BACKGROUND
Hürthle-cell cancer (HCC) is a rare type of thyroid cancer, representing 3-5% of all thyroid cancers. HCC used to be classified as a subtype of follicular cancer. However, in 2017, the World Health Organization (WHO) identified HCC as a different type, because of significant differences in the cancer behavior and prognosis. Overall, HCC has more aggressive features and a poorer prognosis than follicular thyroid carcinomas. Because of this, usual therapy includes a total thyroidectomy and many also undergo radioactive iodine therapy. More recently, in 2022, WHO recommended using the term “oncocytic carcinoma of the thyroid” instead of HCC. Prior studies of this type were small, given the rarity of HCC, and they reported conflicting results regarding treatment and overall prognosis.

The aim of this study was to evaluate whether radioactive iodine therapy after total thyroidectomy improves prognosis and survival in patients with HCC.

THE FULL ARTICLE TITLE
Wang X et al 2022 Radioactive iodine therapy does not improve cancer-specific survival in Hürthle cell carcinoma of the thyroid. J Clin Endocrinol Metab 107:3144–3151. PMID: 35908290.

SUMMARY OF THE STUDY
In this study, the authors used the U.S. Surveillance, Epidemiology, and End Results (SEER) database to identified patients diagnosed with HCC who underwent total thyroidectomy between 2000 and 2018. Among the 2279 patients included in the study, 1438 (63%) received radioactive iodine therapy treatment after their thyroid surgery.

The patients who received radioactive iodine therapy were younger (average age: 54 versus 56 years), had larger cancers (average cancer: 3.8 versus 3.5 cm), showed more frequent cancer extension outside the thyroid gland (17% versus 13%), and had more advanced disease including spread outside the neck (16% versus 12%) as compared to those who did not receive radioactive iodine therapy. To control for sex, age, race, year of diagnosis, cancer staging, spread outside the neck, and spread to the lymph nodes, a new patient sample was selected from the initial study group that included 733 patients.

The primary study outcome was cancer-specific survival (CSS), calculated as the time from the initial diagnosis to death from thyroid cancer, last follow-up or 12/31/2018, the first occurring event being chosen for each patient. In the entire group, disease-specific death occurred in 125 patients (5.5%) during an average follow-up time of 92 months. The CSS rates for the entire group were 97% at 5 years, 93% at 10 years, and 90% at 15 years. There was no difference in CSS rates between patients who received radioactive iodine therapy and those who did not when examining the entire group or the matched group. Increased age (55 years or older), larger cancer size (larger than 4 cm), and more advanced cancer were associated with a higher disease-specific mortality. Radioactive iodine therapy treatment also did not improve the CSS rates in patients with more aggressive cancer features.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
In this large SEER-based study, patients with HCC who underwent total thyroidectomy had overall an excellent cancer-specific survival. Older patients with larger cancers or more advanced cancer stage had increased disease-specific mortality. However, there was no difference in cancerspecific survival noted between patients who received and those who did not receive radioactive iodine therapy after total thyroidectomy.

— Alina Gavrila, MD, MMSC

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