Pure flat epithelial atypia (DIN 1a) on core needle biopsy: study of 60 biopsies with follow-up surgical excision.

Flat epithelial atypia (FEA) is recognized as a precursor of breast cancer and its management (surgical excision or intensive follow-up) remains unclear after diagnosis on core needle biopsy (CNB). The aim of this study was to determine the underestimation rate of pure FEA on CNB and clinical, radiological, and pathological factors of underestimation. 4,062 CNBs from 5 breast cancer centers, performed over a 5-year period, were evaluated. A CNB diagnosis of pure FEA was made in 60 cases (1.5%) (the presence of atypical ductal hyperplasia, lobular neoplasia, radial scars, phyllodes tumor, papillary lesions, ductal carcinoma in situ or invasive carcinoma at CNB were exclusion criteria), and subsequent surgical excision was systematically performed. The histological diagnosis was retrospectively reviewed using standardized criteria and the precise terminology of the World Health Organization by two pathologist physicians. At surgical excision, 6 (10%) ductal carcinoma in situ and 2 (3%) invasive carcinoma were diagnosed. The total underestimation rate was 13%. FEA was associated with atypical ductal hyperplasia in 10 (17%) cases and with lobular neoplasia in 2 (3%) at final pathology. Residual FEA was found in 14 (23%) cases. No clinical, radiological or pathological factors were significantly associated with underestimation. Our data highlight the importance of recognizing and diagnosing FEA in core needle biopsies. Thus, the presence of FEA on CNB, even in isolation, warrants follow-up excision.