PTH and neuroendocrine neoplasm: Parathyroid carcinomas are neuroendocrine tumors and generally positive for chromogranin A. Other neuroendocrine tumors in the neck such as medullary thyroid carcinoma will also shows staining for chromogranin A, but medullary thyroid carcinomas are usually positive for thyroid transcription factor 1 while negative for parathyroid hormone.