MON-444 The Case of a Rare Anaplastic Thyroid Cancer Variant with Rhabdoid Features

Introduction: We present a very rare case of a variant of anaplastic carcinoma, a high-grade thyroid carcinoma with rhabdoid features. Less than 15 cases have been reported in English literature over the last 20 years. The prognosis of thyroid cancer with this variant phenotype is unfortunately very poor with a mean survival time of only 6 months after diagnosis. Treatment includes surgery, often a total thyroidectomy due to the rapid rate of growth of this tumor type. The benefits of chemotherapy and radiation are not yet apparent. Case presentation: A 49 year old female with history of breast cancer status-post recent chemoradiation therapy presented to the emergency department for a rapidly enlarging, right-sided neck mass. The mass had been present for approximately one month, but it was estimated to have grown from 3cm to 5cm within the two weeks prior. The patient was being followed by her ENT specialist and had a recent outpatient CT scan done. The results of the CT revealed a large thyroid tumor partially obstructing the esophagus and given the rapid progression of symptoms, she was instructed to go straight to the ED for emergent admission. Upon arrival, the patient reported not having consumed any solids or liquids for the past day due to concerns of aspiration and increasing neck pain. She had complaints of worsening dysphagia. Initial lab work revealed low thyroglobulin (1.4 ng/mL), elevated T4 (15.42 nmol/L) presumably due to Tamoxifen exposure, and elevated PTH (96.9 pg/mL), likely primary hyperparathyroidism. She was admitted and endocrine was consulted for further evaluation. The patient underwent a fine-needle aspiration biopsy showing high-grade anaplastic carcinoma with extensive necrosis and rhabdoid features. The tumor was eventually classified as stage 4B with gross extra thyroidal extension to the adventitial layers of the esophagus, thus it was determined to be unresectable. It was recommended at that time she have a percutaneous tracheostomy and feeding tube to protect her airway. However, the patient requested to be discharged so that she could obtain a second opinion regarding treatment options and prognosis. She subsequently underwent a total thyroidectomy at another hospital. Conclusion: It remains unclear whether this patient’s history of breast cancer treated with chemoradiation therapy played a role in the development of this rare thyroid carcinoma. Some cases of the rhabdoid phenotype are documented to have transformed from papillary thyroid carcinoma, for which radiation therapy is a well-known risk factor. Future studies should use molecular markers, such as BRAF V600E mutations common to papillary and anaplastic thyroid carcinomas, to help differentiate between types of thyroid cancers and avoid delayed treatment options for rapidly metastasizing thyroid tumors.