Biphasic large cell neuroendocrine carcinoma - Pure mucinous carcinoma of the gallbladder (MANEC): A unique combination

Introduction. We report a case of primary combined large cell neuroendocrine carcinoma (LCNEC) - pure mucinous carcinoma of the gallbladder (MANEC) - which represents the first description of this entity. Methods. The patient is a 59-year-old Italian male who underwent cholecystectomy under a preoperative diagnosis of cholecystitis with gallstones and gallbladder tumour. During laparotomy, cholecystectomy, liver wedge resection and regional lymph node dissection were performed. The resected gallbladder showed a thickened wall, gallstones and a 4 cm gelatinous, cauliflowerlike soft tissue mass. Results. Following surgery, the gallbladder tumour was diagnosed as a mixed endocrine-exocrine carcinoma. There was evidence of lymph node metastasis or direct liver invasion. The mucin-producing carcinoma was composed of poorly differentiated glandular cells with mucin lakes. The LCNEC was characterized by large cells with prominent nucleoli, coarse chromatin and a high mitotic rate. The cells showed an "organoid" growth pattern with rosette formation and frequent areas of necrosis. Chromogranin A, synaptophysin and CD56 were diffusely and strongly expressed. Discussion. This case may provide helpful insights regarding the histogenesis of this unusual combination of tumors: the concept of a collision tumor between two neoplasms that have arisen in adjacent areas may be the best explanation for its pathogenesis.