Bilaterality as a Risk Factor for Recurrence in Papillary Thyroid Carcinoma

SIMPLE SUMMARY: About 30% of thyroid cancer is found on both thyroid lobes simultaneously. However, the prognostic effect of bilaterality remains unestablished and controversial. This study of 1258 patients demonstrated that patients with bilaterality were associated with a more aggressive disease. We also found that patients with bilateral thyroid cancer showed higher recurrence rates than those with unilateral tumors. Therefore, patients with bilateral thyroid cancer might require careful treatment and follow-up approaches. ABSTRACT: Previous studies suggested that the multifocality of papillary thyroid carcinoma (PTC) would increase the risk of recurrence; however, the impact of its bilaterality remains unclear. Between 2011 and 2018, 1258 patients with PTC underwent total thyroidectomy at Ewha University Medical Center. The 5-year recurrence-free survival rate was 95.7% in patients with bilateral PTC, while those with unilateral multifocal PTC and a unifocal tumor showed a 5-year event-free survival rate of 97.0% and 97.8%, respectively (p = 0.004). A multivariable Cox proportional hazards model indicated that bilaterality (HR 2.550, 95% CI 1.354–4.800), male sex (HR 2.010, 95% CI 1.007–4.013), and tumor size (HR 1.748, 95% CI 1.316–2.323) were associated with recurrence, although unilateral multifocality did not increase the risk of recurrence (HR 1.211, 95% CI 0.348–4.213). In conclusion, bilaterality was associated with aggressive features, including tumor size and microscopic ETE. Moreover, bilaterality was an independent predictor of recurrence in patients with PTC. Patients with bilateral PTC might require careful treatment and follow-up approaches.