Women who do not undergo regular cervical cancer screening tests are more likely to be diagnosed with the disease than those who do, according to an audit of the Swedish national cervical cancer screening program that will be published online April 29 in the Journal of the National Cancer Institute. Participation in screening reduces the risk for all types of cervical cancers in all ages. Better follow-up of the women who are screened could further reduce cervical cancer rates, the researchers concluded.
Cervical cancer screening programs reduce the incidence of disease, but the effectiveness of such programs varies among populations. Regular audits of screening programs are valuable because they provide insight into how a program works and how it might be improved.
In this nationwide caseâ€"control study, Bengt Andrae, M.D., and colleagues of the GÃ¤vle Hospital and the Karolinska Institute in Sweden compared the rates of cervical cancer diagnosis in women who had been screened and those who had not. Using data from the Swedish Cancer Registry and from the National Cervical Cancer Screening Registry, the researchers identified 1,230 cervical cancer patients who were diagnosed between 1999 and 2001, and 6,124 age-matched control subjects, from the population register, who had not been diagnosed with cervical cancer.
Women who had not had a Pap smear screening test within the recommended 3-year interval were 2.5 times as likely to be diagnosed with cervical cancer as women who had Pap tests regularly. These women were also nearly 5 times as likely to be diagnosed with advanced disease as those who were screened. Participation in screening reduced the risk for all types of cervical cancer and reduced the risk of women between twenty-three and thirty; these were both novel findings.
Screening did not completely protect women from cervical cancer diagnoses, however. Women who were screened within the recommended interval and found to have abnormal cells had a 7.6-fold increased risk of developing cancer compared with women who were screened and had normal results. Women with abnormal Pap results accounted for 11.5 percent of all of the cervical cancer cases. This risk increase was, however, not seen for advanced cancers.
The study highlights the role of population-based registers in uncovering the reasons for the continued incidence of cervical cancer despite organized screening programs. As expected, imperfect population coverage of screening was by far the most important risk factor for incident cervical cancer. Abnormal smears, particularly if not followed up by a biopsy, were also an important risk factor, which suggests that improved follow-up programs are warranted. On the other hand, it was possible to demonstrate a beneficial effect of screening in younger women and against cancers of the cervix.
In an accompanying editorial, Jack Cuzick, Ph.D., of the Cancer Research UK Centre in London emphasizes the importance of systematic audits of screening cancer programs. "Audits, such as the one described by Andrae [and colleagues], need to become routine within screening programs if screening is to achieve its full potential," Cuzick writes. Such reviews identify ways in which the screening program has failed and point out opportunities where the system needs to be retooled and improved.
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