High RAS Allele Frequency Signals Increased Risk of TERT Promoter Mutations in Thyroid Tumors

RAS mutations are among the most common genetic alterations in thyroid cancer and are generally associated with less aggressive behavior. However, when co-occurring with TERT (telomerase reverse transcriptase) promoter mutations, known markers of poor prognosis, tumors exhibit markedly more aggressive features. The allele frequency (AF) of RAS may serve as a potential indicator of clonal dominance and the likelihood of additional high-risk mutations, such as TERT mutation. This study aims to assess whether a high RAS AF correlates with the presence of coexisting TERT promoter mutations and other molecular alterations.

A retrospective chart review was performed on 111 patients with thyroid nodules harboring RAS mutations, either alone or in combination with TERT promoter mutations. All patients underwent molecular testing with ThyroSeq v3 and subsequent thyroidectomy at McGill University teaching hospitals. RAS AF was analyzed in relation to TERT mutation status, nodule size, and other molecular alterations including copy number alterations (CNA) and gene expression profiles (GEP).

The mean RAS AF was significantly higher in nodules with both RAS and TERT mutations (38.1%) compared to those with RAS mutations alone (22.1%) (p = 0.002). Nodules with coexisting TERT mutations were also significantly larger (mean size: 3.7 cm vs. 2.4 cm; p = 0.005). Malignant nodules, regardless of TERT status, showed a trend toward higher RAS AF than benign nodules (23.0% vs. 16.3%; p = 0.052). Higher RAS AF was also associated with the presence of CNA and/or GEP positivity. Notably, GEP was positive in 100% of nodules with both RAS and TERT mutations, compared to 37.5% in RAS-only nodules (p = 0.002).

A high RAS AF increases the likelihood of a TERT promoter mutation and other genetic alterations, highlighting the importance of RAS AF in optimizing patient care and management.