Abstract:【Abstract】 Objective To explore the clinicopathological features and differential diagnosis of the calcitonin negative neuroendocrine tumor of thyroid.Methods A case of calcitoninnegative neuroendocrine tumor of thyroid was diagnosed. Then, the history of a case of calcitoninnegative neuroendocrine tumor of thyroid was collected. The morphological examination and the immunophenotype detection of the tumor had been conducted. In addition, the relative references were reviewed.Results A 52yearold female patient underwent total thyroidectomy in our hospital, a gray and solid nodule, which is 0.6 cm in diameter, was found in the right lobe of thyroid, with blurred border and medium hardness. Under microscope, the tumor cells were composed of spindle cells or oval cells, with medium cytoplasm, small nuclear, coarse chromatin and unclear nucleoli. They arranged in nests with interstitial fibrous tissue proliferation. The immunophenotype examination indicated that TTF-1, CgA, Syn and CEA were all diffusely positive while TG and Calcitonin were negative.The index of Ki67 proliferation was less than 1%. Conclusion Calcitoninnegative neuroendocrine tumor in thyroid is a rare tumor. Its diagnosis should rely on the pathological morphology and especially, on the immunophenotype examination.