Tall Cell Carcinoma of Reversed Polarity: Case Report of a Rare Breast Lesion

Tall cell carcinoma of reversed polarity is a very rare subtype of carcinoma with low systemic dissemination potential and an indolent course. It has been recently been described in the WHO Blue Book as a special type of invasive breast carcinoma with a characteristic molecular profile, also known as 'breast tumour resembling tall cell variant of papillary thyroid carcinoma' due to their similarity with tall cell variant of papillary thyroid carcinoma. While it morphologically overlaps with papillary thyroid carcinoma, this primary breast carcinoma does not express thyroid-specific markers. In the early literature, all reported TCCRP cases were in situ lesions; however, the 2019 Classification of Breast Tumours clearly categorizes TCCRP as a rare subtype of invasive breast adenocarcinoma. Since its first report in the literature by Eusebi et al., it is thought that up to 80 cases of TCCRP have been reported, all of which occurred in women. It has a particular immunohistochemistry profile that allows its distinction from thyroid cancer metastasis and additionally this tumour is associated with a characteristic hotspot mutation R172 in the IDH2 gene, which is otherwise rare in breast carcinomas. We present the case of a 34-year-old female patient and correlate our findings with previously reported cases in the literature.