An impact of microscopic positive margin on incomplete response after I-131 treatment in differentiated thyroid cancer.

ABSTRACT

OBJECTIVE: To find an impact of microscopic positive margin on incomplete response after initial I-131 therapy in differentiated thyroid cancer. METHODS: We retrospectively recruited patients with differentiated thyroid cancer who underwent total thyroidectomy and received the first dose of radioiodine during January 2014-February 2018. Patients with grossly incomplete tumor resection or distant metastasis at the time of radioiodine therapy were excluded. Thyroid specimens were re-evaluated by one pathologist who was blinded to clinical information to determine microscopic margin status. Treatment response was evaluated at 6-12 months after therapy and was categorized according to the 2015 American Thyroid Association guidelines. Univariable and multivariable analyses were used to find an association between microscopic positive margin and incomplete response. RESULTS: A total of 101 patients (78 females; mean age 50.3 years) were enrolled. Ninety-four patients (93.1%) had papillary thyroid carcinoma. Microscopic positive margin was found in 27 patients (26.7%). After the median follow-up time of 10.3 months, incomplete response was observed in 13 patients (48.5%) and 17 patients (23.0%) with positive and negative margins, respectively. Multivariable analysis showed a significant association between microscopic positive margin and incomplete response after adjusting for tumor size, ETE, and cervical lymph node metastasis with adjusted odds ratio of 3.04 (95% CI 1.05-8.75, p value = 0.04). Moreover, after adding pre-ablative Tg as a covariate in 69 patients with negative TgAb, positive margin had a trend toward being associated with incomplete response with adjusted odds ratio of 3.43 (95% CI 0.73-16.07, p value = 0.118). CONCLUSIONS: Microscopic positive margin was found to be significantly associated with incomplete response after I-131 therapy in patients with differentiated thyroid cancer after adjusting for tumor size, ETE, and cervical lymph node metastasis and also had a trend toward being associated with incomplete response after adjusting for pre-ablative Tg.