Screening-preventable cervical cancer risks: evidence from a nationwide audit in Sweden.
BACKGROUND
The effectiveness of cervical cancer screening programs differs widely in different populations. The reasons for these differences are unclear. Routine and comprehensive audits have been proposed as an ethically required component of screening. We performed a nationwide audit of the effectiveness of the Swedish cervical cancer screening program.


METHODS
We identified all invasive cervical cancer cases that were diagnosed in Sweden from January 1, 1999, through December 31, 2001, and had been reported to the Swedish Cancer Registry (n = 1230 cases). We verified the diagnoses by histopathologic rereview and matched each case subject to five (population-based) age-matched control subjects who were identified from the National Population Register. The Pap smear screening histories for case and control subjects were reviewed for a 6-year period using the National Cervical Cancer Screening Register, which contains data on essentially all relevant cytological and histological diagnoses in Sweden. Odds ratios (ORs), and their 95% confidence intervals (CIs), of cervical cancer according to screening history were calculated in conditional logistic regression models. All statistical tests were two-sided.


RESULTS
Women who had not had a Pap smear within the recommended screening interval had higher risk of cervical cancer than women who had been screened (OR = 2.52, 95% CI = 2.19 to 2.91). This risk was similarly increased for all age groups (P(homogeneity) = .96). The risk for non-squamous cell cervical cancers (OR = 1.59, 95% CI = 1.20 to 2.11) was also increased. Women who had not had a Pap smear within the recommended screening interval had a particularly high risk of advanced cancers (OR = 4.82, 95% CI = 3.61 to 6.44). Among women who had been screened within the recommended interval, those with abnormal Pap smears had a higher risk of cervical cancer than those with normal smears (OR = 7.55, 95% CI = 5.88 to 9.69) and constituted 11.5% of all women with cervical cancer.


CONCLUSIONS
Nonadherence to screening intervals was the major reason for cervical cancer morbidity. The screening program was equally effective for women of all ages and was also effective against non-squamous cancers.
Andrae
Bengt
B
Department of Obstetrics and Gynecology, Gävle Hospital, S-801 87 Gävle, Sweden. bengt.andrae@gmail.com
Kemetli
Levent
L
Sparén
Pär
P
Silfverdal
Lena
L
Strander
Björn
B
Ryd
Walter
W
Dillner
Joakim
J
Törnberg
Sven
S
D000230:Adenocarcinoma / Q000175:diagnosis / Q000517:prevention & control; D000328:Adult; D002294:Carcinoma, Squamous Cell / Q000175:diagnosis / Q000517:prevention & control; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D015994:Incidence; D016015:Logistic Models; D008403:Mass Screening / Q000379:methods / Q000592:standards; D008485:Medical Audit; D008875:Middle Aged; D009367:Neoplasm Staging; D016017:Odds Ratio; D065006:Papanicolaou Test; D011322:Primary Prevention / Q000379:methods*; D015397:Program Evaluation; D012042:Registries; D018570:Risk Assessment; D012307:Risk Factors; D013548:Sweden / Q000453:epidemiology; D016312:Treatment Refusal; D002583:Uterine Cervical Neoplasms / Q000175:diagnosis* / Q000453:epidemiology / Q000473:pathology / Q000517:prevention & control*; D014626:Vaginal Smears