BACKGROUND
Medullary thyroid carcinoma (MTC) is a rare thyroid cancer that originates from cells called parafollicular C-cells in the thyroid that produce a hormone called calcitonin.

Calcitonin plays a minor role in the regulation of the body’s calcium levels. In the setting of MTC, calcitonin serves as a cancer marker, since the cancer cells continue to secrete calcitonin. MTC can frequently run in families (familial MTC) as well as occurring in patients without a family history (sporadic MTC).

Once MTC is diagnosed, a total thyroidectomy is generally recommended for patients, but the extent of surgery regarding lymph node dissection remains uncertain. Further, there is debate about the extent of surgery in the neck in patients who do not have known spread of the cancer outside of the thyroid prior to surgery. Finally, a total thyroidectomy is associated with a higher rate of surgical complications, and thyroid lobectomy has become increasingly advocated for other types of thyroid cancer if there is no evidence of spread of the cancer to the opposite lobe. It is unclear whether this approach would be appropriate for treatment of MTC.

This study investigated frequency of finding small foci of MTC in the lobe opposite to the lobe containing the primary cancer that was not identified on ultrasound before surgery (occult foci). The authors also compared the finding of occult foci between patients with sporadic MTC and those with familial MTC.

THE FULL ARTICLE TITLE
Mao YV et al. Extent of surgery for medullary thyroid cancer and prevalence of occult contralateral foci. JAMA Otolaryngol Head Neck Surg 2024;150(9):838; doi: 10.1001/jamaoto.2023.4376. PMID: 38270925.

SUMMARY OF THE STUDY
This study included a group of patients who underwent thyroidectomy for MTC in academic medical centers from September 1998 to April 2022. The study group was composed of 176 patients with an average age at diagnosis of 55 years (range, 2–87; 57.6% female). In the whole group, 46 (26.0%) had MTC in the opposite lobe and in 9 of these patients (5.1%), the MTC was not identified on preoperative ultrasound. Among 109 patients who underwent genetic testing, 38 (34.9%) had MTC in the opposite lobe and in 8 (7.3%), the MTC was not seen on ultrasound. Occult foci were found in 4 of 30 (13.3%) patients with familial MTC as compared to 4 of 79 (5.0%) patients with sporadic MTC. The risk of having occult foci in familial MTC was 4.3% while the risk in patient with sporadic MTC was 3.4%. There were 12 of 176 (6.8%) patients who underwent initial lobectomy, 5 of whom had undetectable calcitonin concentration. Of these, 4 patients underwent completion thyroidectomy, none of whom were found to have occult of MTC in the remaining lobe.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
This study shows that thyroid lobectomy could be considered in patients with sporadic MTC and no ultrasonography findings in the opposite lobe. While there continues to be a slightly higher risk of occult MTC in the opposite lobe in patients with familial MTC, the risk continues to be low and lobectomy could be considered in this group as well. Finally, an undetectable calcitonin level post-op continues to be an excellent indicator of no significant remaining MTC even in the setting of a lobectomy.

— Alan P. Farwell MD

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