The histologic outcomes of indeterminate thyroid nodules with rat sarcoma mutations: A case series.

Molecular testing is an adjunct test for thyroid fine needle aspirations with indeterminate diagnoses, with certain mutations showing a greater risk of malignancy (ROM). Rat sarcoma (RAS) point mutations are the most common alterations in indeterminate thyroid nodules. While they can have a high ROM, they are also found in benign disease. This study describes the histologic outcomes of indeterminate nodules with RAS mutations. Bethesda III and IV thyroid nodules with ThyroSeq results showing RAS mutations (NRAS, KRAS, and HRAS) were identified between November 1, 2018 and February 28, 2023. Baseline patient characteristics, ThyroSeq results, and surgical diagnoses were collected. We identified 18 nodules with RAS mutations from 17 patients. Fourteen were NRAS (isolated NRAS in 6; NRAS with other abnormalities [NRAS+] in 8); one was isolated KRAS; and three were HRAS with other abnormalities (HRAS+). NRAS Q16R was the most common amino acid change. Twelve cases had follow-up. Two were malignant, a minimally invasive follicular carcinoma (NRAS+) and a papillary thyroid carcinoma, follicular variant (HRAS+). Three were noninvasive follicular thyroid neoplasms with papillary-like nuclear features (NIFTP), 2 HRAS+ and 1 NRAS+. Four were follicular adenomas, one being atypical (3 NRAS+ and one isolated NRAS). One was an oncocytic adenoma (isolated NRAS). Two were nodular hyperplasias (isolated NRAS and NRAS+, respectively). Twenty-eight percent of our RAS-mutated nodules were malignant or NIFTP. All three HRAS-mutated nodules were malignant or NIFTP. The three isolated RAS mutations with follow up were benign (adenomas or nodular hyperplasia). These findings were in line with the literature.