The value of the immunohistochemistry in a case of gastric neuroendocrine tumor and thyroid metastasis.

Thyroid metastasis is atypical. We present a 70-year-old female case that was first diagnosed as gastric cancer after surgical approach. Two years later a thyroidectomy was performed and the immunohistochemistry (IHC) profile revealed a neuroendocrine tumor (NET): poorly differentiated neuroendocrine carcinoma (with small cells), with positive reaction for SYN, CROMO, negative for calcitonin, TTF1 and thyreoglobulin. The Ki-67 index was 25%. Considering the unusual metastasis, the IHC exam of the stomach tumor was performed pointing the same features as the thyroid findings. This proved that the thyroid tumor was a metastasis from a primary gastric neoplasia. This is an unusual case of NET because of the thyroid involvement. Nevertheless, the IHC exam played the major role in elucidating the diagnosis and the prognosis of the case.