Solid-papillary carcinoma with reverse polarity (SPCRP) harboring a novel IDH1 R132C mutation: A case confirming the expected IDH1/IDH2 dichotomy

Solid-papillary carcinoma with reverse polarity (SPCRP) is a rare subtype of breast cancer characterized by the distinct histological finding of solid-papillary architecture with a perivascular pseudorosette-like pattern of so-called “reverse” nuclear polarity, a predominantly triple-negative biomarker profile and recurrent hotspot mutations in IDH2 R172. It is well-known that many tumor types harboring mutations in IDH2 can have alternative mutations in IDH1, including central cartilaginous tumors, diffuse gliomas, cholangiocarcinomas and several hematologic malignancies, among others. However, to the best of our knowledge, IDH1 mutations have not been reported in SPCRP. Here, for the first time, we report a case of SPCRP with a pathogenic IDH1 R132C mutation diagnosed in a 73-year-old female, expanding the mutational spectrum for this tumor type and confirming the expected IDH1/IDH2 dichotomy seen across numerous other tumor types. Case details, differential diagnostic considerations and clinical implications are discussed.