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 (131)I ablation for lung invasion and (2) the survival of patients receiving periodic (131)I 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 (131)I ablation. Functioning pulmonary metastases occurred in 20 patients. All these patients received periodic (131)I therapy for as long as (131)I 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 (131)I 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 (131)I uptake, and the other eight are in apparent remission after receiving an average cumulative (131)I 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 (131)I therapy. Early diagnosis, during post-surgery (131)I scanning, of radiologically inapparent metastases is associated with a better prognosis.