Objective: To evaluate breast cancer underestimation rate of atypical ductal hyperplasia (ADH) diagnosed by core-needle biopsy (CNB) under imaging guidance in Ramathibodi Hospital and to determine the difference between the malignant and benign groups in terms of clinical and imaging characteristics.
Material and Method: The pathological records of 1,521 patients who underwent CNB under imaging guidance were reviewed. Thirty-nine patients diagnosed with ADH were enrolled into the present study. Clinical data, imaging features, biopsy technique and result of excisional biopsy as well as follow-up data were retrospectively reviewed.
Results: Of 39 ADH cases, eight (20.5%) were found to have malignancy on subsequent excisional biopsy. The majority of these were ductal carcinoma in situ (DCIS) (62.5%). Lesion categorized as category 5 according to BI-RADS (Breast imaging reporting and data system) was the only feature which was statistically different between the benign and malignant groups. No statistically significant difference was found between the benign and malignant groups in terms of age, personal and family history of breast cancer, clinical finding, mammographic lesion type, size of lesion, image-guided technique and percentage of lesion removal.
Conclusion: The underestimation rate of ADH in the present study was comparable to other studies. The finding of BI-RADS category 5 in patients with ADH diagnosed from CNB is a strong indication for subsequent excisional biopsy.

Keywords: Breast biopsy, Core-needle biopsy, Imaging-guided biopsy, Stereotactic biopsy, Atypical ductal hyperplasia