A Comparison of the Predictive Value of International Medullary Thyroid Carcinoma Grading System (IMTCGS) With That of Other Risk Factors in a Chinese Medullary Thyroid Carcinoma Cohort.

Background: The International Medullary Thyroid Carcinoma Grading System (IMTCGS) was recently introduced in medullary thyroid carcinoma (MTC). This study aimed to assess the predictive value of the IMTCGS for disease response and survival, and compare its predictive ability with that of other traditional risk factors in a Chinese MTC cohort.

Methods: The data of 137 MTC patients undergoing initial surgery between January 2004 and June 2023 were included for analysis. Histologic features were reviewed by two pathologists. Kaplan-Meier survival analysis and Cox proportional hazard model were performed to analyse the association between risk factors (including IMTCGS high vs low grade) and progression-free survival (PFS) and disease-specific survival (DSS). ROC analysis and Delong's test were used to compare the predictive ability of IMTCGS with that of other risk factors.

Results: Local recurrence, distant metastasis, and disease-specific death were observed in 14/134 (10.45%), 3/134 (2.24%), and 6/137 (4.38%) MTC patients, respectively. IMTCGS, TNM stage, postoperative calcitonin, postoperative CEA, and vascular invasion were associated with PFS in Kaplan-Meier survival analysis (all p < 0.05). Postoperative calcitonin was the only independent predictor for PFS in multivariate analysis (HR = 1.002, p = 0.002). ROC analysis and Delong's test showed that postoperative calcitonin had superior predictive value for structural recurrence than IMTCGS (AUC 0.90 vs. 0.64, p = 0.002). IMTCGS, TNM stage, and vascular invasion were associated with DSS in Kaplan-Meier survival analysis (both p < 0.05). In multivariate analysis, IMTCGS was the only independent predictor for DSS (HR = 11.23, p = 0.05). The AUC of IMTCGS was 0.81 (p = 0.01) for disease-specific death.

Conclusion: In this Chinese MTC cohort, IMTCGS was a powerful predictor of disease-specific death, while postoperative calcitonin was a powerful predictor of structural recurrence.