A study of breast cancers detected in the incident round of the UK NHS Breast Screening Programme: the importance of early detection and treatment of ductal carcinoma in situ.

One hundred and seventy eight cancers detected on incident round screening in the UK National Health Service Breast Screening Programme were reviewed. Critical review of the immediately preceding screening films (from 3 years previously) found abnormalities at the site of the subsequently detected cancer in 93 cases (52%). Forty-eight of these (27% of the total) had microcalcification as the sole abnormality. All of these 48 women had invasive ductal carcinoma and/or ductal carcinoma in situ (DCIS) (including four cases in which DCIS was associated with another type of primary invasive breast cancer). The finding of microcalcification on the previous mammograms at the site of a subsequently detected cancer was a strong predictor for the presence of DCIS (with or without associated invasive disease) (P<0.0001). Of the women with invasive ductal carcinoma, those with microcalcification on previous films were significantly more likely to have intermediate or high grade (grade 2 or 3) tumours than those women without microcalcification on previous films (P=0.0015). Previous films were also read blind by two independent experienced breast radiologists. Cancers were correctly identified by one or both readers in 39 cases. However, 35 of the remaining 139 cases showed microcalcification which was not detected or considered significant by the readers. If only these 139 'true negative' screens are analysed, similar associations are seen between microcalcification on previous films and subsequent finding of DCIS (P=0.03) and between microcalcification on previous films and high grade invasive ductal carcinomas (P=0.015). These findings provide support for the hypothesis that microcalcification seen on previous screening films at the site of a subsequently detected invasive ductal carcinoma represents ductal carcinoma in situ. In this series, 19 of 82 women (23%) with invasive ductal carcinoma in the 'true negative' screen group had microcalcification suggestive of DCIS on mammograms taken, on average, 3 years previously. Significant microcalcification is often overlooked using current detection criteria. Early detection and treatment of DCIS is essential in order to prevent the development of aggressive invasive disease. Revision of the NHSBSP targets for DCIS detection is recommended.