PREVIOUS MAMMOGRAMS IN PATIENTS WITH IMPALPABLE BREAST-CARCINOMA - RETROSPECTIVE VS BLINDED INTERPRETATION

OBJECTIVE. We examined differences between blinded and retrospective r eviews of screening mammograms obtained before a mammogram that result ed in the diagnosis of an impalpable breast carcinoma. MATERIALS AND M ETHODS. We reviewed 152 previous mammograms in 73 patients in whom imp alpable breast carcinomas were subsequently detected on later mammogra ms. The earlier studies were interpreted in two ways: (1) blindly (wit hout knowledge that carcinoma was subsequently detected) and (2) retro spectively (with the mammogram showing the carcinoma for comparison). The two interpretations were then compared with regard to the presence of carcinoma, recommendations for biopsy, parenchymal density, histol ogic characteristics of the tumor, lymph node status, and film quality . RESULTS. When we did a blinded review of the mammograms obtained bef ore the diagnostic mammograms, the previous study was interpreted as s howing evidence of carcinoma in 30 patients (41%). For the remaining 4 3 patients (59%), the findings on the most-recent previous mammogram w ere interpreted as normal or benign by the blinded reviewers; however, the retrospective reviewers thought evidence of cancer was visible in 25 of these patients (34%). Differences between blinded and retrospec tive interpretations were statistically significant. In patients in wh om evidence of tumor was thought to be present on retrospective review but not on blinded review, the majority of mammographic abnormalities were asymmetric densities on the most-recent previous examination. Th is was true whether or not the retrospective reviewers thought that th e mammographic finding warranted earlier biopsy. The histologic charac teristics and lymph node status among patients in whom mammograms were interpreted retrospectively as showing evidence of tumor were no diff erent from those among patients with no evidence of tumor. CONCLUSION. Our results show that impalpable breast carcinomas are frequently evi dent in retrospect on previous mammograms. However, because many are m anifested only as an asymmetric density, these may not necessarily be true radiologic errors. Failure to detect a retrospectively visible ab normality on a screening mammogram is not necessarily negligent, and r etrospective reviews do not reflect the everyday practice of screening mammography.