SAT535 ANKRD26-RET Fusion Positive Metastatic Papillary Thyroid Carcinoma - Advanced Presentation of a Rare Mutation

Disclosure: H. Hashmi: None. A. Ankireddypalli: None. L. Burmeister: None. A. Nelson: None. K. Amin: None. Background: While rearranged during transfection (RET) protooncogene mutations have been commonly associated with thyroid malignancy, ankyrin repeat domain containing protein 26 (ANKRD26) has been primarily linked to hematologic malignancy. Exon 29 of ANKRD26 (Chromosome [Chr] 10p12.1) has been shown to fuse with exon 12 of RET (Chr 10q11.21), resulting in a genetic fusion mutation ANKRD26:RET. This is a rare genetic mutation in papillary thyroid cancer with only one previously reported case. We report the first case in the US of this novel genetic mutation with a unique clinical presentation. Clinical Presentation: A 48-year-old, male patient presented with lower back pain radiating to the lower extremities of one year duration. MRI lumbar spine revealed an irregular mass lesion in the L1 vertebral body with extraosseous soft tissue extension, L1 compression fracture and extension into the T12 body. CT CAP revealed a 4.8 x 3.6 cm, heterogenous right thyroid lobe with tracheal compression and sub centimeter pulmonary nodules in the left lower and right middle lobes. Biopsy of the L1 paravertebral mass was diagnostic for metastatic thyroid carcinoma of a follicular pattern. Molecular testing with a next generation sequencing fusion profile assay was positive for ANKRD26:RET gene rearrangement. Thyroid ultrasound was notable for a solid, hypoechoic, 3.2 x 3.1 x 2.9 cm right lobe nodule with echogenic foci and level 4 lymph nodes with loss of reniform shape and fatty hilum. FNA of the nodule and right level 4 lymph node was suspicious for follicular neoplasm. The patient was admitted for acute cord compression necessitating extensive laminectomy, vertebral reconstruction and resection of the L1 paraspinal tumor. Pathology was positive for metastatic, follicular variant, papillary thyroid carcinoma. Total thyroidectomy, central and right modified radical neck dissection was performed. Pathology demonstrated a 4.2 cm papillary carcinoma, follicular type with tall cell variant; confined to the thyroid. Extensive angioinvasion (≥ 4 vessels) and lymphatic invasion was present. 10/32 positive lymph nodes. TNM grading was T3aN1bM1. Summary: The only other case of ANKRD26-RET fusion positive papillary thyroid cancer in the literature was reported by Staubitz et al in Germany in 2019. They reported a case of a 78-year-old male with follicular variant papillary thyroid carcinoma (pT3,pN0,M0). To our knowledge, our case is the second worldwide and the first to be reported in the United States of this rare fusion protein positive thyroid cancer. Such an aggressive presentation with distant osseous metastases has to our knowledge not been previously described. Conclusion: The clinical and therapeutic implications of this rare genetic mutation are not currently well elucidated. We present this case with the intent to expand the existing literature and increase recognition of this rare genetic mutation. Presentation Date: Saturday, June 17, 2023