BACKGROUND
Medullary thyroid cancer (MTC) is a relatively rare type of thyroid cancer. While it is the 3rd most common type of thyroid cancer, it only comprises ~3% of all cases of thyroid cancer. MTC arises from the parafollicular cells of the thyroid, also known as C cells, which are responsible for producing the hormone calcitonin. The standard treatment for this cancer is removing the thyroid completely (total thyroidectomy) as well as the lymph nodes in the lateral neck (bilateral neck dissection). This treatment is considered the most effective way to cure the disease when it has not spread.

After surgery, physicians monitor for MTC recurrence by measuring serum calcitonin levels and performing imaging, most often neck ultrasound. If the cancer has been completely removed, calcitonin levels should be very low or undetectable. Undetectable calcitonin levels with negative neck imaging is evidence of a cure of MTC. For patients who are not cured, calcitonin levels steadily increase over time. Indeed, studies show that the long-term prognosis of MTC, the prediction of the course of the disease and the effectiveness of treatment depends on the rate at which the calcitonin level doubles (called the calcitonin doubling time (CDT). When the CDT is longer than two (2) years, overall survival, recurrence-free survival, and distant metastasis- free survival are significantly better.

Determining the grade of a cancer is also essential for predicting the prognosis. Cancer’s grade reflects how abnormal the cancer cells appear when examined under a microscope compared to normal cells. Cancers with cells closely resembling normal healthy cells are categorized as low-grade, while those with more abnormal cells are classified as high-grade. Low-grade cancers are usually less aggressive and have a better prognosis. The International Medullary Thyroid Cancer System is a recent development that measures the grade of MTC and utilizes three different markers of cell division. High levels of these markers indicate a high-grade cancer.

This study aimed to investigate the differences in CDT between high and low-grade MTC. The authors hypothesized that high-grade cancers would have a faster CDT, leading to a worse clinical outcomes.

THE FULL ARTICLE TITLE
Nigam A et al 2022. Tumor grade predicts for calcitonin doubling times and disease-specific outcomes after resection of medullary thyroid carcinoma. Thyroid 32:1193–1200. PMID: 35950622.

SUMMARY OF THE STUDY
In this study, the authors investigated 117 patients who had undergone surgery for MTC between 1986 and 2017. Two pathologists evaluated the cancers and classified them as high or low grade based on the International Medullary Thyroid Cancer Scoring System. The patients’ serum calcitonin levels were measured before and after surgery, at 6 and 12 months post-surgery, and every 6 months after that.

The analysis revealed that cancer grade and CDT were powerful indicators of clinical outcomes. By the end of the study, 70.5% of patients with low-grade MTC remained cancer-free, whereas only 9.1% of high-grade MTC patients remained cancer-free. Additionally, 2.1% of low-grade MTC patients died, compared to 45.4% of high-grade MTC patients. Among the 95 patients with low-grade MTC, 6 (6.3%) had a CDT of 1-2 years, 23 (24%) had a CDT of 2 or more years, and 65 (68.4%) did not experience a doubling of calcitonin levels. But of the 22 patients with high-grade MTC, 16 (72.7%) had a CDT of 1 year or less, 4 (18.2%) had a CDT of 1-2 years, and only 1 patient did not experience a doubling of calcitonin levels. Thus, high-grade MTC patients had significantly faster CDT than low-grade MTC patients. Furthermore, patients with high-grade MTC and CDT of less than 2 years had the poorest overall survival and recurrence-free survival.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
Cancer grade and CDT can help predict prognosis in MTC. Most patients with high-grade MTC have a CDT of less than 2 years. This is why it is essential to frequently monitor calcitonin levels in MTC survivors since a rapid doubling of levels may predict cancer recurrence.

— Phillip Segal, MD

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