Extrapulmonary small cell: a novel case of small cell carcinoma of the thyroid gland

Neuroendocrine tumors comprise a large group of malignancies which share unique morphological features and are characterized by the presence of neuroendocrine markers such as synaptophysin, chromogranin-A, and CD56 (N-CAM), ranging from indolent tumors, such as carcinoid tumors, to aggressive tumors, such as small cell carcinoma. The lung is the most common site for primary neuroendocrine tumors. Extrapulmonary primary sites of small cell carcinoma are rare but have been documented arising from various sites including esophagus, stomach, colon and rectum, gallbladder, thymus, salivary gland, ovary, cervix, bladder, prostate, and skin. We present a case of small cell carcinoma arising from the thyroid gland, a site not previously described in the literature. A 59-year-old woman presented with a thyroid mass, which, after resection, showed small cell morphology and positive immunostains for TTF-1, synaptophysin, chromogranin-A, CD56, etc. Five months after diagnosis, she had widely metastatic disease. After a near-complete response to the first chemo-treatment, her disease progressed. Following local radiation and more rounds of chemotherapy, she succumbed to the disease, 15 months after diagnosis. Our patient had no pulmonary lesions at the time of diagnosis to suggest metastasis from the lung. Much like its pulmonary counterparts, this small cell carcinoma of primary thyroid origin displayed an aggressive clinical course and poor outcome. Although it shows early sensitivity to chemotherapy, small cell carcinoma remains a difficult-to-treat cancer with a poor prognosis and can rarely be seen originating in organs outside of the lung.