Molecular testing is increasingly used in the assessment of thyroid nodules. Tumors harboring the same genomic variant may not behave the same because a gene variant is not expressed equally in tumor cells among patients. This study is to delineate interpatient variabilities in genomic variants in thyroid tumors and assess their diagnostic significance in definitive thyroid cancer diagnosis.

Interpatient differences in BRAF V600E, TERT promoter, and RAS variants (ie, NRAS, HRAS, and KRAS) were analyzed in residual thyroid fine-needle aspiration (FNA) biopsies and compared with surgical histopathologic diagnoses. Malignancy rates, sensitivity, specificity, positive predictive values (PPV), and negative predictive values (NPV) were calculated.

This retrospective study enrolled 620 patients (470 [75.8%] female; mean [SD] age, 50.7 [15.9] years), including 438 surgically resected thyroid tumors and 249 thyroid nodule FNA biopsies. Of 438 tumors, 178 (40.6%) and 58 (13.2%) carcinomas were detected with interpatient variabilities of BRAF V600E and TERT promoter variants (C228T and C250T), with variant allele fraction (VAF) levels ranging from 0.03% to 48.56% and 0.13% to 54.74%, respectively. Furthermore, 89 (20.3%) were identified with the presence of RAS variants, including 51 (11.6%) with NRAS, 29 (6.6%) with HRAS, and 9 (2.1%) with KRAS, with VAF levels ranging from 0.15% to 51.53%. VAF assays of 249 residual FNA specimens identified 50 specimens (20.1%) with BRAF V600E, 25 FNAs (10.0%) with TERT promoter variants, and 36 specimens (14.5%) with RAS variants with interpatient variabilities (including 23 FNAs [9.2%] with NRAS, 10 FNAs [4.0%] with HRAS, and 3 FNAs [1.2%] with KRAS). Interpatient differences in the 5 gene variants (NRAS, HRAS, KRAS, BRAF, and TERT) were detected in 54 of 126 indeterminate FNAs (42.9%) and 18 of 76 ND FNAs (23.7%). Compared with the 5 gene variants detected in the matched surgical specimens, VAF assays on residual FNA biopsies exhibited a high agreement (κ = 0.80; P < .001) and demonstrated a sensitivity of 87.1% (95% CI, 69.2%-95.8%), specificity of 92.5% (95% CI, 78.5%-98.0%), PPV of 90.0% (95% CI, 72.3%-97.4%), and NPV of 90.2% (95% CI, 75.9%-96.8%).

This diagnostic study delineated that quantitative discrimination of interpatient variabilities in genomic variants could facilitate cytology examinations in preoperative precision malignancy diagnosis among patients with thyroid nodules.