MON-552 Prognostic Impact of the Turin Criteria in Poorly Differentiated Thyroid Carcinoma

Abstract

Background Poorly differentiated thyroid carcinoma (PDTC) is morphologically and behaviorally intermediate between differentiated carcinoma and anaplastic carcinoma. The Turin criteria including solid, trabecular, and/or insular architecture, lack of typical nuclear features of papillary carcinoma, and mitoses, necrosis, or convoluted nuclei were adopted in the recent 4th edition of the World Health Organization (WHO) classification published in 2017. Materials and Methods Between 2006 and 2017, 11,001 cases underwent initial surgery for primary malignant thyroid tumor derived from follicular cells. A total of 75 (0.7%) cases were diagnosed with PDTC according to the 3rd WHO classification. Based on the Turin criteria (4th WHO classification), 30 (40%) cases were re-classified as PDTC-Turin (+), and 45 (60%) cases were PDTC-Turin (-). Clinicopathological features and prognosis were compared between PDTC-Turin (+) and PDTC-Turin (-). Result The 75 patients (48 females, 27 males) had a median age at the time of surgery of 57 years. The 5-year cause-specific survival (CSS) and disease-free survival (DFS) rates were 96.4% and 38.6% for PDTC-Turin (+), and 100% and 88.4% for PDTC-Turin (-), respectively. On univariate analysis, CSS and DFS rates were significantly worse in the PDTC-Turin (+) cases than in the PDTC-Turin (-) cases (log-rank test, p=0.005, and p=0.0004). Multivariate analysis showed that Turin criteria status was an independent prognostic factor for recurrence. Conclusion The prevalence of PDTC diagnosed with the Turin criteria was low, but it showed more aggressive behavior. The 4th WHO classification reflects the prognosis more accurately than the 3rd WHO classification.