TORONTO—Radioactive iodine has been used traditionally as an adjuvant treatment for high-risk differentiated thyroid cancers. But the treatment is best reserved for metastatic disease because it does not bolster survival rates in patients with locally advanced disease or when resection is incomplete, according to a study from the University of Manitoba.
“Radioactive iodine [RAI] certainly has a role in metastatic disease, but it's not a substitute for inadequate surgery; you can’t leave the disease behind and hope that radioactive iodine will take care of that,” said study author K. Alok Pathak, MD, an associate professor of surgery.
Dr. Pathak and colleagues assessed whether RAI treatment actually improved disease-specific survival (DSS). Their study included 277 patients (mean age, 56) with high-risk differentiated thyroid cancer who were treated between 1970 and 2005. The patients were considered to be at high risk on the basis of AMES (age, metastases, extent, and size) criteria. The majority (60%) had total thyroidectomy, while 40% were managed by thyroid-stimulating hormone (TSH) suppression only. Fifty-seven percent of the patients underwent therapeutic, high-dose RAI treatment (2009 World Congress on Thyroid Cancer session 6).
Of the patients who had RAI treatment, 34.4% had disease that failed to respond and 9.8% died of their disease. In comparison, among patients who did not have RAI treatment, 17.6% failed to respond to their treatment and 7.8% died of their disease. On multivariate analysis, DSS was independently influenced by tumor grade (hazard ratio [HR], 463.9; P = .014), completeness of resection (HR, 108.4; P = .014), distant metastases (HR, 345.8; P = .016), and age at diagnosis (HR, 1.1; P = .08). The use of adjuvant RAI treatment did not have a significant impact on DSS.
Dr. Pathak and colleagues concluded that RAI therapy does not appear to offer any survival advantage over TSH suppression in high-risk differentiated thyroid cancer.
“Thyroid cancer is a cancer which is an entirely different spectrum of disease. We cannot compare it to squamous cell cancer in the head and neck because the outcome is very different,” Dr. Pathak told Oncology News International. “Thyroid cancer patients, even with persistent disease, can keep on surviving for years. We don’t know whether microscopic residual disease, which we are aiming to treat with radioactive iodine, has a long-term impact on survival. Evidence is starting to show that it does not. The issue needs to be looked at critically, because so many patients are affected.”
RAI may benefit a select group of patients
The role of RAI treatment in thyroid cancer has been a source of controversy for some time, said Dr. Shah, professor of surgery at Memorial Sloan-Kettering Cancer Center in New York.
“It certainly offers no benefit to ‘high-risk’ patients with poorly differentiated carcinoma,” he said. “It also has a very questionable role, since these cancers are not iodine-avid. Besides, it is a treatment that leaves a significant number of patients with xerostomia and episodes of recurrent sialadenitis as well as an increasing risk of a second primary cancer with increasing doses of radioiodine.”
However, Dr. Shah pointed out, RAI has shown benefit in pediatric papillary carcinomas and adults with iodine-avid, bulky nodal metastases or distant metastases. “In the high-risk group, it may benefit only a select group of patients with advanced, iodine-avid cancer as an adjuvant treatment after complete removal of all gross disease,” he said.