Pediatric patients with thyroid cancer are at increased risk for a second cancer if they receive radioactive iodine therapy. A publication in Thyroid (the leading peer-reviewed journal) from June of 2015 involved 3,850 patients who underwent surgery and either did or did not receive radioactive iodine after surgical treatment. The research found a 42% increased risk for a second primary cancer amongst all the patients who were treated with radioactive iodine. No equivalent excess risk was noted in the patients who did not receive radioactive iodine.
Salivary Glands Are at Highest Risk
Salivary cancers had the largest increase in risk from the radioactive iodine. The reason for this is that the radioactive iodine molecules will kill any cell that takes up that molecule. If there is not enough thyroid tissue to uptake all of that radioactive iodine, then the iodine will go somewhere. The most avid tissue after thyroid to take up iodine molecules are the salivary glands. So, what you see with the administration of radioactive iodine is that the salivary glands take up the excess radioactive iodine and therefore are permanently damaged. This not only leads to dry mouth which can be permanent and very bothersome, but it also leads to an increase of salivary gland cancer.
In Kids, There Is A Risk of Second Cancers
The younger the patient, the more risk there is that they can subsequently develop cancer in these areas. A study in Thyroid journal in May of 2009 also showed a risk of a second primary cancer after RAI treatment in patients who had thyroid cancer. The authors showed that the relative rate for a second thyroid cancer was significantly increased. There was also a relative risk of leukemia that was increased in thyroid cancers treated with RAI with a relative risk factor of 2.5. Both are serious potential complications from radioactive iodine therapy. So, does that mean we should never use RAI? This is clearly an individual decision that must be weighed between the thyroid surgeon and the patient. There are certainly reasons to use radioactive iodine in high risk or moderate risk patients. These are patients who may have residual disease or a particularly aggressive form of thyroid cancer and the risk involved with radioactive iodine may be worthwhile to achieve a cure of the thyroid cancer. However, in relatively low risk situations, radioactive iodine should be avoided. While in days past, radioactive iodine was given to nearly everyone who had thyroid cancer, this should not be the case today. The increased risk of cancer certainly gives us pause and the decision for radioactive iodine should be carefully weighed.