MONTREAL — Pediatric patients with low-risk differentiated thyroid cancer (DTC) who are spared radioactive iodine (RAI) therapy show no increases in the risk of remission compared with those who do receive it, supporting guidelines that recommend against use of RAI in such patients.
“In 2015, when the American Thyroid Association [ATA] created their pediatric guidelines [on RAI therapy in DTC], they were taking a leap of faith that these [pediatric DTC] patients would be able to achieve remission without RAI,” said first author Mya Bojarsky, Children’s Hospital of Philadelphia (CHOP), when presenting the findings at the American Thyroid Association (ATA) 2022 Annual Meeting.
“This is the first study to validate those guidelines and support the sentiment that for ATA low-risk pediatric thyroid cancer patients, withholding RAI therapy is clinically beneficial as it reduces exposure to radiation while having no negative impact on remission,” she said.
Prior to 2015, thyroidectomy in combination with RAI was the standard treatment for DTC in pediatric patients. However, data showing that radiation exposure in children increases the risk of secondary hematologic malignancies by 51% and solid malignancies by 23% over a lifetime raised concerns and led to a push to change the treatment approach.
In response, the 2015 ATA pediatric guidelines recommended that patients not receive RAI for the treatment of DTC that was mostly confined to the thyroid (N0 or minimal N1a disease).
Senior author Andrew J. Bauer, MD, noted that, in addition to being the first study to confirm that withholding RAI in low-risk patients is associated with the same rate of achieving remission as patients treated with RAI, the study also endorses that assessments at 1 year can be reliable predictors of remission.
“For these patients, the 1-year mark post-initial treatment (thyroidectomy) is an early and accurate time point for initial assessment of remission, with increasing rates of remission with continued surveillance (at last clinical follow-up) of approximately 90% 2 years post initial treatment,” said Bauer, medical director, CHOP, and professor of pediatrics, Perelman School of Medicine, University of Pennsylvania, Philadelphia.
“This approach has recently been validated through a prospective study in adult patients,” he added. A large recent study of 730 patients published in the New England Journal of Medicine supported the omission of RAI in low-risk DTC in adults, showing that compared with those who received RAI, the no-RAI group was noninferior in the occurrence of functional, structural, and biologic events at 3 years.
Safe to Eliminate RAI Therapy in Low-Risk DTC in Children
With limited data on how or if the change in treatment had an impact on rates of remission in pediatric patients, Bojarsky and colleagues conducted a retrospective cohort study of patients under the age of 19 years with ATA low-risk DTC who had undergone a total thyroidectomy at CHOP between 2010 and 2020.
Overall, they identified 95 patients, including 50 who had been treated with RAI in addition to thyroidectomy and 45 who did not receive RAI. Among those who did receive RAI, 31 were treated prior to 2015, and 19 were treated after 2019.
For the study, remission was defined as having undetectable thyroglobulin levels as well as no evidence of disease by ultrasound, Bojarsky said.
“This is important to show because we want to ensure that as we are reducing our RAI use in the pediatric population, we were not negatively impacting their ability to achieve remission,” she explained.
The percentage of low-risk pediatric patients with DTC treated with RAI had already dropped from 100% in 2010 down to 38% by 2015 when the guidelines were issued, and after a slight rise to 50% by 2018, the practice plummeted to 0% by 2020, the study shows.
In terms of remission, at 1 year post-treatment, 80% of patients who received RAI were in remission, and the rate was even slightly higher, at 84%, among those who did not receive RAI, for a difference that was not significant.
Further looking at disease status as of the last clinical evaluation, 90% in the group treated with RAI had no evidence of disease at a median of 4.9 years of follow-up, and the rate was 87% in the group not receiving RAI, which had a median of 2.7 years of follow-up.
“In ATA low-risk patients, there is no detriment in achieving remission if RAI therapy is withheld,” say investigators.
The median tumor size in the RAI group was larger (19.5 mm vs 12.0 mm; P < .001), and the primary tumor was T1 in 44% of the RAI group but 82% in the no-RAI group (P < .001).
The lymph node status was N0 in 72% of those receiving RAI and 76% in the no RAI group, which was not significantly different.
The leading risk factors associated with treatment with RAI included larger primary tumor size (OR, 1.07; P = .003), lymph node metastasis (OR, 3.72; P = .036), and surgery pre-2015 (OR, 9.83; P < .001).
RAI administration, N1a disease, and surgery prior to 2015 were not independent risk factors for evidence of persistent disease or indeterminate status.
Bojarsky has reported no relevant financial relationships.
ATA Annual Meeting. Late-Breaking Abstract #47. Presented October 20, 2022.