Microscopic positive margins in papillary thyroid cancer do not impact disease recurrence

The prognostic significance of microscopic positive margins in papillary thyroid carcinoma (PTC) remains unclear. The aim of this study was to determine if microscopic positive margins are associated with increased risk of disease recurrence.

This is a retrospective analysis of 610 patients with PTC using multivariate Cox regression to evaluate the association between microscopic positive margins and disease-free survival.

Microscopic positive margins were found in 67 (11%) patients and associated with extrathyroidal extension (P < 0.001), multifocality (P < 0.001), nodal metastases (P < 0.001), lymphovascular invasion (P < 0.001), age ≥55 years (P = 0.048), administration of radioactive iodine (RAI) therapy (P = 0.001) and a trend towards larger tumour size (18 versus 15 mm; P = 0.074). After a median follow-up of 3.4 years, there were 83 recurrences. Although involved margins were associated with increased risk of recurrence on univariate analysis (hazard ratio 2.6, 95% confidence interval 1.5-4.6; P = 0.001), there was no association after adjusting for age, nodal metastases, tumour size and extrathyroidal extension on multivariate analysis (hazard ratio 1.5, 95% confidence interval 0.8-2.9; P = 0.242). Similar results were obtained after adjusting for RAI and if margins were analysed as focal versus widely positive. In our study cohort, patients with involved margins generally had other indications for RAI. However, in the nine patients who did not receive RAI, there was no recurrence in the thyroid bed.

Despite a strong association between microscopic positive margins and other adverse prognostic factors in PTC, there is no independent association with disease recurrence on multivariate analysis. Microscopic positive margins are rare (1.1%) in the absence of other indications for RAI.