Metastatic large-cell neuroendocrine carcinoma of the lung masquerading as a primary gallbladder carcinoma: A case report.

Gallbladder neuroendocrine carcinoma is rare, representing ~4% of all primary malignant gallbladder neoplasms. We report the case of a 75-year-old female who presented for radiologic restaging for lung adenocarcinoma diagnosed elsewhere, demonstrating a hypermetabolic gallbladder mass. With concern for a gallbladder primary, radical cholecystectomy followed. Gross showed a 2-cm polypoid fundic mass; microscopically, tumor cells were arranged in sheets, with organoid features and necrosis, variable cytoplasm, vesicular-granular chromatin, prominent nucleoli, frequent mitoses, and apoptotic figures. Immunohistochemically, synaptophysin, chromogranin, CK7, and TTF-1 were positive; Ki67 was 80%. The combined findings were diagnostic of large-cell neuroendocrine carcinoma. Further investigation including outside slide review with additional stains revealed the lung primary to be classified large-cell neuroendocrine carcinoma, thus the gallbladder tumor representing metastasis. Within 4 months, the patient expired with widespread metastases. To our knowledge, this is the first reported case of metastatic lung large-cell neuroendocrine carcinoma to gallbladder in the English literature.