Abstract
Medullary thyroid cancer is the neuroendocrine tumor (NET) of thyroid with mostly both secreting calcitonin and immunohistochemically showing calcitonin positivity. Occasionally; NETs of thyroid may have little or no calcitonin expression. We present a case of serum calcitonin negative and immunohistochemically calcitonin-negative staining tumor with positive reaction to neuroendocrine markers synaptophysin and chromogranin-A. The patient's right vocal cord was paralytic and thyroid mass was huge with descending to thorax till hilar region. We discussed diagnostic difficulties and way of treatment about NETs of thyroid with the light of current literature with this case.