Hormone Receptor-Positive Encapsulated Papillary Carcinoma of the Breast With High-Grade Cytological Features: A Case Report With Invasive Heterogeneity.

BACKGROUND Encapsulated papillary carcinoma (EPC) with high-grade cytological features of the breast is an uncommon neoplasm characterized by aggressive biological behavior, histopathological heterogeneity, and a potential for invasion. Although typical EPCs usually present as low- to intermediate-grade lesions, those with high-grade cytological features are rare and poorly described in the literature. The diagnostic challenge lies in distinguishing these tumors from invasive papillary or ductal carcinomas and determining appropriate management strategies. CASE REPORT We describe the case of a 40-year-old woman who presented with a palpable lump in her right breast. Initial ultrasonography revealed a well-circumscribed 23-mm mass interpreted as benign, but follow-up imaging after 3 months showed rapid enlargement to 30 mm. Core needle biopsy confirmed invasive breast carcinoma of no special type. The patient underwent a skin-sparing mastectomy with immediate reconstruction. Histopathological examination revealed an EPC with high-grade cytological features, accompanied by high-grade and low-grade invasive components beyond the fibrous capsule. Immunohistochemically, the tumor was strongly positive for estrogen and progesterone receptors, negative for human epidermal growth factor receptor 2 (1+), and showed a high Ki-67 index (46.5%). The patient received adjuvant endocrine therapy and remains disease-free at the most recent follow-up. CONCLUSIONS This case illustrates the diagnostic and biological heterogeneity of hormone receptor-positive EPC with high-grade cytological features. Recognition of invasive components and accurate histopathological assessment are critical for proper classification and management. Given the presence of high-grade atypia, high mitotic activity, and a high proliferation index, such tumors should be managed according to the principles of invasive breast carcinoma.