CONSISTENCY OF HISTOPATHOLOGICAL REPORTING OF BREAST-LESIONS DETECTEDBY SCREENING - FINDINGS OF THE UK NATIONAL EXTERNAL QUALITY ASSESSMENT (EQA) SCHEME

The aim of the scheme was to determine consistency of histopathologica l reporting in the United Kingdom National Breast Screening Programme. This external quality assessment scheme involved 51 sets of 12 slides which were circulated to 186-251 pathologists at intervals of 6 month s for 3 years. Participants recorded their diagnoses on standard repor ting forms, which were submitted to the U.K. National Cancer Screening Evaluation Unit for analysis. A high level of consistency was achieve d in diagnosing major categories of breast disease including invasive carcinoma and the important borderline lesions, radial scar and ductal carcinoma in situ (DCIS), the latter exceeding a national target set prior to the onset of the scheme. Atypical hyperplasia (AH) was report ed with much less consistency although, where it was the majority opin ion, over 86% of diagnoses were of benign disorders and only 14% were of DCIS. Inconsistency was encountered in subtyping and measuring DCIS , the former apparently due to current uncertainties about classificat ion and the latter to poor circumscription, variation in size in diffe rent sections and merging with zones of AH. Reporting prognostic featu res of invasive carcinomas was variable. Measurement of size was achie ved with adequate consistency except in a small number of very poorly circumscribed tumours. Grading and subtyping were inconsistent althoug h the latter was not specifically tested and will be the subject of fu ture study. Members of the National Coordinating Group achieved greate r uniformity than the remainder of the participants in all diagnostic categories, but both groups experienced similar types of problem. Our findings suggest that participation in the scheme improves diagnostic consistency. In conclusion, consistency in diagnosing invasive carcino ma and radial scar is excellent, and good in DCIS, but improvements ar e desirable in diagnosing atypical hyperplasia, classifying DCIS and r eporting certain prognostic features of invasive tumours. Such improve ments will require further research, the development of improved diagn ostic criteria and the dissemination of clearer guidelines.