Aberrant GATA3 reactivity in a clear cell renal cell carcinoma with clear cell papillary renal cell tumor-like features: a case report.

Clear cell papillary renal cell tumor (CCPRCT) has been reclassified from "carcinoma" to "tumor" in the latest World Health Organization (WHO) Classification in 2022 to better reflect its excellent outcome. Therefore, its distinction from its closest mimic, clear cell renal cell carcinoma (CCRCC), is now more clinically relevant than ever. The well-documented occurrence of tumors with significant overlapping morphologic and immunohistochemical features between CCPRCT and CCRCC has sparked a search for additional immunohistochemical markers that may aid in this distinction. Based on the putative distal nephron origin of CCPRCT, GATA binding protein 3 (GATA3) has been proposed as a sensitive and specific marker for this diagnosis, with only exceptional cases of CCRCC reported to show GATA3 reactivity. To the best of our knowledge, this is the first report of a molecularly-confirmed, low-stage, low-grade CCRCC showing overlapping histology with CCPRCT and an exceptional CCPRCT-like immunohistochemical profile, including diffuse nuclear expression of GATA3.