Prognostic significance of histologic grading compared with subclassification of papillary thyroid carcinoma

BACKGROUND, Papillary thyroid carcinomas represent a diversity of morpholog ic subtypes and variants, but to the authors' knowledge the prognostic sign ificance of subclassification is not clear. Therefore, the authors compared the value of histologic classification with a combined assessment of histo logic key features such as marked nuclear atypia, tumor necrosis, and Vascu lar invasion (i.e., histologic grade). METHODS. One hundred twenty-eight surgically treated patients with papillar y carcinoma > 10 mm were studied. The tumors were subclassified and individ ual histologic features were examined and compared in univariate and multiv ariate survival analyses. RESULTS. Of all the cases, 55% were of the usual type, whereas 27% showed c omplex histologic features with different components present and 18% repres ented specific subtypes. Tall cell differentiation showed an increased freq uency of tumor necrosis and vascular invasion, and tumors with solid areas had an increased occurrence of mitotic figures and Vascular invasion. Patie nts with tall cell tumors tended to have reduced survival (P = 0.074), and two patients with columnar cell features died of the disease. When combined , the group of patients with ail tumor subtypes had significantly reduced s urvival when compared with the remainder of patients (P = 0.034), although the difference was only minor. Histologic grade was highly significant (P = 0.0001) in survival analysis, together with mitotic frequency (P = 0.028), S-phase (P = 0.015), and G(2)M-phase fractions (P = 0.040). In multivariat e analysis, tumor dimension CP = 0.019) and histologic grade (P = 0.008] sh owed significant and independent prognostic importance, whereas subclassifi cation was not: found to be significant. CONCLUSIONS. Subclassification of papillary thyroid carcinomas had only a m inor prognostic impact, whereas histologic grade was a strong and independe nt prognostic marker. The authors recommend that all papillary carcinomas b e given a histologic grade based on a combined examination of nuclear atypi a, tumor necrosis, and vascular invasion. [See editorial on pages 1766-68, this issue J Canter 2000;88:1902-8. (C) 2000 American Cancer Society.