0.49) was also reduced. Risk was particularly reduced for advanced cancers (IRR = 0.10, CI = 0.09 to 0.13). For older women with repeat normal smears to and including age 60, risk for advanced cancer remains low for decades (IRR = 0.17, CI = 0.13 to 0.22). 12 percent of cases occurred in women with repeat normal smears. A majority of these were screen-detected micro-invasive cancers with a high chance of cure by conservative means of treatment (3)
The questions addressed by audits should be relevant and helpful for the responsible actors at the different levels of the screening program. They should address the organization to optimize participation, testing quality, screening test methods, triage, referrals, assessment, treatment, and follow up, as well as the authors of new guidelines. Issues regarding validity of the data should be addressed and evaluations should be comparable between countries. The standardized audit protocol will be repeated regularly to monitor effectiveness of changes, including upcoming switch to HPV-based primary screening
1. Vaccarella S. et al BJC 2014; 2. Andrae B. et al JNCI 2008; 3. Andrae B. et al BMJ 2012