CORONADO, CALIF. – In a large cohort of patients with differentiated thyroid cancer, the use of radioactive iodine was associated with improved disease-specific survival in those with advanced disease but not in those with papillary thyroid microcarcinoma.
“Everything in medicine is a risk-benefit balance,” lead author Dr. Ryan K. Orosco said in an interview in advance of the annual meeting of the American Thyroid Association, where the work was presented. “Any two patients that receive radioactive iodine (RAI) for differentiated thyroid cancer are likely to have different survival benefit from that therapy. This study provides a quantitative comparison of the impact of RAI in various patient subgroups.”
In one of the largest studies of its kind, Dr. Orosco of the division of head and neck surgery at the University of California, San Diego, and his associates identified 85,740 patients with differentiated thyroid carcinoma from the Surveillance, Epidemiology, and End Results database from 1973 through 2009. They used multivariate analyses to explore the association between RAI and cancer-specific survival in 149 population subgroups, controlling for age, decade of diagnosis, race, gender, tumor type, nodal involvement, metastasis stage, and RAI therapy.
More than three-quarters of the patients (78%) were female, 68% were white, their mean age at diagnosis was 46 years, and the median follow-up time was 85 months. The researchers found that nearly half of patients (43%) received RAI. By American Joint Committee on Cancer stage, RAI was used in 55% of stage I patients, 41% of stage II patients, 94% of stage III patients, and 85% of stage IV patients. In addition, 42% of patients with T1a disease and 88% of those with T4 disease received RAI.
Use of RAI was positively associated with survival in the overall cohort (hazard ratio 1.3; P = .002), while statistically significant HRs for RAI were observed in 49 population subgroups. In patients with metastatic disease, use of RAI was associated with a decreased risk for disease-specific mortality (HR range of 2.28-3.82). Protective effects of RAI were also observed in patients with regional metastases (HR 1.4-1.9), those with T3-positive tumors (HR 1.36-1.39), those with T4 tumors (HR 1.85), and in those with stage IV disease (HR 1.47-1.73).
Dr. Orosco and his associates observed a negative effect of RAI in patients with macropapillary carcinoma. Specifically, those with T1a disease had an increased likelihood of thyroid cancer–specific mortality (HR .13; P less than .001), while similar associations were seen in multiple subgroups of patients with T1a disease (HR 0.04-0.25). No statistically significant effects of RAI were observed in patients with T1b or T2 tumors.
“RAI appears to offer the best survival impact in patients with advanced differentiated thyroid carcinoma,” Dr. Orosco said. “Its use in early-stage patients should be carefully considered.”
In their abstract, the researchers noted that the findings “might help clinicians personalize RAI therapy to specific differentiated thyroid cancer populations – offering treatment in patients most likely to benefit, and sparing others unnecessary costs and potential side effects.”
Dr. Orosco acknowledged certain limitations of the study, including the fact that the SEER database does not contain details about each patient’s surgery, the dose of RAI used, other comorbidities, or data on cancer recurrence. “This study does not attempt to explore the reasons behind the apparent survival disadvantage seen in patients with T1a disease,” he said. “We don’t know exactly why early-stage patients have an increased risk of disease-specific mortality when RAI is used. Additional work is needed to explore this further.”
Dr. Orosco reported having no financial disclosures.
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