SUN-611 A Rare and Interesting Case of Primary Thyroid Lesion as Anaplastic Cancer and Lymph Node Metastasis with Papillary Thyroid Cancer

Background: Anaplastic thyroid cancers are very rare accounting for 1-2% of thyroid cancer. It has been hypothesized that it may start from one of differentiated thyroid cancer up to 30% of cases but usually there will be evidence of differentiated thyroid cancer like PTC in thyroid. Here, we present a rare case of anaplastic thyroid carcinoma on thyroid gland with cervical lymph nodes also positive for papillary thyroid cancer with no evidence of PTC in thyroid gland. Clinical case: 54-year female with h/o primary hypothyroidism and thyroid mass for several years presented to ER with complaints of neck pain where CT scan showed large right thyroid mass with tracheal compression. She had noticed rapid growth of mass for last 1-2 months with some compressive symptom like neck pain and dysphagia. Later, FNA of right thyroid Mass showed atypical lymphoid cells in a background of Hashimoto's thyroiditis. PET scan showed Intense FDG uptake in right thyroid lobe, right supraclavicular LN and right level 2LN. Core biopsy of thyroid was performed which showed poorly differentiated neoplasm with spindle morphology and Immunohistochemistry result favor a thyroid undifferentiated neoplasm. She underwent Total thyroidectomy with neck dissection and final pathology showed large, 8 cm, anaplastic thyroid carcinoma with invasion into the strap muscle. 12/85 LN were positive for cancer among them 10 were PTC and 3 were anaplastic carcinoma. Due to large primary tumor being anaplastic it was decided against radioactive ablation and she was referred for external beam radiation. Thyroglobulin level was 2.8 (2.8 to 40.9 ng/ml) after 11 days from surgery with TSH 2.32 (0.35 - 3.74 iu/ml) and undetectable anti thyroglobulin antibody. She tolerated radiation treatment well and repeat Tg level had decreased to 0.1 ng/ml when checked 4 months after surgery with suppressed TSH. Conclusion: Anaplastic thyroid cancers are very aggressive, undifferentiated cancers with almost 100% fatality within 1 years. It is more common in female and occurs mostly after age 60 to 65. It is usually presented with rapidly enlarging mass. There can be h/o prior differentiated thyroid. Our case did not have evidence of primary PTC with in thyroid but at least 10/ 85 removed lymph nodes were positive for PTC which is unusual. Our case is rare and unusual due coexistence of PTC in LN without primary PTC and with large anaplastic tumor in thyroid. This case also teaches us if there is rapid growth of existence thyroid mass, we should watch for possible anaplastic thyroid cancer and should not delay biopsy.