Invasive poorly cohesive carcinoma with focal signet ring cell features arising from intracholecystic papillary neoplasm in the gallbladder.

A woman in her 70s was referred to our hospital after screening abdominal ultrasonography revealed a 2-cm nodular lesion in the gallbladder. Contrast-enhanced computed tomography and endoscopic ultrasonography revealed multiple small polypoid lesions involving the fundus and body, and laparoscopic cholecystectomy was performed for diagnosis and treatment. Pathological examination demonstrated multifocal intracholecystic papillary neoplasm (ICPN) composed of prominent papillary epithelial proliferation and background flat low-grade biliary intraepithelial neoplasia. Within a 6-mm invasive focus, scattered discohesive carcinoma cells infiltrated to the subserosal layer; signet ring cell morphology was present only focally. Neuroendocrine markers were negative, arguing against goblet cell adenocarcinoma, and upper gastrointestinal endoscopy showed no evidence of gastric primary carcinoma. The ICPN, pyloric gland-like invasive component, and poorly cohesive carcinoma shared a predominantly gastric/pyloric immunophenotype with focal intestinal differentiation. Based on these findings, the lesion was diagnosed as ICPN with associated invasive poorly cohesive carcinoma with focal signet ring cell features. Previous ICPN-associated carcinomas with signet ring cells have been mucinous adenocarcinomas; in contrast, our case showed a small non-mucinous poorly cohesive invasive component. Thorough sampling is therefore essential in ICPN, because even a minute high-grade invasive focus may affect clinical management and prognosis.