ESTIMATING THE EFFICACY OF SCREENING BY AUDITING SMEAR HISTORIES OF WOMEN WITH AND WITHOUT CERVICAL-CANCER

The screening histories of all 348 women with invasive cervical cancer diagnosed in 1992 in 24 self-selected district health authorities and health boards in England, Wales and Scotland were compared with those of 677 age- and residency-matched controls. The controls were randoml y selected from the family health services authority (FHSA) register. Screening histories, comprising the dales and results of all smears ta ken before the date of diagnosis of the patient's cancer, were determi ned from the FHSA computer and laboratory records. We estimate that th e number of cases of cervical cancer in participating districts in 199 2 would have been 57% (95% confidence interval 28-86%) greater if ther e had been no previous screening. In women under the age of 70 it woul d have been approximately 75% (31-115%) greater. Extrapolation of the results from this pilot suggests that screening prevented between 1100 and 3900 cases of invasive cervical cancer in the UK in 1992. Women w ith stage 1B cancer or worse were more likely to have no record of pre vious screening than controls: 47% of these women under the age of 70 had been adequately screened according to current (5 yearly screening) guidelines, compared with 75% of matched controls. Thirteen per cent of all patients under age 70 had screening histories indicative of ina dequate follow-up of smears requiring colposcopy. The proportion of mi croinvasive cases with screening predating diagnosis was similar to th e proportion of controls. There was a strong correlation between stage and age: 56% of cancers in women under 35 were microinvasive compared with just 9% in women 65 years or over. The 'relative protection' fol lowing a negative smear was greatest in the first 12 months and fell o ff towards the end of the fifth year. These data suggest that full adh erence to current guidelines could perhaps have prevented another 1250 cases, but additional steps would have been required to prevent some of the 2300 remaining cases in women under the age of 70.