Hormone replacement therapy and screening mammography: analysis of the results in the Bouches du Rhone programme

Objective-To evaluate the effectiveness of a mass screening programme for b reast cancer in a French population where hormone replacement therapy (HRT) is common and where mammography is prescribed outside the programme for as ymptomatic women. Methods-From 1993 to 1996 inclusive, 41 062 women underwent a first test an d 48 275 a second or third test in the Bouches du Rhone programme. Their HR T status was ascertained at the time of the test. False positive and false negative tests were identified at one year follow up. The incidence of inte rval cancers was estimated up to three years after the screening test. Results-The odds of being detected at screening rather than as an interval cancer within one year of the test was five times greater among non-users o f HRT than among users (odds ratio (OR) 5.14 (confidence interval 2.5 to 11 .8)). This high reduction in sensitivity among users (71% v 92%) was associ ated with a very small reduction in specificity at the incident screen only . The incidence of interval cancers among HRT users was 3.5 times that of n on-users within the first year after the test and 1.7 times during the foll owing two years. Conclusions-When the early results of a programme have been used to measure its effectiveness they should be reassessed in populations where HRT is in widespread use. As interval cancers had better prognostic factors in HRT u sers than in non-users, the efficacy of a screening programme in such popul ations should be the subject of further studies.