Are the clinical and pathological features of differentiated thyroid carcinoma really changed over the last 35 years? Study on 4187 patients from a single Italian institution to answer this question.

Background: In the last decades, a marked increased prevalence of differentiated thyroid cancer (DTC) has been observed worldwide. The aim of this study was to evaluate the changing features of DTC referred to our institution between 1969 and 2004.
Methods: Clinical and pathological features and prognostic factors were analyzed in 4187 DTC patients, subdivided into two groups: group 1 (n = 1215) and group 2 (n = 2972) diagnosed before and after 1990, respectively.
Results: Group 2 showed an increased proportion of micropapillary carcinoma and a concomitant decrease of follicular histotype. Male percentage was greater in group 2, whereas median age at diagnosis was unchanged. DTC of group 2 were more frequently associated with multinodular goiter or autoimmune thyroiditis, but many were unexpected findings. Features of aggressiveness were significantly less frequent in group 2, and the survival rate was greater (98.7 vs. 91.4%, P < 0.0001). Gender, age, histotype, tumor size, extrathyroidal macroinvasion, and lymph node and/or distant metastases were found to be poor prognostic factors in both groups using univariate analysis, but with multivariate analysis, only advanced age (odds ratio = 22.52 for older patients) and advanced stage (odds ratio = 53.54 for more advanced cases) were independently correlated with a lower survival.
Conclusions: DTC patients diagnosed after 1990 have smaller tumors with less advanced stage and a better prognosis. The question of whether this is related to the finding of tumors with a low clinical penetrance or to the anticipation of diagnosis remains to be clarified. Despite these significant differences, both advanced stage and older age still represent the most important poor prognostic factors for survival.