• So Young Park, Hye In Kim, Joon Young Choi, Jun-Ho Choe, Jung-Han Kim, Jee Soo Kim, Young Lyun Oh, Soo Yeon Hahn, Jung Hee Shin, Soo Hyun Ahn, Kyunga Kim, Jong Gill Jeong, Sun Wook Kim, Jae Hoon Chung, and Tae Hyuk Kim.
• Division of Endocrinology and Metabolism, Department of Medicine, Thyroid Center, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Republic of Korea.
• Oral Oncol. 2018 Sep 1; 84: 41-45.

ObjectivesThe efficacy of radioiodine remnant ablation (RRA) for patients with differentiated thyroid carcinoma (DTC) with gross extrathyroidal extension (ETE) is well described in observational studies. However, its role in gross ETE invading only strap muscles, T3b category in the newly proposed eighth edition of the TNM staging system, is currently unknown.MethodsThis study retrospectively analyzed 260 DTC patients with ETE invading only strap muscles who underwent thyroidectomy at a tertiary Korean hospital between 1994 and 2005. Cancer-specific survival (CSS) and recurrence-free survival (RFS) in the no RRA (n = 13), low RRA activity (<3.7 GBq, n = 80), and high RRA activity (≥3.7 GBq, n = 167) groups were studied.ResultsNo significant differences were observed between low and high activity RRA groups in terms of 10-year CSS (97.3% versus 99.3%; HR 0.23, 95% CI 0.02-2.57; p = .235) and RFS (86.8% versus 88.8%; 0.90, 0.40-2.03; p = .804). In the no RRA group, no patients died of cancer, and only one developed structural recurrence. In Cox regression analyses with inverse probability of treatment weighting adjusted for clinicopathologic risk factors, high activity RRA was not related to recurrence outcomes compared to low activity (HR 0.60, 95% CI 0.26-1.35; p = .214).ConclusionsLong term oncologic outcomes did not significantly differ between low versus high activity RRA groups, which suggests that low activity RRA might be sufficient in patients with DTC with gross ETE invading only strap muscles. Further studies are needed to clarify the optimal activity of RRA in these patients.Copyright © 2018 Elsevier Ltd. All rights reserved.

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