Tall cell carcinoma with reversed polarity – a case report

Abstract

Tall cell carcinoma with reversed polarity is a rare subtype of invasive breast carcinoma. Immunohistochemical and molecular research show that it is a distinct entity. It is negative for thyroid specific markers.1 It also has its own unique molecular mutations (IDH2 hotspot mutations and PI3K pathway mutations).2 We present a case of tall cell carcinoma with reversed polarity in the breast of an 81-year-old woman. The lesion showed papillary morphology and columnar cells exhibiting reversed nuclear polarity. Immunohistochemistry showed the tumour cells were positive for CK5/6. They showed weak positivity for GATA3 and GCDFP and were negative for TTF-1. Stains for p63 and p40 showed an absence of myoepithelial cells around tumour nests. The core biopsy showed triple negative hormone receptor status. Further molecular testing was performed which showed a mutation in the PIK3CA gene. An activating mutation in the IDH2 gene was also detected. The combination of morphologic, immunohistochemical and molecular findings are diagnostic of tall cell carcinoma with reverse polarity. It can present a diagnostic challenge when encountered. IDH2 and PI3K mutation testing may provide more confidence with diagnosing these lesions and to help distinguish it from other breast neoplasms. 1.WHO Classification of Tumours Editorial Board. WHO Classification of Tumours: Breast Tumours. 5th ed. Lyon: IARC, 2019.2.Zhong E, Scognamiglio T, D'Alfonso T, et al. Breast tumour resembling the tall cell variant of papillary thyroid carcinoma: molecular characterization by next-generation sequencing and histopathological comparison with tall cell papillary carcinoma of thyroid. Int J Surg Pathol 2019; 27: 134–41.