INI1-Deficient Carcinoma of the Gallbladder.

SMARCB1/INI1 (integrase interactor 1) deficient undifferentiated carcinomas of the gastrointestinal tract are highly aggressive neoplasms with a poor clinical outcome. Due to their rarity, the clinicopathological characteristics and molecular profiles of these tumors remain incompletely understood. In this report, we describe the first documented undifferentiated carcinoma with INI1 deficiency that originated in the gallbladder. Histological examination revealed a tumor composed of sheets of dyscohesive cells exhibiting a rhabdoid morphology. Immunohistochemical analysis confirmed the diagnosis of carcinoma with complete loss of INI1 expression. The diagnosis of INI1-deficient undifferentiated carcinoma can be challenging, and correlation of clinical findings, in conjunction with comprehensive immunohistochemical and molecular investigations, is crucial to establish the correct diagnosis and exclude potential mimicking entities.