BACKGROUND
Thyroid cancer is the most common endocrine cancer. When thyroid cancer spreads outside of the thyroid, it most often ends up in the lymph nodes in the neck. However, thyroid cancer can spread through the body by invading blood vessels, which is called vascular invasion. Follicular thyroid carcinoma and Hürthle-cell carcinoma are closely related thyroid cancer subtypes that are known to spread by vascular invasion. While only 10% of all thyroid cancer cases are follicular cancers and 5% from Hürthle-cell cancers, they are both felt to be more severe than other cancer subtypes such as papillary thyroid cancer, the most common type of thyroid cancer. However, there is very little data comparing outcomes such as overall survival, cancer recurrence and distant cancer spread between these two cancer subtypes. In particular, scientists still are not sure how the extent of vascular invasion affects one’s prognosis.

This study examined how the degree of vascular invasion affects the clinical outcomes of patients with follicular cancer compared to Hürthle-cell thyroid cancer.

THE FULL ARTICLE TITLE
Matsuura D et al 2022 Follicular and Hürthle cell carcinoma: Comparison of clinicopathological features and clinical outcomes. Thyroid 32:245–254.

SUMMARY OF THE STUDY
The authors studied 190 patients with follicular thyroid carcinoma and Hürthle-cell carcinoma treated at Memorial Sloan Kettering Cancer Center in New York City between 1986 and 2015. First, the pathology slides were reviewed by specialists who did not know each patient’s clinical outcome.

Next, each case was classified into four groups depending on the degree of vascular invasion: minimally invasive; focal vascular invasion, extensive vascular invasion and widely invasive. Then they compared important clinical outcomes such as overall survival, disease-specific survival, and recurrence-free survival between the various groups.

There were 111 patients with Hürthle-cell cancer and 79 with follicular thyroid cancer. Patients with Hürthle-cell cancer were more likely to be older than 55 and tended to present with more extensive vascular invasion than with follicular cancer (33% vs. 19%). Regardless of the type of thyroid cancer, patients with extensive vascular invasion had worse recurrence rates compared with focal or no vascular invasion (10-year recurrence-free survival 77% if extensive vascular invasion, 95% if focal vascular invasion and 100% if no vascular invasion). In addition, patients with Hürthle-cell cancers with extensive/ wide vascular invasion were more likely to experience a recurrence of their cancer than follicular thyroid cancer with extensive/wide vascular invasion (10-year recurrence- free survival 98%, vs 78%).

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
Hurthle-cell carcinoma appears to be a more severe cancer subtype than follicular thyroid cancer. The degree of vascular invasion is a particularly important factor that affects the behaviour of Hürthle-cell cancer, as Hürthlecell cancers with significant vascular invasion have high recurrence rates and more frequent spread outside of the neck. Therefore, Hürthle-cell carcinoma may require more aggressive treatment strategies such as total thyroidectomy and radioactive iodine therapy.

— Phillip Segal, MD

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