Poorly Cohesive Cell Carcinoma of the Gallbladder with Signet Rings and Neuroendocrine-Like Morphology: A Rare Incidental Histopathological Diagnosis with Lessons to Learn.

<strong>BACKGROUND</strong> Poorly cohesive cell carcinoma of the gallbladder is extremely rare. <strong>CASE REPORT</strong> Here we present a case of a 46-year-old male with the clinical diagnosis of acute cholecystitis. The ultrasound showed gallbladder wall thickening and multiple stones. Cholecystectomy was performed, and the gross examination revealed linitis plastica-like thickening of the gallbladder wall. The microscopic examination revealed diffuse infiltration by a poorly differentiated tumor with signet rings. Another component with insular growth pattern and salt-and-pepper nuclei was present. Immunohistochemical findings were consistent with poorly cohesive cell carcinoma of the gallbladder. Imaging studies revealed regional lymph nodes involvement, in addition to peritoneal and liver metastases. The patient was given chemotherapy, and there was no evidence of disease progression at 4 months post-operation. <strong>CONCLUSIONS</strong> This case supported that all cholecystectomy specimens must be examined. In addition, although poorly cohesive cell carcinoma was reported to be aggressive, the present case showed a protracted clinical course; this pointed to the need for early clinicoradiological suspicion. This is the first case of poorly cohesive cell carcinoma of the gallbladder with a neuroendocrine-like morphology that mimics mixed adenoneuroendocrine carcinoma. Immunohistochemistry is invaluable in such a scenario.