[Reversed polarity high-cell carcinoma of the breast: A case report].

Reverse polarity high-cell carcinoma of the breast, formerly known as reverse polarity solid papillary carcinoma, is a rare entity recently introduced into the latest edition of the WHO classification of breast tumors. Its phenotype is triple-negative, and its diagnosis difficult. Although few cases have been reported in the literature, knowledge of this breast tumor is essential to distinguish it from other triple-negative carcinomas, which have a poorer prognosis. We report a case of high-cell, inverted-polarity carcinoma of the breast in a 43-year-old female patient with no history of breast neoplasia and no palpable mass on clinical examination. The tumour was discovered following a screening echomammogram, which revealed a lesion classified ACR 4b. A microbiopsy of this lesion concluded that it was a papillary proliferation that should be removed. A lumpectomy was performed. Histopathological and immunohistochemical studies of the surgical specimen confirmed the diagnosis of high-cell, reverse-polarity carcinoma expressing calretinin and IDH1. Given the rarity of this entity, there is no standard treatment. In our case, a mastectomy without lymph node curage was performed. The extension work-up was negative and the patient received no adjuvant treatment. After 12 months, the patient is in complete remission. In this case report, we describe the histopathological, immunohistochemical and molecular features of this rare entity.