Influence of cellular DNA content on survival in differentiated thyroid cancer

Cellular DNA content was measured using a novel flow cytometric method to analyze paraffin-embedded tissue blocks from 125 patients with differentiated thyroid cancer. DNA aneuploidy was found in 20 (24%) of the 82 papillary, 20 (56%) of the 36 follicular, and in four (57%) of the seven medullary carcinomas. Aneuploidy was found to be more common in the elderly (P less than 0.002), in moderately and poorly differentiated carcinomas (P less than 0.004), and in tumors infiltrating beyond the thyroid capsule (P less than 0.03). Patients with an aneuploid tumor had less favorable cumulative survival (P less than 0.0001) than patients with diploid cancer. However, in papillary and follicular carcinomas, multivariate analysis using stepwise Cox model showed age at diagnosis, follicular type, and tumor invasion beyond the thyroid capsule to be more important independent prognostic factors. Increasing probability of DNA aneuploidy with increasing age explains partially why prognosis of differentiated thyroid carcinoma is poor in older patients.