Radioiodine therapy of fine miliary lung metastases from differentiated follicular thyroid carcinoma

Abstract

Introduction

Differentiated follicular thyroid carcinomas (DTCs) have an indolent progression with an excellent overall prognosis. Nevertheless, 10–15% of patients develop lung metastases. Radioiodine therapy plays an important role in the diagnosis and treatment of these metastases.

Materials and methods

We reviewed retrospectively the records of patients who had synchronous fine miliary lung metastases at diagnosis of DTCs, between 1996 and 2016. All these patients underwent total thyroidectomy with or without lymph node dissection. They received ¹³¹I therapy courses, every 6–12 months if the disease showed ¹³¹I uptake and remained clinically responsive. Evaluation of treatment efficacy was based on clinical, biological, and post-treatment data.

Results

Fourteen patients were included. They were 3 men and 11 women. Age ranged from 5 to 65 years old (average age was 27.6 years old). Half of them were children. Lung metastasis revealed the diagnosis in one case. Papillary carcinoma was the most frequent histological type, seen in eleven patients. Lymph node involvement was found in eleven patients. Anatomopathological study showed vascular emboli in nine patients, capsular invasion in ten cases and extrathyroidal microscopic extension in eight cases. The tumour was bilateral in six cases and multifocal in ten cases. The average tumour's size was 37.4 ± 24.7 mm, with extremes ranging from 5 to 80 mm. Chest radiographs, performed in seven patients, were normal in five cases. Diffuse miliary was found in one case. ¹³¹I — whole body scan (WBS) detected the fine miliary metastases in all cases. The initial thyroglobulin level ranged from 24 to 7000 ng/ml and it was above 100 ng/mL in 10 cases. The number of courses varied from 3 to 12 times with a mean of 6. The cumulative activity was 24.6 ± 9.4 GBq, with extremes ranging from 11.1 to 42.7 GBq. The response to radioiodine therapy was complete in 8 patients, partial in 4 others and absent (tumour progression) in the last two patients. Pulmonary fibrosis was observed in four patients.

Conclusion

Fine miliary lung metastases from DTCs are rarely revealed on chest radiographs and they are mainly seen on post-therapeutic WBS. They are more common in children and young adults with good sensitivity to radioiodine and a good long-term prognosis. Achieving complete treatment in lung metastases is not easy. However, pulmonary fibrosis with impaired pulmonary function after radioiodine therapy remains fearsome.