Clinical outcomes and risk stratification for papillary thyroid carcinoma presenting with distant metastasis before the era of tyrosine kinase inhibitors.

Radioactive iodine (RAI) therapy has been the mainstay of treatment for papillary thyroid carcinoma (PTC) patients with distant metastasis (DM). Although tyrosine kinase inhibitors (TKIs) were introduced for the treatment of RAI refractory metastatic thyroid carcinoma several years ago, clinical outcomes for PTC patients with DM treated using RAI therapy remain unclear. We retrospectively examined 64 PTC patients (9 men, 55 women) with DM at diagnosis treated using RAI therapy without administration of any kind of chemotherapy or TKIs. Median age of patients was 58 years. Site of DM was the lungs (n = 59), bone (n = 3), and pleural dissemination (n = 2). No patients showed multiple-organ metastases at diagnosis. By the end of the study period, 21 patients had died of PTC. Cause-specific survival rates at 10, 15, and 20 years after initial surgery were 68.2%, 63.6% and 61.1%, respectively. Uni- and multivariate analyses identified age ≥55 years (HR 3.1, p = 0.023), site of DM other than the lungs (HR 13.4, p < 0.0001), and DM with no RAI avidity (HR 5.1, p = 0.0098) as factors independently associated with disease-related death. When analyses were restricted to patients with lung metastasis (n = 59), surgical non-curability was another independent risk factor (HR 5.2, p = 0.0047) in addition to age and RAI avidity. According to risk stratification analysis based on these risk factors, patients with site of DM other than the lungs or with lung metastasis showing ≥2 risk factors among age ≥55 years, DM with no RAI avidity, and surgical non-curability are expected to show higher mortality rates.