A case-control study of cervical cytology before diagnosis of cervical cancer in Denmark.

The number of previous vaginal smear examinations in 428 patients who developed invasive cancer of the cervix was compared with previous screening in age- and area-matched controls. The average age was 53 years. There was a highly significant difference in the numbers who had never undergone screening, ie 55% of the cancer patients and 33% of the controls. Equally there was a highly significant difference between cases and controls in the number examined according to recommended guidelines for prophylactic examination. It was shown that about 40% of the cytological tests were done for gynaecological reasons, and it is probable that the number of false negatives among the cases was not negligible. Despite this, however, regular screening reduced the relative risk of cancer to about 0.25, compared with those never examined. When only symptomless patients were considered in the assessment of regular screening, the relative risk was reduced to 0.15 in patients screened every three years. Even the group which was screened more than five years previously had a relative reduction in risk to 0.67, compared with those never screened. It is concluded that PAP-smears are important in the prevention of cancer of the cervix. The greatest need is to eliminate the group which is never examined. An increase in the number of screenings has only a marginal benefit.