Multivariate study of prognostic factors for differentiated thyroid carcinoma: the significance of histologic subtype.

We re-examined 239 patients with differentiated thyroid carcinoma (222 with papillary carcinoma and 17 with follicular carcinoma) especially for the clinico-pathologic entity of poorly differentiated carcinoma, and made univariate and multivariate analyses of the results to evaluate whether it would be of value in estimating the prognosis in thyroid cancer patients. In the univariate study, no significant difference was found in either survival and disease-free survival between papillary and follicular carcinomas, but between well differentiated and poorly differentiated carcinomas. In the multivariate study, however, the presence of poorly differentiated carcinoma did not appear to be an unfavorable prognostic factor. The sex, tumor size, and presence of distant metastases or grossly malignant residue in the neck after operation were, on the other hand, confirmed by the analyses to be important prognostic factors. We concluded that histologic subclassification may be less useful in estimating the prognosis in patients with differentiated thyroid carcinoma than other factors such as sex and the extent of the tumor.