Functioning pulmonary metastases of thyroid cancer:: does radioiodine influence the prognosis?

Functioning pulmonary metastases are the most common distant lesions of differentiated thyroid cancer. About 50% of patients with such metastases die within 10 years. The impact of iodine-131 therapy is controversial. In this study we examined: (1) the early diagnostic value of post-surgery I-131 ablation for lung invasion and (2) the survival of patients receiving periodic I-131 therapy. Between January 1970 and December 1995 we provided initial treatment for 509 patients with thyroid cancer. Most of them (74%) underwent total thyroidectomy and I-131 ablation. Functioning pulmonary metastases occurred in 20 patients. All these patients received periodic I-131 therapy for as long as I-131 uptake persisted. Additional therapy consisted of lung surgery in three patients and local treatment of bone lesions in four patients. Follow-up data were recorded up to December 2001. Functioning pulmonary metastases occurred late in one patient, and were visible on the post-surgery I-131 therapy scan in the other 19 patients. At diagnosis of lung invasion, 11 patients had negative chest X-ray findings, and serum thyroglobulin levels were not suggestive of metastatic disease in 56% of these cases. One of the 11 patients with negative chest X-ray findings died with a neck recurrence, two have persistent pulmonary I-131 uptake, and the other eight are in apparent remission after receiving an average cumulative I-131 activity of 338 mCi (12.51 GBq). The nine patients with positive chest X-ray findings received an average of 939 mCi (34.74 GBq); two of them died, five are continuing to receive therapy and two are in apparent remission. Overall survival at 10 years is 84%. The average follow-up of the 17 survivors is 12.7 years. These results suggest that patients with functioning pulmonary metastases, even in advanced stages, may survive for many years on I-131 therapy. Early diagnosis, during post-surgery I-131 scanning, of radiologically inapparent metastases is associated with a better prognosis.