SAT508 Siblings With Heterozygous DICER1 c.322C>T, pGln108* Variant: A Novel Genetic Variant for DICER1 Syndrome

Disclosure: N.L. Yamashita: None. J. Austin: Consulting Fee; Self; Ascendis, Vertice. Research Investigator; Self; IBSA Pharmaceuticals. Background: Several genetic variants are implicated in DICER1 syndrome - a neoplasm predisposition syndrome with a spectrum of presentations with both benign and malignant tumors. DICER1 c.322C>T, pGln108* variant is a new mutation that was found in this case of two siblings presenting with thyroid cancers. Clinical case: Sibling A is a 10-year-old female who presented to the emergency department (ED) with a rapidly progressing right neck mass. She underwent fine needle aspiration (FNA) that returned as Follicular Lesion of Undetermined Significance (FLUS), Bethesda III. Subsequently, she had a right lobectomy, and pathology results revealed multiple follicular adenomatous nodules with focal papillary hyperplasia. Approximately one year later, she re-presented with a new left sided neck swelling with ultrasound revealing three new nodules. She underwent left lobectomy and pathology showed follicular variant papillary thyroid carcinoma (FVPTC). She was started on levothyroxine replacement daily. Her surveillance regimen included I-123 thyroid uptake scans which showed uptake in the neck. Her TSH-stimulated thyroglobulin was as high as 4.3 ng/mL with negative thyroglobulin antibody titer. She did not receive radioactive iodine ablation (RAI). Since then, routine thyroglobulin levels have remained low and neck ultrasounds have been reassuring. She is currently 19 years old. Approximately three years after Sibling A’s second lobectomy, her sister, Sibling B, presented as an 11-year-old female to the ED with neck swelling. Thyroid ultrasound showed multiple solid and cystic nodules on both right and left thyroid lobes. FNA returned with Bethesda Category IV (suspicious for follicular neoplasm) on the left lower nodule and Bethesda II (benign follicular nodule) on other nodules. She underwent total thyroidectomy and was found to have follicular thyroid carcinoma (FTC). TSH-stimulated thyroglobulin was as high as 8.9 ng/mL. Her surveillance thyroid scan showed uptake in the right thyroidectomy bed and 1.6 cm nodule was found on ultrasound. FNA of this lesion was benign with stable repeat thyroid scans with downtrending TSH-stimulated thyroglobulin. This patient is currently 15 years old. Soon after the Sibling B was diagnosed with FTC, the decision was made to pursue genetic analysis. Both siblings underwent mutation analysis which were both positive for heterozygous DICER1 c.322C>T, pGln108* variant.Conclusion: This case introduces a novel variant to DICER1 syndrome: DICER1 c.322C>T, pGln108* variant. Without a family history of multinodular goiter (MNG), thyroid cancers, or other associated tumors to this syndrome, these siblings had unusual presentations of a germline DICER1 syndrome variant. This case highlights the expressive variability in DICER1 syndrome and this variant may be of consideration when children present without other predisposing tumors. Presentation Date: Saturday, June 17, 2023