Diagnostic utility of RAS mutation testing for refining cytologically indeterminate thyroid nodules.

RAS mutations are prevalent in indeterminate thyroid nodules, but their association with malignancy risk and utility for diagnosis remains unclear. We performed a systematic review and meta-analysis to establish the clinical value of RAS mutation testing for cytologically indeterminate thyroid nodules. PubMed and Embase were systematically searched for relevant studies. Thirty studies comprising 13,328 nodules met the inclusion criteria. Random effects meta-analysis synthesized pooled estimates of RAS mutation rates, risk of malignancy with RAS positivity, and histologic subtype outcomes. The pooled mutation rate was 31 % (95 % CI 19-44 %) among 5,307 indeterminate nodules. NRAS mutations predominated at 67 % compared to HRAS (24 %) and KRAS (12 %). The malignancy rate with RAS mutations was 58 % (95 %CI=48-68 %). RAS positivity increased malignancy risk 1.7-fold (RR 1.68, 95 %CI=1.21-2.34, p=0.002), with significant between-study heterogeneity (I2=89 %). Excluding one outlier study increased the relative risk to 1.75 (95 %CI=1.54-1.98) and I2 to 14 %. Funnel plot asymmetry and Egger's test (p=0.03) indicated potential publication bias. Among RAS-positive malignant nodules, 38.6 % were follicular variant papillary carcinoma, 34.1 % classical variant, and 23.2 % follicular carcinoma. No statistically significant difference in the odds of harboring RAS mutation was found between subtypes. In conclusion, RAS mutation testing demonstrates clinical utility for refining the diagnosis of cytologically indeterminate thyroid nodules. Positivity confers a 1.7-fold increased malignancy risk, supporting use for personalized decision-making regarding surgery vs. monitoring. Follicular variant papillary carcinoma constitutes the most common RAS-positive malignant histological subtype. See also the graphical abstract(Fig. 1).