Marked Unilateral Breast Enlargement Caused by a Fibroepithelial Lesion Suspicious for Phyllodes Tumor in the Modern Screening Era: A Case Report and Literature Review.

Markedly enlarged fibroepithelial breast lesions have become increasingly uncommon in the modern era of routine breast imaging and earlier diagnostic evaluation. We report the case of a 52-year-old woman who presented with progressive unilateral right breast enlargement and pain after delaying evaluation despite previously abnormal breast imaging. Clinical examination demonstrated marked right breast enlargement without overt inflammatory or infectious changes. Ultrasound-guided core needle biopsy revealed a fibroepithelial lesion with benign phyllodes tumor included in the differential diagnosis; however, definitive histologic classification required excisional pathology. Given the extensive breast involvement and limited feasibility of breast-conserving surgery, the case was reviewed by a multidisciplinary team, and total mastectomy was recommended. At the time of manuscript preparation, the patient was still considering surgical management, and definitive excisional pathology and long-term follow-up were unavailable. This case highlights the uncommon contemporary presentation of a markedly enlarged fibroepithelial breast lesion despite advances in breast screening and emphasizes the diagnostic limitations of core needle biopsy, the importance of multidisciplinary evaluation, and the consequences of delayed medical assessment on subsequent management.