BACKGROUND
Thyroid cancer is the fastest rising cancer. Papillary thyroid carcinoma is the most common type of thyroid cancer and follicular thyroid carcinoma is the second most common. Together they make up 90+% of all thyroid cancer. Risks for recurrence (when the cancer comes back after treatment that was successful in destroying the cancer) of papillary thyroid carcinoma are well known. In contrast, follicular thyroid carcinoma is a lot less common than papillary thyroid carcinoma, and risk factors for recurrence of follicular thyroid carcinoma are not well defined. Papillary thyroid carcinoma and follicular thyroid carcinoma are often grouped together even though they differ in presentation and clinical behavior. In contrast to papillary thyroid carcinoma, follicular thyroid carcinoma recurs more frequently with distant metastases (where the cancer spreads to other organs far away from the thyroid) than involvement of neck lymph nodes (small organs found in the neck and also in other locations). The purpose of this study is to systematically review the risk factors for follicular thyroid carcinoma recurrence.

THE FULL ARTICLE TITLE
Grønlund MP et al Risk factors for recurrence of follicular thyroid cancer: A systematic review. Thyroid. Epub 2021 Jul 5. PMID: 34102860.

SUMMARY OF THE STUDY
A systematic literature search was performed in September 2020 of studies evaluating risk factors for follicular thyroid carcinoma recurrence. A total of 9 studies with a total of 1,544 patients from eight countries were included in this review. Risk factors examined in the studies included sex, age at diagnosis, primary cancer size, invasiveness (spread into the thyroid capsule and into blood vessels), positive resection margin (presence of leftover tumor after surgery), spread to the lymph nodes and spread outside the neck at diagnosis. The average follow-up time ranged from 5 to 23.7 years. The average rate of recurrence was 13.6% ranging from 2 to 29%. In 64.8% of recurrent cases, spread outside the neck was noted. Age greater than 45 years, primary cancer size greater than 4 cm, increased invasiveness, multiple nodules in the thyroid with the cancer, positive resection margin, spread to the lymph nodes in the neck and spread outside the neck were all identified as risk factors associated with follicular thyroid carcinoma recurrence.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
Risk factors for recurrence of follicular thyroid carcinoma were identified. Age and multifocal disease had more of an impact on the risk of recurrence of follicular thyroid carcinoma than in papillary thyroid carcinoma. Future studies on follicular thyroid carcinoma are needed to better understand risk for cancer recurrence.

— Priya Mahajan, MD

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