Radioactive Iodine Ups Survival for Thyroid Microcarcinomas

Nancy A Melville

November 12, 2014

SAN DIEGO — Radioactive iodine (RAI) shows benefit in improving overall survival among papillary-thyroid carcinoma patients across all tumor size categories, including the very smallest, according to new research presented here at the 2014 Annual Meeting of the American Thyroid Association.

"Radioactive-iodine ablation in papillary-thyroid cancer is associated with a statistically significant but small overall survival advantage for most patients," Dr Paritosh Suman (North Shore University Health System, Evanston, Illinois) told the meeting.

While papillary-thyroid carcinoma in general is associated with an excellent prognosis, its incidence is on the rise, and there is some debate over appropriate treatment across the various tumor sizes.

In addition to the standard treatment of surgical resection, RAI is recommended when the tumor size represents a high risk; however, there has been debate over its efficacy on smaller tumors.

These new findings will likely add to the debate over treatment of the smallest thyroid cancers. But there are some important limitations in terms of the survival data specifics, commented Dr Megan Haymart (University of Michigan Health System, Ann Arbor).

"I think the authors performed an interesting study that both adds to our knowledge and opens the door for additional questions," she told Medscape Medical News.

"The study will add to the controversy surrounding when to use radioactive iodine for thyroid cancer, [but] a major limitation is the fact that the database captures only overall survival, not disease-specific survival," she said.

"Most patients with papillary-thyroid cancer have an excellent prognosis and a low disease-specific mortality rate. It isn't clear from these data if radioactive iodine prevents death from thyroid cancer or if its receipt correlates with factors associated with improved survival, such as higher socioeconomics, fewer comorbidities, etc."

Benefit of RAI for Microcarcinomas Under Debate

Previous research shows RAI to offer a survival advantage only to patients with larger primary tumors with distant spread, including a study of nearly 15,000 papillary-thyroid carcinoma patients (J Surg Oncol. 2007;96:3-7.)

Dr Suman's team examined the role of tumor size in papillary-thyroid carcinoma mortality when treatment involves RAI; they evaluated data on 284,635 patients identified with this malignancy in the National Cancer Database between 1998 and 2011.

Tumor margins were negative in 79% of patents and positive in 12%. The highest percentage of tumors (31%) were 10 mm or less in size (microcarcinomas); 29% were 11 to 20 mm; 24% were 21 to 40 mm; and 8% were larger than 40 mm.

RAI was utilized in the treatment of 47% of papillary-thyroid carcinoma cases overall, including for 58% of those in whom tumor size was above 40 mm, compared with 29% of patients whose tumors were 10 mm or less (P < .001).

The results showed RAI was associated with improved overall survival for all tumor size categories.

"The overall 10-year survival in patients receiving RAI was 90%, compared with 87.4% in those who didn't receive RAI [P < .0001]," Dr Suman said.

Survival Advantage Remained After Multivariate Adjustment

The association of improved survival with RAI treatment remained after adjustment for variables including age, gender, tumor grade, operation received, TNM stage, insurance status, hormone suppression, and presence of positive margins, positive lymph nodes, and distant metastases, Dr Suman said.

Survival Benefit of RAI Treatment According to Tumor Size (Mean Follow-Up 7 Years)

Tumor size, mm Hazard ratio P
< 10 0.73 < .001
11–20 0.82 .04
21–40 0.63 < .001
>40 0.62 .001

The use of RAI was associated with the strongest 10-year survival advantage in people over the age of 65 (2.1% higher than without RAI); in males (3.9% higher, compared with 1.6% greater in females), and among those with tumor margins defined as gross (8.8% advantage).

But Dr Haymart underscored the importance of controlling for certain socioeconomic variables and comorbidities in such research; otherwise, incorrect assumptions may be drawn.

"For example, sicker patients who are going to die of another etiology may be less likely to get radioactive iodine," she explained. "If we don't control for comorbidities, it may look like not using radioactive iodine is associated with death."

The authors have reported they have no relevant financial relationships. Dr Haymart disclosed that she is a recipient of an award from the National Institutes of Health (National Cancer Institute) that is looking at understanding the use of radioactive iodine.

2014 Annual Meeting of the American Thyroid Association; October 30, 2014; San Diego, CA. Abstract 15.

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