However the researcher leading the study, Mrs Hege Wang MSc., is cautious about describing such tumours as “missed” cancers.
Six radiologists looked at a total of 723 mammograms, of which 350 either had cancers that had been detected during screening (118) or had cancers detected in the period between screenings (interval cancers).
Although it was a “blinded” review (they did not know in advance whether the mammogram showed a tumour or not), the radiologists did know that about 50% of the cases were either cancers or subsequent interval cancers, and therefore that they would have to select a high number of cases.
Mrs Wang, a researcher with the Norwegian Cancer Registry, said: “The experimental set-up is very different from the daily work of screening radiologists. In the normal daily routine, only three to five per cent of mammograms are recalled for suspected cancer, and it is very important not to have too high a recall rate in screening in order to avoid false positive results. So the fact that retrospectively the radiologists detected 27% of previously undetected cancers does not necessarily mean that they were missed. The figure of 27% corresponds to about 5% of the total number of breast cancers detected amongst these women during this period.”
Results from the study showed that 50% of lesions were not selected by any of the radiologists, 23% were selected by one or two, and 27% by three or more.
Mrs Wang said: “Reviewing interval cancers is complicated but sensible and important. The data must be interpreted with care. There is no simple way of classifying an interval cancer as missed, however, based on these results, it is reasonable to conclude that 27% of the lesions could have been detected during screening.”
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