Ductal Carcinoma In Situ in a Complex Fibroadenoma

Abstract

Fibroadenomas are common benign breast lesions in young women, whereas carcinoma arising within a fibroadenoma is exceptionally rare and is usually identified incidentally following excision. Preoperative recognition can be challenging because clinical and imaging appearances may remain largely benign and small malignant foci may not be captured by core needle biopsy. We report an uncommon presentation of low-grade ductal carcinoma in situ (DCIS) arising within a complex fibroadenoma in a 29-year-old woman. The patient presented with an enlarging palpable breast mass demonstrating interval growth and mild sonographic heterogeneity. Core needle biopsy showed a fibroadenomatous lesion with adenosis but no atypia or malignancy. Excision was undertaken because of the lesion’s interval growth and atypical features, and histopathological examination demonstrated low-grade cribriform DCIS with atypical ductal hyperplasia confined within a complex fibroadenoma, with clear margins and no invasive disease. Following multidisciplinary assessment, observation without adjuvant therapy was recommended. This case highlights the diagnostic limitations of core biopsy in an enlarging or atypical fibroadenoma and the importance of clinical, radiological and pathological correlation when determining the need for excision. Although rare, in situ carcinoma should remain a diagnostic consideration when a presumed fibroadenoma demonstrates discordant or changing features.