Insulin-secreting Large Cell Neuroendocrine Carcinoma of Pancreas Mimicking Primary Breast Carcinoma.

Functioning pancreatic neuroendocrine carcinoma (pNEC) is relatively less common. Here, we report a middle-aged lady, initially diagnosed as primary ductal carcinoma of the breast with multiple metastases, who was managed with excision biopsy of the breast tumor and palliative chemotherapy elsewhere. She later developed recurrent episodes of hypoglycemia following chemotherapy and was found to have hyperinsulinemic hypoglycemia, clearly suggestive of insulinoma. Ga-68 DOTANOC PET-CT scan showed DOTA-avid primary lesion in pancreas with intense uptake in several sites, including liver, bilateral adnexa, and intra-abdominal lymph nodes, favoring a probable functioning pancreatic neuroendocrine tumor (pNET) with distant metastases. Histopathology of her breast lesion was then re-examined, which showed features of neuroendocrine carcinoma (NEC) that was confirmed with immunohistochemistry (IHC), thus establishing the diagnosis of functioning pNEC. She was treated conservatively with octreotide and diazoxide for recurrent and refractory level 2 and 3 hypoglycemia. She was later discharged at her request on octreotide in a relatively stable condition, but died a week later. Despite being rare, diagnosing insulin-secreting pNEC is quite challenging. However, the diagnosis can be established based on radiological clues, somatostatin receptor expression based on functional imaging, and careful histopathological examination with appropriate IHC.