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Purpose: The need for surgical excision in patients with ultrasound-guided core needle biopsy (CNB)-diagnosed atypical ductal hyperplasia (ADH) remains an issue of debate. The present study sought to validate a scoring system (the U score, for underestimation) that we have previously developed for predicting malignancy in CNB-diagnosed ADH. Methods: The study prospectively enrolled 85 female patients with CNB-diagnosed ADH who underwent subsequent surgical excision. Underestimation was defined as a surgical specimen having malignant foci. Results: The overall underestimation rate was 37% (31/85). Multivariate analysis showed that a clinically palpable mass, microcalcification on imaging, size > 15 mm and a patient age of ≥ 50 years were independently associated with underestimation. When applied to the scoring system, the validation score was significant (p< 0.001; area under the curve, 0.852). No patient with a U score < 3.5 had an underestimated lesion. Conclusion: The present study successfully validated the efficacy of our scoring system for predicting malignancy in CNB-diagnosed ADH. A U score of ≤ 3.5 indicates that surgical excision may not be necessary.

Breast core needle biopsy (CNB) is an established method for diagnosing benign and malignant breast disease and CNB is widely used in daily practice. However, CNB samples only part of a lesion, and this can be the reason for an inaccurate diagnosis.(1) This size limitation of CNB gives rise to important diagnostic problems because one of the important factors for making the differential diagnosis between atypical ductal hyperplasia (ADH) and lowgrade ductal carcinoma in situ (DCIS) is the size of the lesion.(2,3) Previous studies have reported that ADH in a CNB showed significant discordance in the subsequent surgical excision specimens for which 33-87% demonstrated ductal carcinoma such as DCIS and invasive ductal carcinoma (IDC).(4-11) Therefore, surgical excision is presently recommended when ADH is diagnosed in a CNB. Investigations to determine the factors that are predictive of more advanced lesions in surgical excision specimens when ADH was diagnosed in the CNB have suggested cytologic atypia,(11) more than 4 foci (7) and micropapillary architecture (7), yet consistent results were not demonstrated. The purpose of this study was to identify the predictive factors that suggest the diagnosis of ductal carcinoma in the subsequent surgical excision specimens when ADH is diagnosed in a CNB.