Analysis of 172 Subtle Findings on Prior Normal Mammograms in Women with Breast Cancer Detected at Follow-up Screening

PURPOSE: To retrospectively review nonspecific findings on prior screening mammograms to determine what features were most often deemed normal or benign despite the development of breast cancer in the same location detected at follow-up screening. MATERIALS AND METHODS: Four hundred ninety-three pairs of consecutive mammographic findings were collected from 13 institutions, consisting of initial normal screening findings and a subsequent finding of cancer at screening (mean interval between examinations, 14.6 months). One designated radiologist reviewed each pair of mammograms and determined that 286 findings were judged visible at prior examination in locations where cancer later developed. Five blinded radiologists independently reviewed the prior findings in these 286 cases, identifying 169 mammograms (172 cancers) with findings so subtle that none or only one or two of the five radiologists recommended screening recall. Two unblinded radiologists reviewed the initial and subsequent findings and recorded descriptors and assessments for each finding and subjective factors influencing why, although the lesion was perceptible, it might have been undetected or not recalled. RESULTS: Of 172 cancers, 129 (75%) were invasive (112 T1 tumors and 17 T2 tumors or higher; median diameter, 10 mm), and 43 (25%) were ductal carcinoma in situ (median size, 10 mm). On the prior mammograms, 80% (137 of 172) of these cancers had subtle nonspecific findings where cancer later developed, and most were assessed as being normal or benign in appearance. CONCLUSION: There is a subset of cancers that display perceptible but nonspecific mammographic findings that do not warrant recall, as judged by both a majority of blinded radiologists and by unblinded reviewers. We believe failure to act on these nonspecific findings prospectively does not necessarily constitute interpretation below a reasonable standard of care.