Grading system for medullary thyroid carcinoma; an institutional experience.

Area of Science:

• Endocrinology
• Oncology
• Pathology

Background:

• Medullary thyroid carcinoma (MTC) is a rare but aggressive thyroid malignancy.
• A recently proposed two-tier grading system (GS) for MTC aims to improve risk stratification.
• The generalizability and application of this GS require validation in diverse patient cohorts.

Purpose of the Study:

• To evaluate the generalizability and application of a novel two-tier grading system for Medullary thyroid carcinoma (MTC).
• To assess the correlation between the proposed grading system and clinicopathological features and patient outcomes.

Main Methods:

• A cohort of 59 Medullary thyroid carcinoma (MTC) cases were retrospectively analyzed.
• Cases were assigned to either low-grade (LG) or high-grade (HG) categories based on mitotic count and necrosis.
• Morphologic criteria included mitosis (<5/2 mm² for LG, ≥5/2 mm² for HG) and presence of necrosis.

Main Results:

• Of 59 MTC cases, 88% were classified as LG and 12% as HG.
• High-grade (HG) MTC demonstrated significant associations with vascular invasion, distant metastasis, nuclear pleomorphism, and prominent nucleoli.
• Tumor grade and necrosis were significantly associated with overall survival (HR=22.7, p<0.01 and HR=11.1, p=0.008, respectively) after adjusting for demographics.

Conclusions:

• The application of the two-tier grading system to an MTC cohort revealed statistically significant differences in overall survival between low-grade and high-grade groups.
• Incorporating this grading system into pathology reports provides valuable prognostic information for risk stratification in Medullary thyroid carcinoma.
• The grading system enhances communication of risk beyond traditional staging.