LAUSR

INTRODUCTION The impact of multifocality and bilaterality on recurrence in patients with low-risk, papillary thyroid cancer, is relevant when considering patients for a de-escalated treatment strategy: Hemithyroidectomy (HT) instead of total thyroidectomy followed by radioactive iodine (TT+/- RAI). This study aims to analyse contralateral tumor probability in patients treated for low-risk papillary thyroid cancer and assess multifocality and bilaterality as possible predictors for recurrence. METHODS Patients with low-risk papillary thyroid cancer treated with TT+/-RAI 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% (331/791) had multifocal disease, with 68.9% (228/331) of those cases being bilateral disease. The contralateral tumor probability after HT was 24.6% (150/610). for patients with unifocal disease and 43.1% (78/181) 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 pre-completion diagnosed unifocal disease 7.3% (11/150) had recurrent disease, while patients without contralateral disease after pre-completion diagnosed multifocal disease, 1.9% (2/103) had recurrence. Cox regression analysis showed that bilaterality (HR = 3.621;.95%CI=1.548-8.471) was the sole significant risk factor for recurrence. CONCLUSION Low recurrence rates are found in patients with either multifocal or bilateral disease in patients with low-risk papillary thyroid cancer. Bilaterality should be taken into account when considering these patients for de-escalated treatment strategy.