BACKGROUND
Papillary thyroid cancer is the most common type of thyroid cancer. Most papillary thyroid cancers are low-risk cancers, meaning low risk for either cancer recurrence or cancer death. Until recently most thyroid cancers were treated with surgery to remove the whole thyroid then sometimes followed with radioactive iodine therapy. However, in most cases, papillary thyroid cancer is not very dangerous and patients do very well even when only the side containing the cancer is removed (lobectomy). Leaving the opposite lobe intact results in fewer side effects of treatment. The concern with this approach is missing small cancer spots in the other half. So, it is important to study how often the cancer comes back after surgery.

This study was done to find out how often there might still be papillary thyroid cancer in the other side of the thyroid when only one lobe was removed. The researchers also wanted to find out which factors make the cancer come back. They were especially looking for the effects of having cancer on both sides of the thyroid (bilateral cancer) or having more than one area of cancer in the same thyroid lobe (multifocal cancer).

THE FULL ARTICLE TITLE
Rodriguez Schaap PM et al 2023 Bilaterality, not multifocality, is an independent risk factor for recurrence in low-risk papillary thyroid cancer. J Natl Cancer Inst. Epub 2023 Jun 2. PMID: 37267155.

SUMMARY OF THE STUDY
The study was done in the Netherlands. Researchers reviewed information about patients who had surgery for low-risk papillary thyroid cancer between 2005 and 2015. They used two large nationwide databases to gather information. They included patients with low-risk papillary thyroid cancer who had part of their thyroid removed and then, within one year, the other part taken out.

Based on the number and location of the lesions patients were divided into 4 groups. Group A had one cancer in the thyroid, Group B had one cancer in the initial lobe and found to have cancer in the opposite lobe after the second surgery, Group C had multiple cancers in the initial lobe and no cancer in the opposite lobe, and Group D had multiple cancer in the initial lobe and multiple cancer in the opposite lobe.

There were 791 patients. Most of them were women (83%) and around 46 years old. Out of these patients, 460 of them had just one cancer spot, 103 had multiple cancers in one lobe of their thyroid, and 228 had cancer on both sides. The likelihood of finding cancer on the opposite side was 24.6% for patients who had one cancer and 43% for patients with multiple cancers in the lobe that was first taken out. The risk of the cancer coming back was 1.5% (7/460) for group A, 7.3% (11/150) for group B, 1.9% (2/103) for group C and 2.6% (2/78) for group D. When they further analyzed these findings, they found that having cancer on both sides of the thyroid was the only factor that made it more likely for the cancer to come back. The risk was 3.6 times higher for these patients.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
The authors concluded that there is a good chance of finding some cancer on the other side of the thyroid especially if there are multiple cancer spots in one lobe. They also concluded that having cancer on both sides of the thyroid is a bigger risk for the cancer coming back than having one cancer spot on one side. Overall, the chances of the cancer coming back is generally low.

For this type of thyroid cancer, a smaller surgery that removes only one side of the thyroid may be as good as a more extensive surgery. Having a smaller surgery and closely watching the other side of the thyroid may be a better option for some patients. The findings of this study can help us choose which patients would benefit from this approach. We still need more studies to better understand thyroid cancer and make safer treatment decisions.

— Ebru Sulanc, MD

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