Predictors of distant metastatic recurrence in intermediate-risk papillary thyroid carcinoma

Background: Patients with intermediate-risk papillary thyroid carcinoma (PTC) have a favorable prognosis with standard treatment of total thyroidectomy (TT) and adjuvant radioactive iodine therapy (RAIT). However, the benefits of TT or adjuvant RAIT remain undetermined, and they are often omitted in Japan. We investigated risk factors for life-threatening distant recurrence in patients with intermediate-risk PTC who are optimal candidates for adjuvant RAIT. Patients and Methods: Outcomes without RAIT were retrospectively examined in 4030 intermediate-risk conventional PTC cases underwent initial surgery from 2005 to 22 (IRB approval 20200709-1). Results: Lobectomy (LT) and TT was performed in 11.5% and 88.5%, respectively. Recurrent laryngeal nerve paralysis and hypoparathyroidism was less commonly observed in LT (1.3% and 0%) than TT (2.4% and 3.5 %). Fifty-six cases (1.4%) had distant recurrence. Recurrence-free survival rates at 10 years was 93.5%. There was no significant difference in recurrence rate between LT and TT. Age >= 55, cN1b, and tumor diameter >30 mm significantly associated with distant recurrence. There was a strong relationship between the number of positive risk factors and recurrence; the distant recurrence rate in cases of 0, 1, 2, and 3 positive factors was 0.3% (4/1203), 1.3% (25/1889), 2.7% (23/830) and 7.1% (4/52) (HR 6.46 (2.34-17.86), Log-rank <0.001). Conclusion: For intermediate-risk conventional PTC, there is no difference in prognosis even if LT was selectively conducted. However, in patients with risk factors for distant metastatic recurrence, such as age >= 55 years, cN1b, and tumor size >30 mm, adjuvant RAIT was considered eligible.