Bilaterality, not multifocality, is an independent risk factor for recurrence in low-risk papillary thyroid cancer

Background The impact of multifocality and bilaterality on recurrence in patients with low-risk papillary thyroid cancer (PTC) is relevant when considering patients for a de-escalated treatment strategy: hemithyroidectomy instead of total thyroidectomy followed with or without radioactive iodine. This study aims to analyze contralateral tumor probability in patients treated for low-risk PTC and assess multifocality and bilaterality as possible predictors for recurrence. Methods Patients with low-risk PTC treated with total thyroidectomy followed with or without radioactive iodine in the Netherlands between 2005 and 2015 were included in this study. Patients were identified from the Netherlands Comprehensive Cancer Organization (IKNL) and linked with the nationwide network and registry of Pathology in the Netherlands (PALGA). Contralateral tumor probability and recurrence were assessed. Results Of 791 included patients, 41.8% (331 of 791) had multifocal disease, with 68.9% (228 of 331) of those patients having bilateral disease. The contralateral tumor probability after hemithyroidectomy was 24.6% (150 of 610) for patients with unifocal disease and 43.1% (78 of 181) for patients with multifocal disease. We found a higher trend of recurrence in patients with bilateral disease, regardless of multifocality: in patients with contralateral disease after precompletion diagnosed unifocal disease 7.3% (11 of 150) had recurrent disease, and patients without contralateral disease after precompletion diagnosed multifocal disease 1.9% (2 per 103) had recurrence. Cox regression analysis showed that bilaterality (hazard ratio = 3.621, 95% confidence interval = 1.548 to 8.471) was the sole statistically significant risk factor for recurrence. Conclusion Low recurrence rates are found in patients with either multifocal or bilateral disease with low-risk PTC. Bilaterality should be taken into account when considering these patients for de-escalated treatment strategy.