Abstract
INTRODUCTION AND IMPORTANCE: Tall cell carcinoma with reverse polarity (TCCRP) is a rare and newly recognized subtype of invasive breast carcinoma, first described in 2003. It shares histological similarities with tall cell papillary thyroid carcinoma, characterized by papillary structures with reverse cellular polarity. Due to its rarity, TCCRP has been poorly understood, and fewer than 100 cases have been reported globally. This report presents the first case of TCCRP in South Tunisia, contributing to the growing body of knowledge regarding this rare tumor. CASE PRESENTATION: A 34-year-old woman with no significant personal or family history of breast cancer presented with an incidental finding of a 1 cm breast mass. Imaging studies revealed an atypical mass classified as ACR 4a. Histological analysis following lumpectomy showed circumscribed nests of epithelial cells with delicate fibrovascular cores, resembling papillary structures. Immunohistochemical staining revealed diffuse positivity for cytokeratin 5/6 and calretinin, and negativity for estrogen, progesterone, HER-2, and TTF1. The diagnosis of TCCRP was confirmed. The tumor was classified as SBR grade I, with no lymphovascular invasion or carcinoma in situ. No metastasis was observed in the 31 axillary lymph nodes. CLINICAL DISCUSSION: TCCRP primarily affects women over 60, with a low incidence in younger individuals. It typically presents as a small, palpable breast mass. Histologically, TCCRP exhibits a solid-papillary architecture with tall cells, reverse polarity, and rare foamy histiocytes. Immunohistochemical findings include negative estrogen, progesterone, HER-2, and TTF1 markers, along with positive staining for calretinin. Molecular studies have revealed IDH2 and PIK3CA mutations in the majority of cases. Despite being triple-negative, TCCRP has a favorable prognosis, with low rates of metastasis or recurrence. CONCLUSION: TCCRP is a rare subtype of invasive breast carcinoma with distinct histological and immunohistochemical features. It is characterized by an indolent clinical course and an excellent prognosis. Conservative surgical management with clear margins is the optimal treatment approach, with no clear indications for lymph node dissection, chemotherapy, or radiotherapy.