Tall cell carcinoma with reversed polarity: case report of a rare special type of breast cancer and review of the literature.

Tall cell carcinoma of the breast with reversed polarity (TCCRP) is a rare and diagnostically challenging subtype of triple-negative invasive breast carcinoma. Herein, we report a case of a 60-year-old female presenting with a two-year history of a left breast mass that exhibited progressive enlargement. Histopathological examination of the excised tumor revealed distinctive morphological features, including expansive nests of neoplastic cells with sharply demarcated borders and a spectrum of architectural patterns encompassing solid, follicular, and papillary configurations. Notably, papillary structures contained delicate fibrovascular cores infiltrated by foamy macrophages. The tumor cells demonstrated characteristic tall columnar to cuboidal morphology with nuclei displaying reversed polarity (basal-to-luminal nuclear polarization). Immunophenotypic analysis revealed a triple-negative profile (ER -/PR -/HER2 -) with co-expression of CK5/6 and GATA-3, while P63 staining confirmed the absence of myoepithelial differentiation. Molecular characterization identified an IDH2 p.R172S hotspot mutation, further corroborating the diagnosis. This case underscores the importance of integrating histomorphological features, immunohistochemical profiles, and molecular biomarkers to distinguish TCCRP from other triple-negative breast carcinomas. Recognition of this indolent entity is critical for avoiding overtreatment and ensuring appropriate clinical management, given its favorable prognosis compared to conventional triple-negative breast cancers.