Poorly differentiated carcinomas of the thyroid with trabecular, insular, and solid patterns

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Abstract
BACKGROUND The term poorly differentiated (PD) carcinoma was proposed 20 years ago to define aggressive, follicular‐derived thyroid carcinomas with behavior intermediate between follicular/papillary and anaplastic carcinomas. Among the variable histologic patterns recognized in such tumors, trabecular‐insular‐solid (TIS) areas usually are predominant. Conversely, some authors pointed out that PD carcinomas are characterized by unequivocal, high‐grade histology with atypias, high mitotic counts, and necrosis rather than by a specific growth pattern. METHODS The clinicopathologic features of a series of 183 thyroid carcinomas with predominant (n = 165 tumors) or focal (n = 18 tumors) TIS growth patterns were studied by univariate and multivariate overall survival analyses and were compared with clinical outcomes. Subgroups included tumors with predominant oxyphilic features (n = 66 tumors) and (residual) papillary carcinoma features (n = 24 tumors). Control groups of papillary (n = 68 tumors), follicular (n = 71 tumors), and anaplastic (n = 35 tumors) carcinomas also were included for overall survival analysis. RESULTS TIS carcinomas had an intermediate behavior between papillary/follicular and anaplastic carcinomas (P < 0.0001). Univariate and multivariate statistical analyses demonstrated that age > 45 years (P = 0.007), the presence of necrosis (P < 0.0001), and a mitotic count > 3 per 10 high‐power fields (P = 0.01) were associated with poor outcome. A simplified scoring system based on statistically significant parameters allowed the identification of three prognostic subgroups (P < 0.0001). CONCLUSIONS PD TIS carcinomas overall followed a more aggressive course compared with differentiated thyroid carcinomas, irrespective of the extent of the TIS component. However, a numeric scoring system applied to specific clinicopathologic parameters further may identify three prognostic categories of patients who have significantly different survival rates at 5 years and 10 years. Cancer 2004;100:950–7. © 2004 American Cancer Society.