Outcomes of Favorable-Stage, Well-Differentiated Thyroid Cancer with Microscopic Positive Margin

Abstract

A microscopic positive margin is an unfavorable prognostic factor for most cancers. However, the significance of a positive margin in favorable stage well-differentiated thyroid cancer (DTC) is controversial with little published data on the subject. This study reports outcome on a homogeneous study population where the positive margin question is most important for treatment decisions. Twenty-five consecutive patients treated between 2003 and 2013 at our institution met the following inclusion criteria: age > 18 years at time of I-131 treatment; DTC (papillary thyroid or follicular carcinoma with classic histology); confirmed microscopic positive margin; favorable stage (T1-3, N0-1b, M0); underwent total thyroidectomy +/- node dissection, and received I-131 treatment by the senior author of this study immediately after surgery at our institution. Median follow-up on surviving patients was 7.4 years (range, 3.2-12.8). Median I-131 treatment dose was 150 mCi with 92% receiving 150 or 200 mCi. The tumor recurrence rate was 24% and no patient was rendered tumor-free with additional treatment (surgery and/or repeat I-131 treatment). Only 1 patient died of thyroid cancer. Microscopic positive margin predicts a high recurrence rate following standard therapy in patients with otherwise favorable stage DTC. Current national guidelines recommend observation or low dose I-131 (30 mCi) for favorable stage patients. Our data suggests that more aggressive therapy is warranted in patients with a microscopic positive margin regardless of favorable stage category.