BACKGROUND
Cancer can sometimes develop in the thyroid gland, a butterfly- shaped organ located in the front of the neck that produces thyroid hormone. The most common kind of thyroid cancer is called papillary cancer and, if this cancer is not identified and surgically removed, it can spread out of the thyroid, usually to lymph nodes that sit next to the thyroid gland in the neck. Surgery to remove the thyroid gland, and the surrounding lymph nodes, is then needed to treat this problem. People for whom this surgery is performed are then monitored over time because thyroid cancer can sometimes come back, usually in one or more new lymph nodes in the neck. This is called recurrent thyroid cancer and it happens in 20-30% of people who are initially treated with surgery for thyroid cancer. When this happens, the new cancerous neck lymph node(s) are usually removed with more surgery. Additional surgery like this, however, has a relatively high risk of complications, because the area of the neck involved is usually scarred and distorted as a result of healing from the first surgery. This means that the chances of damaging normal neck structures (nerves, blood vessels, parathyroid glands, the windpipe, etc.) while removing these new cancerous lymph node(s) is higher than during the first surgery. In addition, some people who develop recurrent thyroid cancer may have other significant health problems (such as severe heart or lung disease) that make more surgery dangerous. For these reasons, new ways of treating recurrent thyroid cancer that do not involve surgery are currently being tested.

One way of treating recurrent thyroid cancer without surgery is to use heat to try and destroy the involved lymph node(s) (thermal ablation). This is done by inserting a fine needle through the skin into cancerous lymph node(s). The tip of this needle then delivers heat to the lymph node, burning the lymph node from the inside out and, as a result, hopefully destroying the cancer cells inside the node. There are three different ways that heat is delivered by the inserted needle: radiowave-based heat (radiofrequency ablation, RFA), microwave-based heat and laser-based heat. The authors of the research described here sought to study the effectiveness and safety of thermal ablation for treatment of recurrent thyroid cancer.

THE FULL ARTICLE TITLE
Zhang X et al 2022 Ultrasonography-guided thermal ablation for cervical lymph node metastasis of recurrent papillary thyroid carcinoma: Is it superior to surgical resection? Front Endocrinol (Lausanne) 13:907195. PMID: 35832431.

SUMMARY OF THE STUDY
The authors of this work searched current medical databases for previously published studies that examined thermal ablation for treatment of recurrent thyroid cancer in people older than 18 years. They were able to identify 18 different studies that evaluated this treatment method, 10 using radiofrequency ablation, 4 using microwave ablation and 4 using laser ablation. For the combined studies, the authors used statistical testing to look at the effectiveness and safety of thermal ablation, as measured by how much smaller treated lymph nodes became after thermal ablation (volume reduction rate), the extent to which blood markers for thyroid cancer (thyroglobulin) decreased after thermal ablation and complications that happened because of thermal ablation.

In terms of volume reduction, they found that treated lymph nodes become significantly smaller, with an average volume reduction rate of 88.4%. For thyroglobulin levels, the authors identified a significant decrease in these levels after thermal ablation of cancerous lymph nodes. Finally, 5% of people included in this study experienced a complication related to thermal ablation treatment. Voice changes related to nerve injury were the most common complications identified, occurring in 6.23% of people undergoing thermal ablation, and were particularly associated with thermal ablation done for lymph nodes in the center area of the neck (where the nerves that control the vocal cords are located).

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
The authors found that thermal ablation, by either RFA, microwave or laser, appears to be an effective alternative to surgical removal for treatment of recurrent thyroid cancer, at least in the short term, among people who choose not to undergo, or are not able to safely undergo, surgery. The study investigators did identify a risk of complications that can happen during thermal ablation, with the most common of these being temporary or even permanent voice changes resulting from injury to the nerves that control the vocal cords. Overall, these risks were found to be relatively low, suggesting that thermal ablation a reasonable option when surgery is not feasible for the treatment of recurrent thyroid cancer.

— Jason D. Prescott, MD PhD

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