Thyroid Research Thyroid Research Archive Thyroid Cancer

Some patients with thyroid carcinoma benefit from radioactive iodine and external radiation therapy

(November 2005)

The background of the study. Patients with papillary or follicular thyroid carcinoma are treated in varying ways, particularly with respect to the extent of surgery, radioactive iodine (I-131) therapy, and external-beam radiation therapy directed to the neck. This study was done to determine the effect of variations in treatment on outcome in patients with thyroid carcinoma seen at a single hospital over a period of 40 years.

How the study was done. From 1958 to 1998, 729 patients with papillary or follicular carcinoma of the thyroid were seen at the Princess Margaret Hospital in Toronto. The extent of surgery varied. Most patients were also treated with a relatively low dose of I-131, and those in whom surgery was considered incomplete were usually treated with higher doses of I-131 and also radiation.

The results of the study. There were 539 women (74 percent) and 190 men (26 percent); 76 percent had papillary carcinoma and 24 percent had follicular carcinoma. Tumor size varied from <1 cm to >4 cm. There was extrathyroidal extension of the tumor in 50 percent, neck metastases in 39 percent, and gross disease after surgery in 9 percent; 72 percent were treated with I-131 and 44 percent with radiation.

The median follow-up was 11 years. The overall 10-year survival rate was 87 percent, and the 10-year local-regional relapse-free rate was 85 percent. Age <45 years, female sex, small tumor size, absence of gross residual disease after surgery, and absence of tumor spread on the first scan after treatment with I-131 were associated with a higher survival rate and a lower local-regional relapse rate. Overall, more aggressive surgery or I-131 therapy was not associated a higher survival rate, but I-131 therapy was associated with a lower local-regional relapse rate. Radiation therapy was associated with higher survival rates and lower local-regional relapse rates in some patient groups.

The conclusions of the study. Factors associated with a good prognosis in patients with thyroid carcinoma are younger age, female sex, and limited extent of disease. I-131 therapy and radiation therapy have benefit in some patients.

The original article. Brierley J, Tsang R, Panzarella T, Bana N. Prognostic factors and the effect of treatment with radioactive iodine and external beam radiation on patients with differentiated thyroid cancer seen at a single institution over 40 years. Clin Endocrinol (Oxf) 2005;63:418-27.