SUN-383 - Considering Hemithyroidectomy for Management of Sporadic Medullary Thyroid Cancer: A Retrospective Review

Introduction: Medullary thyroid cancer (MTC) is a rare form of thyroid cancer, comprising 1-2% of thyroid cancer cases diagnosed in the United States. Approximately 75% of MTC is sporadic (non-hereditary). Though the majority of sporadic MTC is thought to be unicentric and unilateral, thyroid cancer management guidelines recommend total thyroidectomy for the treatment of all forms of MTC. There is emerging discussion in the literature regarding if hemithyroidectomy could be utilized to effectively treat sporadic MTC to reduce surgical risk and potentially obviate the need for lifelong thyroid hormone replacement.

Objective: To conduct a retrospective review of patients diagnosed with sporadic MTC and review surgical pathology reports to assess if hemithyroidectomy may be an effective surgical treatment and reasonable alternative to complete thyroidectomy for select patients.

Methods: A retrospective review was conducted of patients treated at a single tertiary care center diagnosed with MTC in the last 25 years, confirmed to be RET mutation germline negative, and who underwent total thyroidectomy (or hemithyroidectomy followed by completion thyroidectomy) with or without lymph node dissection. Chart review and data abstraction including review of surgical pathology reports was performed.

Results: 98 patients with a documented diagnosis of MTC were identified and 45 of those patients met the study inclusion criteria. The study population was 57.8% female and predominantly white (80%) with an average age at diagnosis of 51.2 years. The median pre-operative calcitonin level was 1498.5 pg/mL. Review of surgical pathology reports revealed that MTC was confined to a single lobe in 88.9% of patients (32 with unifocal disease and 8 with multifocal disease involving a single lobe +/- isthmus). Five (11.1%) patients had MTC involving bilateral thyroid lobes. Extrathyroidal extension and lymph node involvement were identified in all cases of bilateral MTC, though tumor sizes varied significantly from 1.5 to 5.2 cm. The average primary tumor size in the entire study population was 2.9 cm (SD 1.6 cm). RET gene mutations were identified in 11 of 16 tumors that were sampled. Notably, papillary thyroid cancer (PTC) was identified incidentally in 10 of the patients (22.2%), with 4 cases involving the thyroid lobe contralateral to the MTC.

Conclusions: This study corroborates that MTC is confined to a single thyroid lobe in a large majority of patients with non-hereditary disease, suggesting hemithyroidectomy may be a reasonable treatment option in select patients. More research is required to determine which factors may indicate or confer a higher risk of bilateral disease. Additionally, the rate of incidentally found PTC was relatively high in this study population, though the clinical relevance of this is not clear as the majority of the tumors discovered were microPTC.

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