Malignant juxtaglomerular cell tumor.

Juxtaglomerular cell tumors (JGCTs) are rare, typically benign neoplasms; only rare cases are clinically or histologically malignant. We herein report the histologic, immunophenotypic, and molecular features of a clinically unsuspected, diagnostically challenging case of malignant JGCT in a 23-year-old man. The diagnosis is confirmed with electron microscopy. The case is notable for its marked mitotic activity, which has not been previously reported in JGCTs, and novel finding of GATA3 immunohistochemical positivity.