['Many factors gave been reported to be of prognostic importance for thyroid cancer. Biologic aggressiveness may influence postoperative recurrences and the prognosis of thyroid cancer. Immunohistochemical staining for the p53 protein and DNA content are novel factors that suggest biologic aggressiveness.', 'Retrospective study of the survival rate after operation of differentiated thyroid cancer was undertaken at Osaka Police Hospital. Age, gender operative method, extent of lymph node dissection, use of radioiodine, primary or recurrent tumor, tumor size and invasion, lymph node involvement, presence of distant metastases, DNA ploidy, percentage of S phase and G2M phase fractions, positive staining for the p53 protein, and histologic type and subtype were evaluated as possible prognostic factors by univariate and multivariate analyses of survival.', 'Positive staining for the p53 protein was related to postoperative local recurrence, and DNA ploidy was related to distant metastatic recurrence. Univariate analysis suggested that age, tumor size and invasion, lymph node involvement, presence of distant metastases, percentage of S phase fraction, histologic subtype, DNA ploidy, and positive staining for the p53 protein were significant prognostic factors. Multivariate analysis suggested that positive staining of the protein and DNA ploidy were independent prognostic factors for overall survival.'] Are overexpression of p53 protein and DNA content important biologic prognostic factors for thyroid cancer?