Encapsulated Papillary Carcinoma and Its Differential Diagnosis from Triple-negative Breast Cancer: a retrospective analysis

Background : Encapsulated papillary carcinoma (EPC), a rare breast malignancy, shares overlapping MRI characteristics with triple-negative breast cancer (TNBC), posing significant diagnostic challenges in radiological differentiation. Therefore, This study aimed to differentiate EPC from TNBC based on clinical and MRI characteristics. Methods : This retrospective study included 42 patients with histopathologically proven breast cancer (EPC:17, TNBC:25) who underwent breast MRI. The clinical, pathological, and MRI characteristics were systematically examined between the two groups. Results : Clinical characteristics and MRI findings can provide useful information for the differentiation between EPC and TNBC. Significant differences were observed in onset age, MRI features (shape, lobulated sign, spiculated sign, low-signal circular sign on T2WI, hemorrhage, necrosis, cystic degeneration, mass configuration, and mural nodule), axillary lymph node metastasis, and Ki67 expression. No statistical differences were found in nipple discharge or other MRI features (number of lesions, position, maximum tumor diameter, peritumoral edema/effusion, duct dilatation, internal enhancement characteristics, time-intensity curve, or mean ADC value). Compared to TNBC, EPC more frequently presented as a cystic or cystic-solid mass with round/oval shape, cystic degeneration, mural nodules, and a low-signal circular sign on T2WI. Hemorrhage was observed in ~35% (6/17) of EPC cases, while necrosis was rare. . Conclusion :The combination of patient age and MRI characteristics provides valuable diagnostic differentiation between EPC and TNBC, contributing valuable clinical insights to preoperative assessment and clinical decision-making for the rare disease.