BACKGROUND
Thyroid cancer in children is different than in grown-ups. When children have thyroid cancer, the cancer is often at an advanced stage and has spread more throughout the body compared to adults. In adults, advanced stage thyroid cancer means there is an increased risk of the cancer coming back after treatment. The good news is that children with thyroid cancer usually get better regardless of the stage at presentation and have a very low chance of dying from it. Overall, the prognosis for patients with thyroid cancer is excellent in all patients but is better in children than in adults.

Because of these differences, it is important to study thyroid cancer in children separately from adults. The information we learn about thyroid cancer in adults may not be true for children and may result in giving too much treatment. For example, radioactive iodine therapy used as a treatment for thyroid cancer may have a higher risk at causing future health problems in children than in adults, like getting another type of cancer much later.

This study was done to better understand how thyroid cancer behaves in children and to figure out which factors could cause bad outcomes.

THE FULL ARTICLE TITLE
Review of: Saliba M et al 2022 Clinicopathologic and prognostic features of pediatric follicular cell-derived thyroid carcinomas: A retrospective study of 222 patients. Am J Surg Pathol 46:1659–1669. PMID: 36040037.

SUMMARY OF THE STUDY
The researchers looked at information from a group of 222 patients who were diagnosed with thyroid cancer before the age of 21 and treated at Memorial Sloan Kettering Cancer Center from 1994 to 2018. They collected data about their surgeries, like how much of the thyroid gland was removed and if lymph nodes were checked. They also studied specific things about the cancers, like their size, where they were located, how they looked under the microscope, if they had spread to lymph nodes or other parts of the body. They classified the cancers using the World Health Organization guidelines but there were also a few types described in a newer system. They wanted to understand which factors were related to a higher risk of the cancer coming back or spreading.

They also looked at factors like the patients’ age, gender, stage of the cancer, and outcome of the treatment. The main thing they wanted to know was how long the patients remained cancer-free after having their thyroid removed. The researchers also wanted to learn if the cancer came back in the same area, or if it spread to other parts of the body.

Thyroid cancer was more common in girls (78%). Age did not affect how serious the cancer was. Most of the group (79%) had papillary thyroid carcinoma (PTC). In almost two thirds of the patients, the cancer had spread to nearby lymph nodes. This was more common in boys and in cancer larger than 4 cm. Cancer that was surrounded by a protective layer was less likely to invade lymph nodes. A total of 14 patients (6%) had cancer that had spread to other parts of the body at the time of diagnosis. They found that a type of papillary thyroid cancer called tall cell variant behaves much less aggressively in children compared to adults. While this is an aggressive type in adults, in children it behaved similar to low-risk papillary thyroid cancer. They found that two subtypes of thyroid cancer had worse outcomes. The diffuse sclerosing variant of papillary thyroid cancer and high-grade follicular cell thyroid carcinoma with necrosis (cell death) were more serious and had a very high chance of spreading to lymph nodes.

Overall, being a boy, having a high-risk type of cancer, having a cancer larger than 4 cm, having cancer outside of the thyroid, having cancer cells at the edges of the removed tissue, and having necrosis in the cancer were associated with worse outcomes.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
Based on the findings, the researchers suggested that the classification of high-risk thyroid cancers in children should be based on specific criteria, mainly cancer necrosis (dead tissue) and certain subtypes of the cancer. They also point out that more research on the genes and characteristics of the cancer could help us better understand the disease. In conclusion, this study gives us valuable information about how thyroid cancer behaves in children and how it differs from the thyroid cancer in adults. It shows that we should think about thyroid cancer in children differently and not use information from studies of adults with thyroid cancer. It also reminds how important it is to have accurate ways of classifying the type of cancer a child has in order to plan the best treatment for them.

— Ebru Sulanc, MD

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