Outcomes of TSHR Mutations in Indeterminate Thyroid Nodules

• TSHR mutations are rare and understudied in indeterminate thyroid nodules • TSHR mutations predict autonomous thyroid function and lower TSH levels • Isolated TSHR mutations were benign regardless of allele frequency • Malignancy occurred only with additional oncogenic alterations • Findings refine molecular risk stratification and patient counseling The thyrotropin receptor (TSHR) mutation can be present in autonomously functioning thyroid nodules (AFTNs). Our objective was to evaluate whether patients with a TSHR mutation developed AFTNs and to assess the impact of this mutation on thyroid malignancy. We conducted a multicenter retrospective study of 1211 patients from Montreal, Canada, and from Tel Aviv, Israel, who underwent molecular testing (ThyroseqV3®) from January 2018 to December 2022 following an indeterminate cytology result (Bethesda III-IV). All TSHR-positive patients (n=56) and 90 randomly selected mutation-negative patients were included. TSH levels were measured at least twice over 1–3 years following molecular testing. The case group was predominantly female (94.8%) with a mean age of 51.2 years. The mean TSH levels in the control and case groups were 2.29 (CI=95% 1.93–2.66) and 1.55 (CI=95% 1.23–1.86) at first follow-up, and 2.17 (CI=95% 1.80–2.54) and 1.33 (CI=95% 1.01–1.66) at second follow-up. Higher allele frequency correlated with lower TSH levels (P=0.005, P=0.002). All isolated TSHR mutations were associated with benignity regardless of allele frequency, while co-occurring genetic alterations were associated with malignant outcomes. TSHR mutations are generally benign and correlate with lower TSH levels. Co-mutations may influence thyroid function and malignancy risk.