Poorly differentiated thyroid carcinoma and poorly differentiated area in differentiated thyroid carcinoma: is there any difference?

PurposePoorly differentiated thyroid carcinoma (PDTC) patients have worse outcomes than patients with differentiated thyroid carcinoma (DTC), but the implication of poorly differentiated areas (PDAs) noted in DTC is not very well understood. The aim of the present study was to compare the clinicopathologic profiles and outcomes of PDTC and DTC with PDA.MethodsA total of 142 patients, managed at out center between September 1989 and June 2016, were enrolled in this retrospective study. Histology was reviewed, and the patients were divided in the following three groups: poorly differentiated carcinoma [PDTC; group 1 (n=27)]; papillary thyroid carcinoma with PDA [PTC with PDA; group 2 (n=27)]; and follicular thyroid carcinoma with PDA [FTC with PDA; group 3 (n=88)]. Clinico-pathologic profiles and outcomes were compared between the three groups. The Kaplan-Meier method was used for survival analysis. The log-rank test and Cox regression model were used to perform univariate and multivariate analyses of the factors affecting the overall survival (OS).ResultsThe clinical profiles of the three groups were comparable except for significantly less incidence of lymph node involvement (p=0.002) and extra-thyroidal invasion (p=0.002) and higher incidence of distant metastases (p=0.01) in group 3. Median follow-up period was 47.5months, and 5- and 10-year OS were 57 and 14%, respectively. There was no difference between OS of PDTC and DTC (group 2+3), but group 3 patients had significantly better OS than group 2 patients. Univariate analysis revealed that tumor size (p=0.04), extra-thyroidal invasion (p=0.05), lateral compartment lymphadenopathy (p=0.002), distant metastases (p=<0.001), absence of encapsulation (p=0.03), and >75% PDA (p=0.001) were associated with worse OS. Multivariate analysis revealed tumor size (p=0.005), distant metastases (p=0.012), lymphadenopathy (p=0.017), TNM staging (p=<0.001), and PDA>75% (p=<0.001) to be significantly associated with OS.ConclusionThere is no difference in the outcomes of PDTC and DTC with PDA. However, PTC patients with PDA have worse outcomes than FTC patients with PDA. Irrespective of tumor type, the presence of more than 75% PDA in DTC is associated with adverse outcomes.