Encapsulated Papillary Carcinoma of the Breast: Two Cases with Literature Review and Molecular Insights.

Encapsulated papillary carcinoma (EPC) of the breast is a rare subtype of breast cancer, accounting for 0.5-2% of cases, and typically affects postmenopausal women. Characterized by well-circumscribed lesions lacking peripheral and central myoepithelial cells, EPC is associated with favorable prognosis due to its indolent behavior and high hormone receptor positivity. However, its potential association with ductal carcinoma in situ (DCIS) or invasive carcinoma necessitates thorough diagnostic evaluation. This study presents two cases of EPC-one in a 57-year-old and the other in a 39-year-old female-each with focal DCIS and strong estrogen and progesterone receptor expression. Both patients underwent breast-conserving surgery and were managed with hormone therapy. Histopathological and immunohistochemical analyses confirmed the EPC diagnosis, and molecular insights revealed common mutations, particularly in the PIK3CA gene. This report underscores the importance of integrating clinical, histological, and molecular findings to guide diagnosis and management of EPC, which, despite its low invasive potential, shares genetic features with invasive ductal carcinoma.