Impact of Degree of Extrathyroidal Extension of Disease on Papillary Thyroid Cancer Outcome

Background: The clinical importance of extrathyroidal extension (ETE) on outcome of papillary thyroid cancer (PTC), particularly with respect to disease extending to the surgical margin is not well established. This study assessed the importance of surgical margin and extrathyroidal invasion relative to local control of disease and oncologic outcome. Methods: A retrospective analysis of a prospective institutional endocrine database was conducted on 276 patients with PTC treated between 1955 and 2004 to determine the impact of margin-negative resection (n=199, 72%), disease up to within 1mm of surgical margin (n=19, 7%), microscopic (n=39, 14%), and gross (n=19, 7%) ETE. Data were compared with Fisher's exact test or analysis of variance (ANOVA). Results: Median follow-up was 3.1-6.8 years per study group (disease-free survival, range 1-37 years). The proportion of those with age >45 years, prior radiation exposure, distant metastasis at presentation, and those undergoing total thyroidectomy was not significantly different between groups. Tumor size and multifocality correlated with extent of local disease, which in turn was significantly associated with regional nodal disease at time of primary operation as well as prevalence of persistence of disease after multimodality therapy. Extent of local disease correlated significantly with subsequent clinical recurrence after a disease-free period (p=0.006); however, recurrence rates were not significantly different between negative and close (1mm) margin resection. Conclusion: Oncological outcome correlates with the extent of extrathyroidal invasion. Outcome is worse in patients with gross extrathyroidal disease extension than in those with microscopic local invasion apparent on histopathological assessment. However, the risk of clinical recurrence appears similar between patients undergoing margin-negative and "close margin" resection.