Validation of the International Medullary Thyroid Carcinoma Grading System in Patients with Distant Metastases
Authors' conclusion
The IMTCGS is a strong independent prognostic factor in patients with metastatic MTC. Patients with IMTCGS high-grade tumors and Ki-67 index ≥20% represent a high-risk subgroup with the poorest prognosis.
Study context
- Population
- Patients with metastatic medullary thyroid carcinoma (MTC) treated at Gustave Roussy 2000–2024, International Medullary Thyroid Carcinoma Grading System (IMTCGS) assessed on the primary tumor
- Participants
- 99 patients
- Exposure
- IMTCGS high-grade vs low-grade MTC
- High-graden = 67
- Low-graden = 32reference
- Outcome
- Median OS
Methodological detailsmonocentric
- Monocentric
Main finding
As reported in the abstract
P = 0.01
Observational data: associations, not effects.
Further findings
Time to systemic treatment initiation (TTI)
P < 0.001
OS from treatment initiation, patients who received systemic therapy (n = 75)
P = 0.865
| Outcome | HR | P value |
|---|---|---|
| OS by Ki-67 indexKi-67 ≥20% vs Ki-67 <5% | 6.11 | P < 0.001 |
| OS by Ki-67 indexKi-67 ≥20% vs Ki-67 5-19% | 3.29 | P = 0.001 |
- Overall survival (OS) by Ki-67 index: Ki-67 ≥20% 2.6 years
- OS by Ki-67 index: Ki-67 <5% 10.5 years
- OS by Ki-67 index: Ki-67 5-19% 6.5 years
Multivariable analysis of OS and TTI
- IMTCGS high-grade and bone metastases independently associated with shorter OS and TTI
- P < 0.05 for both
- RET-M918T mutation not associated with worse OS
Original publication
Validation of the International Medullary Thyroid Carcinoma Grading System in Patients with Distant Metastases. Thyroid. Published 23 October 2025. doi:10.
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