Preoperative Diagnosis of Ductal Carcinoma In Situ Arising Within a Mammary Fibroadenoma: A Case Report

Fibroadenoma is the most common form of benign breast tumor and the most common breast tumor in women under 30 years of age. However, carcinoma arising within a fibroadenoma is unusual, with over 100 cases reported in the literature. Histological diagnosis is typically unexpected. A 46-year-old female with no family history of breast malignancies was admitted for an elastic hard lump in the upper-outer quadrant of her right breast. At a clinic that she visited previously, her condition was diagnosed by core needle biopsy with four specimens showing fibroadenoma with borderline atypical ductal hyperplasia at pathology. Excisional biopsy was recommended for pathological diagnosis. The patient requested a definitive diagnosis and alternative treatment to tumorectomy. More biopsy specimens were needed for pathological diagnosis; therefore, ultrasonography-guided vacuum-assisted core needle biopsies were obtained, confirming ductal carcinoma in situ with questionable microinvasion of intracanalicular- and pericanalicular-type fibroadenoma. Right breast-conserving surgery and sentinel lymph node biopsy were immediately performed for radical therapy. We present this case to increase awareness of this entity and stress the need for histological evaluation of some breast masses.