Researchers reported that a grading system developed for medullary thyroid carcinoma (MTC) has prognostic value and is reproducible and published their findings in Endocrine Pathology.

Medical researchers have recently focused on uncovering whether histological tumor grades of MTC correspond to prognosis in any way. Some researchers have started to develop new grading schemes for MTC based on factors such as mitotic count, the presence/absence of tumor necrosis, and the Ki-67 proliferative index.

The International Medullary Thyroid Carcinoma Grading System (IMTCGS) defines a high-grade tumor as one possessing at least 1 of the following features: a mitotic count ≥5 mitoses per 2 mm2, the presence of tumor necrosis, or a Ki-67 proliferative index ≥5%. Williams and colleagues focused on this particular grading system and attempted to study its interobserver reproducibility when assessing MTC grades.

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The research team recruited 44 sporadic MTC cases, which were then graded according to the IMTCGS criteria. A high-grade tumor was graded according to the criteria mentioned earlier; a low-grade tumor must have <5 mitoses per 2 mm2, a Ki-67 proliferative index <5, and no tumor necrosis. 

To study the reproducibility of assessed IMTCGS grades, the research team organized 3 groups to independently study the cohort of 44 cases recruited, recording the mitotic count, Ki-67 proliferative index, and the presence/absence of tumor necrosis.

“We found that there was a strong level of agreement for assigned IMTCGS grade among the three teams of graders,” they wrote. This confirms that the tumor grade as defined by the IMTCGS is indeed reproducible.

“We expect that IMTCGS grade will become an important component of pathology reports for MTC not only for prognostication, but also to identify patients who might benefit from shorter follow-up intervals and more extensive imaging for evaluation for metastases,” the researchers concluded.


Williams JF, Zhao M, Najdawi F, et al. Grading of medullary thyroid carcinoma: an interobserver reproducibility studyEndocr Pathol. Published online May 13, 2022. doi:10.1007/s12022-022-09718-0