Lymph-node ratio for micropapillary and nonmicropapillary differentiated thyroid cancers: a comprehensive analysis

Background: Regional lymph-node metastasis plays a pivotal role in predicting recurrence in patients with differentiated thyroid cancer (DTC). Recent studies have highlighted the prognostic potential of the lymph-node ratio (LNR). This research aims to discern and compare LNR values in patients who underwent neck dissection specifically for micropapillary DTC and those with nonmicropapillary DTC. Methods: Patients who underwent central lymph-node dissection (CND) due to DTC at three different tertiary centers in Istanbul between 2013 and 2023 were retrospectively reviewed. Patient and tumor characteristics (age, sex, type of neck dissection, multifocality, subtype of DTC, and LNR) were recorded and analyzed. The total harvested lymph-node (LN) number, metastatic LN number, and LNR were recorded and compared between the micropapillary and nonmicropapillary groups. Results: The mean age of the patients was 44 ± 13.1 years, and the F/M ratio was 290/75. The mean dominant nodule size measured 15.53 ± 0.63 mm. Neck dissection procedures were unilateral CND in 62% (n = 226) and bilateral CND in 38% (n = 139). According to the histopathological examination results, nonmicropapillary thyroid carcinoma (non-PTMC) was detected in 220 patients (60%), whereas papillary thyroid microcarcinoma (PTMC) was detected in 145 patients (40%). The mean LNR was 0.14 ± 0.2 in patients with PTMC and 0.17 ± 0.2 in patients with non-PTMC (p = 0.286). Conclusion: This study demonstrated that when regional lymph-node metastases (LNMs) develop in patients with PTMC, the LNR can be as high as that in patients with PTC. These findings emphasize that, in clinical assessments of PTC, the LNR is independent of the main tumor size.