Papillary thyroid carcinoma: prognostic factors and the role of radioiodine and external radiotherapy

PURPOSE: To evaluate the role of radioiodine and external radiotherapy treatment in papillary thyroid carcinoma (PTC). METHODS AND MATERIALS: This is a retrospective study of 842 patients with the diagnosis of PTC registered from 1960 to 1997 at the Department of Clinical Oncology, Queen Elizabeth Hospital, Hong Kong. The mean follow-up was 9.2 years. The stage distribution according to UICC/AJCC TNM staging was as follows: 58.6%, Stage I; 9.6%, Stage II; 26.1%, Stage III; 2.3%, Stage IV; and 3.4%, not stated. RESULTS: The 10-year cause-specific survival (CSS) rates were as follows: Stage I, 99.8%; Stage II, 91.8%; Stage III, 77.4%; and Stage IV, 37.1%. Multivariate analysis showed that the statistically significant poor prognostic factors for CSS were as follows: age older than 45, postoperative gross locoregional (LR) residual disease, distant metastasis (DM) at presentation, and lack of radioactive iodine (RAI) treatment. In patients with no DM and no postoperative LR disease, adjuvant RAI ablation reduced both LR failure (RR relative risk] = 0.29) and DM (RR = 0.2), although the CSS was not affected. In the subgroup of T1N0 M0 disease, no patient with RAI treatment had a relapse. External radiotherapy reduced the risk of LR failure to 0.35. Subgroup analysis revealed that external radiotherapy was particularly effective in increasing the probability of LR control of disease in patients with gross postoperative LR disease (RR = 0.36). CONCLUSIONS: Both RAI and external radiotherapy were effective treatment in PTC. Total or near-total thyroidectomy followed by RAI treatment appears to result in the best outcome. External radiotherapy to improve LR control is indicated in patients with gross postoperative residual disease. Treatment should be individualized for patients with T1N0 M0 disease.