THE DETECTABILITY OF BREAST-CANCER BY SCREENING MAMMOGRAPHY

We reviewed 134 patients with breast cancer (screen detected = 85, int erval = 49) who had been reported as negative at previous mammographic screening in the Florence District Programme. At prior mammograms rev iew, 12% of the cases were classified as 'screening error' (suspicious signs missed owing to misperception or poor imaging technique), 26% a s 'minimal signs present', 54% as 'radiographically occult' and 7% as 'radiographically occult at diagnosis'. These results are quite consis tent with those recently reported for the Nijmegen screening programme . Screening errors may be reduced either by reducing the risk of mispe rception (double reading) or by improving imaging quality, but this wo uld achieve earlier detection in a minority of cancer cases. Minimal s igns of cancer were present 2 years before the diagnosis in over one-t hird of screen-detected cancers. Increasing screening frequency (from biennial to annual) may advance detection time of most 'screening erro rs' and of some cancers in the 'minimal signs present' and 'mammograph ically occult' categories, but this would almost double screening cost s, and the benefit would probably be inferior to that obtained by doub ling the population invited to biennial screening. Adopting less strin gent criteria for referral to diagnostic assessment would probably lea d to the detection of some cases in the 'minimal signs present' catego ry. This seems to us a more convenient policy to adopt to advance canc er detection time, although it will also sharply increase referral rat es and costs. As diagnostic assessment of minimal lesions is far from being 100% accurate, this policy would also considerably increase the frequency of unnecessary benign biopsies. All these negative effects m ight turn out to be unacceptable.