Poorly differentiated "insular" carcinoma of the thyroid: a case report.

Poorly differentiated "insular" carcinoma of the thyroid is a rare type of thyroid malignancy, situated morphologically and biologically in an intermediate position between well-differentiated (papillary and follicular) and undifferentiated (anaplastic) carcinoma. Here we report a case of a 56-year-old woman who developed a mass over the left thyroid gland in 1988, and received a thyroid operation in 1990 which was reported as benign lesion. Three years later, a mass recurred over the right lobe of the thyroid, and another thyroid operation was performed. The pathological report was medullary carcinoma. Four months later, recurrent mass over the right thyroid bed developed. Fine-needle aspiration biopsy of the mass showed moderately high cellularity with moderate pleomorphism, and multinucleated giant cells. Distinct cytoplasmic blue granules were also found in Liu's stain. She received total thyroidectomy and right neck radical dissection. Pathology examination showed well-defined nests of tumor cells ('insulae'), and immunohistochemical study showed positive stain for calcitonin. Pathologic diagnosis was poorly differentiated "insular" carcinoma of the thyroid. Four months after operation, recurrent neck mass over the suprasternal notch developed. Computerized tomography of neck and chest showed tumor mass over left thyroid bed with extension to anterior mediastinum. Whole body 131I scan showed mediastinum involvement and multiple bony metastases. Ablative 131I treatments (150 mCi and 200 mCi) were given twice, but in vain. The patient died 14 months after her last operation.