Background: The implication of microscopic positive margin status in resected papillary thyroid cancer (PTC) is poorly-understood, whereas serum thyroglobulin levels (Tg) are used routinely after total thyroidectomy in PTC as a potential surrogate for early disease recurrence. The aim of this study was to determine whether stimulated Tg is a predictor of structural recurrence in patients with microscopic positive margins in PTC.
Methods: This retrospective cohort study reviewed 468 patients who underwent total thyroidectomy +/- central lymph node dissection for PTC >10mm in the period 1985-2016. Exclusion criteria were; metastatic disease, gross residual disease at resection and absence of a post-operative Tg measurement between 3-52 weeks post-operatively. The median follow-up time was 2 years (range; 1-19 years). The primary outcome measure was structural recurrence, defined as disease detected on imaging modalities (including ultrasound, computed tomography or positron emission tomography) and confirmed on biopsy.
Results: The median patient age was 49 years (range 20-87). There were 355 females (75.9%). The overall structural recurrence rate was 13.0%. Three hundred and forty-seven patients had uninvolved margins at time of resection with a structural recurrence rate of 11.5% and one hundred and twenty-one patients had microscopic positive margins with structural recurrence rate of 17.4% (p=0.101). In patients with microscopic positive margins, there was a significant difference (p=0.0007) in the rate of structural recurrence between patients with early post-operative Tg<2ng/mL (5.2%) compared to patients with Tg≥2ng/mL (28.6%). Univariate analysis identified lymph node involvement, vascular invasion and early Tg as significant predictors of recurrence. After multivariate analysis, early serum Tg remained the only significant predictor of recurrence.
Conclusion: In patients undergoing total thyroidectomy for papillary thyroid cancer with known microscopic margin involvement, early post-operative stimulated Tg can be used to accurately quantify the risk of disease recurrence.