Pilomatrix carcinoma-like gallbladder carcinoma

Pilomatrix carcinoma (PC) is a malignant cutaneous tumor characterized by ghost cell keratinization, nuclear positivity for β-catenin, and mutations in catenin beta 1 (CTNNB1) exon 3. We report the first documented case of a primary gallbladder tumor exhibiting a PC-like phenotype with a CTNNB1 exon 3 mutation. The patient was a 74-year-old female who presented with a rapidly enlarging hepatic tumor. The tumor did not respond to preoperative chemotherapy but was removed with surgery. Histopathological examination of resection specimens revealed neoplastic cells forming solid nests of varying sizes, accompanied by ghost cell keratinization and necrosis. Immunohistochemical analysis demonstrated diffusely aberrant nuclear and cytoplasmic β-catenin staining. Molecular testing revealed a CTNNB1 exon 3 mutation. These findings were consistent with a PC-like phenotype. The patient was unresponsive to postoperative chemotherapy and developed pulmonary metastases, leading to death four months after surgery. The tumor is notable for its rapid progression and poor prognosis, highlighting the clinical significance of recognizing this rare histological subtype. To our knowledge, this is the first reported case of a gallbladder neoplasm exhibiting the full spectrum of histopathological and molecular features characteristic of PC, including the CTNNB1 exon 3 mutation.