FFor decades, radiation therapy has been the cornerstone of thyroid cancer care. But it may soon be phased out entirely for many thyroid tumors as emerging research casts doubt on its benefit for patients.
A study published Wednesday in the New England Journal of Medicine suggests that surgery alone may be enough to cure the lowest-risk thyroid cancers, and that follow-up treatment with radioactive iodine offers no additional benefit for these patients.
“It’s almost a given that once patients have their thyroid removed, they get radioactive iodine,” said David Cooper, an endocrinologist at Johns Hopkins University School of Medicine. “Recently, people are wondering if it really does what it’s supposed to do, if its potential damage is worth the potential benefit.”
Part of the problem with answering this question is that low doses of radioactive iodine, which are typically given for low-risk thyroid cancer, aren’t that bad. Classically, radioactive iodine can cause nausea, malaise, or in some cases damage to the salivary glands, but many patients won’t even feel that, Cooper said.
The main burden is that the procedure costs time and money, and carries the small risk that the radiation itself could cause another cancer.
“Some patients may have a significant portion of the co-pay. It is very time consuming, which can affect the patient’s income. But the [medical] the risks are pretty low,” Cooper said. “That’s why it kind of drifted off without anyone analyzing it carefully.”
Radioactive iodine works like a Trojan horse against cancer. The thyroid needs iodine to produce its specific set of hormones, so thyroid cells and thyroid cancer cells pump out radioactive iodine-131 as readily as any other isotope of the element. Once inside, the radioactivity kills the cell. The idea is to clean out any thyroid cancer cells that may have been left behind after surgery, especially for cancers known as differentiated thyroid cancers, which include follicular and papillary thyroid cancer. Radioactive iodine is not used for other forms, such as medullary or anaplastic thyroid cancer.
“In the 1990s, there was a prospective study showing that radioactive iodine could reduce mortality and relapses in patients with thyroid cancer,” said Sophie Leboulleux, an oncologist who has worked on the studied as a scientist at the Gustave-Roussy cancer campus in France and is now at the University Hospitals of Geneva. “But times have changed. Thyroid cancers are not discovered at the same stages as 25 years ago.
Thyroid cancer is found more frequently now because CT scans and ultrasounds done on the head and neck for other reasons can also catch thyroid cancer. Often these are small, low-risk tumors, Leboulleux said. In these cases, clinicians began to wonder if surgery alone would be enough, saving patients the added cost of radiation therapy. In 2012, Leboulleux worked on another study that found roughly 30 millicuries of radiation was just as good as a much larger dose usually given for low-risk thyroid tumors.
“For people at low risk [thyroid cancer] we felt there might not be a need,” she said. “So we decided to do another study to see if radioactive iodine therapy was even helpful.”
So Leboulleux and his colleagues recruited 730 patients with low-risk differentiated thyroid cancer with tumors 2 centimeters or less in width. Half of them were randomly sorted to not receive radioactive iodine after thyroid surgery, and the other half received about 30 millicuries of radiation. After three years, there was no difference between the two groups with regard to new treatments, relapses or abnormal biological markers. The team will continue to follow study participants for several more years, but Leboulleux expects no change.
The study is the first hard evidence that postoperative radioactive iodine is most likely unnecessary for these low-risk thyroid cancers, said Johns Hopkins’ Cooper, who also wrote a editorial on the study. “The current recommendation is not to give radioactive iodine to low-risk patients like these, but it’s based on weak evidence and expert opinion,” Cooper said.
“This article will not change the recommendation, but doctors and scientists accept randomized trials. So I think it’s going to change hearts and minds on this subject,” he said. This should help doctors and patients feel more comfortable forgoing radiation therapy after thyroid surgery, Leboulleux said. Ultimately, she thinks it will be good for patients.
“Radiotherapy is just one more worry for a patient. Once you know you don’t need it, I don’t think you should receive it,” Leboulleux said.
Radioactive iodine always helps with high-risk thyroid cancer, where the malignancy has already spread throughout the body. Whether follow-up radiation therapy is beneficial for more intermediate-risk thyroid cancers remains an open question, Leboulleux added. This is something she hopes to study next.