Abstract 5178: Multifocality is an independent predictor of regional lymph node metastasis in Middle Eastern papillary thyroid carcinoma
Authors: Poyil Pratheeshkumar , Siraj Abdul K , Parvathareddy Sandeep Kumar , Padmaja Divya , Thangavel Saravanan , Begum Rafia , Diaz Roxanne , Al-Obaisi Khadija , Al-Kuraya Khawla S. 
Published: June 2022

Abstract
Background: Papillary thyroid carcinoma (PTC) is treatable, with favorable prognosis and very low disease-specific mortality. However, PTC recurrence is relatively common in loco-regional and distant sites. Although multifocality is a common occurrence in PTC, its prognostic impact remains controversial. In addition, data on prevalence and prognostic significance of multifocality in PTC from Middle Eastern ethnicity is unknown. Therefore, the aim of this study was to investigate the prognostic value of multifocality in PTC larger than 1cm and papillary thyroid microcarcinoma (PTMC) in our center.
Methods: A cohort of 1515 patients who underwent total thyroidectomy were retrospectively reviewed. Aggressive histopathologic variants of PTC were excluded to avoid their potential confounding effect on clinical outcomes. We identified 1087 patients who had PTC with primary tumor exceeding 1cm and 150 patients with PTMC, with medium follow up of 9.2 years. In each group, we compared patients with unifocal and multifocal disease. Clinico-pathological and molecular correlations were analyzed. Logistic regression analysis was used to assess the relation between multifocal tumors and lymph node metastasis.
Results: The incidence of multifocality in PTC larger than 1cm was 48.3% (525/1087), whereas it was 38.7% (58/150) in PTMCs. In patients with PTC &gt; 1cm, multifocality was significantly associated with aggressive markers such as extrathyroidal extension (p &lt; 0.0001), lymphovascular invasion (p = 0.0047), lymph node (LN) metastasis (p = 0.0006), distant metastasis (p = 0.0305) and BRAF mutation (p = 0.0113). In analogous analysis of patients with PTMC, multifocality was significantly associated with extrathyroidal extension (p &lt; 0.0001), LN metastasis (p = 0.0005) and BRAF mutation (p = 0.0006). In both sub-groups, disease recurrence and overall survival did not differ between unifocal and multifocal group. Multivariate analysis showed that multifocality was an independent predictor of LN metastasis (Odds ratio (OR) = 1.31; 95% confidence interval (CI) = 1.00 - 1.71; p = 0.0472 for PTC &gt; 1cm and OR = 1.88; 95% CI = 1.00 - 3.54; p = 0.0491 for PTMC).
Conclusions: Tumor multifocality is frequently observed in Middle Eastern PTC and PTMC and is a predictive factor for LN metastasis in PTC. Given the predictive value of multifocality in Middle Eastern ethnicity, aggressive therapy and intensive follow-up should be considered for both PTC and PTMC with multifocality. Regional LN metastasis should be closely monitored and prophylactic central lymph node dissection could be considered in these patients.
Citation Format: Pratheeshkumar Poyil, Abdul K Siraj, Sandeep Kumar Parvathareddy, Divya Padmaja, Saravanan Thangavel, Rafia Begum, Roxanne Diaz, Khadija Al-Obaisi, Khawla S. Al-Kuraya. Multifocality is an independent predictor of regional lymph node metastasis in Middle Eastern papillary thyroid carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5178.