ODP489 Insular Thyroid Cancer: A Rare Case of Undifferentiated Thyroid Carcinoma

INTRODUCTION: Insular thyroid cancer (ITC) is a rare form of thyroid cancer derived from follicular cells. ITC requires a histopathologic diagnosis and has an intermediate morphology between well differentiated thyroid cancers (follicular and papillary) and undifferentiated thyroid cancer (anaplastic). The rate of metastasis and mortality are higher compared with well-differentiated thyroid carcinomas. CASE PRESENTATION: A 74-year-old woman presented for a 1 year history of rapidly progressive neck mass associated with neck pain, limited neck motion, loss of appetite, weight loss, and dysphagia. Past medical history included hypertension, type 2 diabetes, dyslipidemia, and vitamin D deficiency. There was no history of neck radiation or family history of cancer. Physical examination revealed a 10×7 cm neck mass with cervical adenopathy. Vital signs were unremarkable. Laboratory studies showed TSH of 0.71 uIU/mL (0.270-4.200), free T4 of 0.57 ng/dL (0.93-1.70) and thyroglobulins of 213.616 ng/dL (1.6-59.9). Neck CT demonstrated a multilobulated mass in the left thyroid lobe measuring 12×5.2×5.6 cm with tracheal deviation, multiple nodules surrounding the carotids and bone metastasis. Fine needle aspiration showed a mixed pattern of thyroid follicles. An excisional biopsy showed nests and sheets of small uniform cells with scattered abortive follicles and mitosis consistent with ITC. There was no necrosis. The Ki67 index was 10-20%. On immunohistochemical analysis TTF1 and thyroglobulin were positive and P63, calcitonin, and PTH were negative. Tracheostomy and PEG tube placement were required due to mass obstructive effect. Radiation and steroids were initiated before starting lenvatinib. The patient was not a surgical candidate due to tumor extension to the carotids. She ultimately succumbed to the disease after a 45-day hospital course complicated by pneumonia. DISCUSSION: ITC is a rare type of thyroid tumor with a mortality rate of 12-75%. The diagnosis is based on histopathology, demonstrating solid nests (insulae) of small, uniform carcinoma cells, small follicles containing thyroglobulin, frequent necrotic foci and variable mitotic activity. The tumor cells in ITC are derived from poorly differentiated follicular cells expressing thyroglobulin. The immunostaining of thyroglobulin differentiates ITC from other poorly differentiated thyroid tumors. In this case the immunohistochemical analysis was positive for thyroglobulin and negative for calcitonin, which confirmed that the tumor cells were follicular in origin 1 . ITC behaves differently compared with other thyroid carcinomas, with more frequent metastasis and lower average 20-year post-diagnosis survival. Our patient had other characteristics that conferred a poor prognosis, including advanced age, high rate of mitosis, and multiple metastases. Although surgery and radioactive iodine are first line, this patient's tumor extension required alternative therapies. Radiotherapy and lenvatinib, a tyrosine kinase receptor inhibitor, were employed unsuccessfully. 1. Soza, J., et al. Insular Thyroid Cancer. Cancer, 3260-3267. Presentation: No date and time listed