Encapsulated papillary carcinoma with invasion in the breast: A case report with imaging findings.

Encapsulated papillary carcinoma (EPC) of the breast is a rare subtype of papillary carcinoma. EPC with invasion has a higher rate of axillary lymph node metastasis than noninvasive EPC; thus, it is important to assess the presence of invasion using preoperative radiologic imaging. However, there are few comprehensive studies on its imaging characteristics. Herein, we present the case of a 58-year-old woman who noticed a lump in her right breast 2 weeks prior to presentation. Imaging revealed a cystic tumor with solid components, abundant blood flow, and findings suggestive of extracapsular invasion, including a hyperechoic halo on ultrasound and a linear enhancement extending toward the nipple on enhanced MRI. Core needle biopsy diagnosed ductal carcinoma in situ; however, histopathology after total mastectomy confirmed EPC with invasion. The tumor was ER-positive (100%), PgR-positive (60%), and HER2-negative, with a Ki-67 index of 10% and histological grade of 1. The patient underwent axillary lymph node dissection due to macrometastasis, and immediate breast reconstruction with a muscle-preserving deep inferior epigastric perforator (mp-DIEP) flap was performed. Postoperative recovery was uneventful, and she remained recurrence-free on tamoxifen therapy for 2 years. This case highlights key imaging features suggestive of invasion in EPC, which may facilitate preoperative assessment and management.