Neuroendocrine tumor presenting as metastatic carcinoid and later as insulinoma: a rare metamorphosis

We describe a very rare case of a neuroendocrine tumor, which initially presented as metastatic carcinoid with lesions in the liver and bones. Diagnosis was made by an elevated blood serotonin level and 24 hour urine 5HIAA. Liver biopsy confirmed the presence of a well differentiated neuroendocrine tumor (NET) staining positive for Chromogranin and negative for insulin. Two years after the initial diagnosis, the patient started to experience neuroglycopenic symptoms. Insulin and C-peptide levels were markedly elevated along with severe and recurrent hypoglycemic episodes. Due to extremely high insulin secretion from a large tumor burden, the patient’s clinical condition rapidly deteriorated in spite of maximal medical treatment. Shortly after the diagnosis of metastatic Insulinoma with unknown primary was made, the patient developed multiple organ system failure which limited invasive diagnostic techniques for localization. It appears that this patient’s neuroendocrine tumor had undergone a partial or complete change in its humoral function from a carcinoid or indolent neuroendcorine tumor to an Insulinoma or that the tumor started to co-secrete insulin along with serotonin. Less likely, he may have developed a separate tumor in the pancreas which was unable to be visualized by conventional imaging. Excess secretion of both Serotonin and Insulin from a single tumor is extremely rare and very few cases have been reported in the literature where a gastroenteopancreatic NET was found to secrete both insulin and serotonin.