CORONADO, CALIF. – The use of radioactive iodine in patients with papillary thyroid cancer showed a small but statistically significant survival benefit for all tumor size categories, a long-term analysis of national data suggested.
“The incidence of papillary thyroid carcinoma is rapidly rising, but the survival advantage of radioactive iodine ablation has not been confirmed,” Dr. Paritosh Suman said at the annual meeting of the American Thyroid Association.
To investigate the effect of radioactive iodine (RAI) on papillary thyroid cancer mortality, Dr. Suman and his associates identified 108,565 patients from the National Cancer Data Base who were diagnosed with papillary thyroid cancer and underwent total or near total thyroidectomy between 1998 and 2006.
The investigators classified tumors into one of four groups by diameter size: 10 mm or less, 11-20 mm, 21-40 mm, and greater than 40 mm. The study researchers used Cox regression analysis to quantify the effect of radioactive iodine, adjusting for clinicopathologic, demographic, and socioeconomic variables. A total of 52% of the patients were older than 45 years, 77% were female, and 54% received RAI.
Factors predicting the use of RAI were being male, having positive margins, having cervical lymph node involvement, and having a tumor size greater than 4 cm in diameter, said Dr. Suman, an endocrinology surgery fellow at North Shore University Health System in Evanston, Ill. The 10-year overall survival rate was 90% in those who received RAI, compared with 87.4% among those who did not, for a small but statistically significant survival advantage (P < .0001).
Among patients who received RAI, the 10-year survival advantage by diameter of tumor was 3.4% for those with tumors 10 mm or less; 2.8% with 11-20 mm; 3.3% with 21-40 mm, and 5.7% with greater than 40 mm.
Age also played a factor, with a 10-year survival advantage of 0.5% for those aged 18-35 years; 1.5% for those aged 36-45 years; 0.9% for those aged 46-55 years; 0.6% for those aged 56-65 years; and 2.1% for those older than 65 years. Both men and women who received RAI had a statistically significant survival advantage at 10 years (3.9% and 1.6%, respectively).
When the researchers assessed the 10-year survival advantage by lymph node category of patients who received RAI, the rates were 2.9% for N-0, 4.2% for N-1, 5.2% for N-1A, and 5.8% for N-1B. By margin status, the 10-year survival advantage was 3.1% for negative margins, 3.6% for positive margins, 3.5% for microscopic margins, and 8.8% for gross margins.
In an analysis of all patients with very low-risk, low-risk, and high-risk papillary thyroid carcinoma according to ATA guidelines for the use of RAI, the study authors found a 10-year survival advantage of RAI in each of the three categories.
Among patients with very low-risk papillary thyroid carcinoma, the rate of 10-year survival was 92.2% among those who received RAI, compared with 89% among those who did not (hazard ratio, 0.74). Similar associations were observed in those with low-risk carcinoma (91.8% vs. 89%; HR, 0.80) and in those with high-risk carcinoma (86.2% vs. 79.2%; HR, 0.71).
“RAI is associated with a statistically significant but small overall survival advantage for most patients,” Dr. Suman said. “High-risk patients, defined by large tumor size, lymph node involvement, and gross margins, achieve the greatest benefit with RAI ablation.”
Dr. Suman reported having no relevant financial disclosures.
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