Introduction
Neuroendocrine neoplasms (NEN) often occur in the pancreas (P-NEN) and gastrointestinal tract (GINEN) [1]. Gallbladder (GB) NEN is rare and accounts for only 0.5% of all NEN and 2% of all gallbladder tumors [2]. Furthermore, patients with GB-NEC have poor prognosis [3]. Currently, there are no diagnostic imaging findings for GB-NEC. For NEC, a platinum-based regimen is commonly used, but there is only one report suggesting effectiveness of nivolumab [4]. Here, we report a case involving successful treatment of GB-NEC with nivolumab.