[Case-control study of the effectiveness of mass screening in reducing invasive cervical cancer]

A case-control study was conducted in Miyagi Prefecture, Japan, to evaluate the effectiveness of mass screening for invasive cervical cancer. The Papanicolaou (Pap) smear histories of 109 cases with invasive cervical cancer diagnosed in the years 1984-1989 were compared with those of 218 age (+/- 3 years)- and area-matched controls. Fifty-five percent of 109 cases were screened at least once, while for the controls the figure was 85.5%. Compared with women who were never screened, the odds ratio of invasive cervical cancer for women screened at least once was 0.16 [95% confidence interval: 0.090-0.278]. The odds ratio for 98 cases with squamous cell carcinoma for screened versus never screened women was 0.14 [0.080-0.253]. The Pap smear was less effective as a screening procedure for adenocarcinoma of the cervix than for squamous cell carcinoma. Of 11 cases with adenocarcinoma, 81.8% were screened, compared with 90.9% of controls. The odds ratio was 0.45 [0.054-3.719]. It showed that the odds ratio for the 1-year interval between last normal smear and diagnosis was 0.11 [0.061-0.196] and that for the 2-year intervals was 0.33 [0.157-0.714]. From the results of our study, it can be concluded that mass screening is effective for invasive cervical cancer.