Patients with thyroid cancer whose disease is at low risk of returning can be treated safely with a smaller amount of radiation following surgery, according to results from the HiLo trial presented by Wadsley et al at the 2018 National Cancer Research Institute (NCRI) Cancer Conference (Abstract LBA 2148).
Jonathan Wadsley, MB, BChir, MA, MRCP, FRCR, a consultant clinical oncologist at the Weston Park Hospital, Sheffield, UK, and Chair of the National Cancer Research Institute (NCRI) Thyroid Cancer Subgroup, said that the latest results from the HiLo trial showed there was no significant difference in the recurrence rate between patients given a low radiation dose compared to the standard, higher dose. He said this meant that international guidelines could be updated to recommend the lower dose in low-risk patients, and that these patients would benefit from fewer side effects, fewer long-term complications, and a more convenient treatment.
Results were from 434 patients with low-risk thyroid cancer in the HiLo trial with a median follow-up time of 6.5 years. Patients were randomly assigned to receive low administered radioactive iodine activity (RAI) of 1.1 GBq, or the standard high RAI of 3.7 GBq. They also received either thyrotropin alfa (Thyrogen, a genetically engineered thyroid-stimulating hormone, or TSH), which stimulates thyroid cancer cells to absorb as much radioactive iodine as possible, making it more effective, or they were asked to stop taking their thyroid hormone tablets, which achieves the same effect by allowing levels of their natural TSH to rise.
Dr. Wadsley explained. “Activity is a measure of the amount of radiation that is administered to the patient in the form of a radioactive isotope of iodine. The aim of the treatment is to destroy any residual normal thyroid tissue and thyroid cancer cells following surgery to remove the thyroid gland. The treatment is most commonly given as a capsule to swallow… In our study the low-activity 1.1-GBq dose was less than one-third of the higher-activity 3.7-GBq dose but has been proven to be as effective.”
During the nearly 7 years of follow-up, there were 21 recurrences of cancer (11 and 10 with 1.1 GBq and 3.7 GBq, respectively). The recurrence rates were similar between the two doses, as well as between patients using thyrotropin alfa and those experiencing thyroid hormone withdrawal.
“The study showed that patients receiving a lower activity experienced fewer side effects—in particular, less risk of feeling sick or suffering damage to the salivary glands, which can potentially lead to a permanently dry mouth. The use of a lower activity also raises the possibility of giving the treatment in 1 day rather than having to admit patients to be nursed in isolation for 2 to 3 nights. This is required for the higher activity due to radiation protection regulations to avoid exposing the general public to unnecessary radiation, but can be particularly distressing for patients as they can only have very limited contact with other people during this time, which is particularly hard for someone with a recent cancer diagnosis. Therefore, not only is lower activity preferable for patients, it can also result in cost savings to the health service,” said Dr. Wadsley.
He added, “The study also showed that quality of life and ability to continue normal activities was much better for patients receiving [thyrotropin alfa] than those using thyroid hormone withdrawal. If thyroid hormone withdrawal is used, patients have to come off their regular medication for at least 2 weeks. This leaves them feeling extremely tired and in some cases quite depressed.”
He said that the HiLo trial had the longest follow-up time of any other randomized study worldwide. Until now, there had not been enough evidence for international guidelines to do more than make weak recommendations about using 1.1 GBq in low-risk patients, due to the limited data and only short-term follow-up. “Now that we have confirmation that there is no difference in recurrence rates over a longer follow-up period, these recommendations can be strengthened, and clinicians and patients can be confident that use of the lower activity is acceptable and in fact preferable,” he concluded.
The HiLo trial has been completed, and now the researchers are investigating whether a group of patients can be identified that have such a low risk of recurrence of their thyroid cancer that they do not require radioiodine therapy at all. The IoN trial (Iodine or Not) is allocating patients with very low-risk thyroid cancer to have radioiodine therapy or careful observation alone to determine whether there is any difference in recurrence rates and whether these patients could avoid iodine treatment altogether.
Disclosure: See study authors’ full disclosures at conference.ncri.org.uk.
The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.