The application of a recently proposed 2-tier grading system for patients with medullary thyroid carcinoma (MTC) showed statistically significant differences in overall survival between the 2 groups, according to a study published in the Annals of Diagnostic Pathology.

Overall survival time for patients in the low-grade MTC group was significantly higher than that of patients in the high-grade group (P <.0001) using Kaplan-Meier analysis. Both univariate and multivariate analyses also showed that grade was associated with survival (P <.001 and P <.01, respectively). Grade was still associated with survival even after controlling for demographic variables, tumor size, and lymph node involvement (P =.025).

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“We applied the two-tier GS for MTC to our cohort of cases and found statistically significant differences in the overall survival among the two groups. Adding the grading to the pathology report communicates additional information regarding risk stratification in MTC,” the authors said.

Univariate analysis with Fisher’s exact test found that patients in the high-grade group were more likely to have vascular invasion (VI; P =.017) and distant metastasis (P <.0001) than the low-grade group.

Tumor necrosis, one of the criteria for classification into the high-grade group, was also associated with poor survival (hazard ratio [HR] 14.3; P =.00056) using univariate Cox regression. It remained associated with poor survival (HR 11.1; P =.008) in multivariate regression even after controlling for demographic factors including age and sex.

Cases with lymph node metastasis showed a significant correlation with age, VI, extrathyroidal extension, nuclear polymorphism, fibrosis, and distant metastasis using univariate analysis. Using multivariate Cox regression showed that VI, nuclear polymorphism, fibrosis, and distant metastasis remained significantly correlated.

Patients in the study were separated into either low-grade or high-grade MTC based on morphological criteria. Patients were categorized as high-grade if they had mitosis ≥5 per 2mm2 or the presence of necrosis.

A total of 59 MTC cases were included in the study with 52 (88%) being categorized as low-grade and the remaining 7 (12%) were categorized as high-grade. The mean age of the patients in the study was 58 years and the majority of cases (n=37; 64%) showed unifocal disease while the remaining 36% showed multifocality.


Podany P, Meiklejohn K, Garritano J, et al. Grading system for medullary thyroid carcinoma; an institutional experience. Ann Diagn Pathol. Published online February 1, 2023. doi:10.1016/j.anndiagpath.2023.152112