['RET proto-oncogene rearrangements (RET/PTC) are causative events in the pathogenesis of a subset of papillary thyroid cancer (PTC). The prevalence of RET/PTC varies in different countries and according to specific clinical features: it is higher after radiation exposure and it is claimed to be higher in young patients. Conflicting results are reported regarding the prognostic role of RET/PTC activation.', 'To investigate the prognostic meaning of RET/PTC rearrangement on the long term outcome of PTC.', "We have studied the expression of the RET encoded protein in 127 papillary thyroid carcinomas by immunohistochemistry using a polyclonal antibody against the tyrosine-kinase domain of the RET protein. These cases have been collected during 1970-1985, and have a mean (+/-S.D.) period of follow-up of 18.6+/-3.7 years (range 12-27 years). The results have been compared with the patients' outcome.", "The tyrosine-kinase domain of RET was expressed in 82 (64.6%) papillary carcinomas. Among them, RET was highly expressed in 65 (51.2%) cases and moderately expressed in 17 (13.4%). RET expression was absent in 45 (35.4%) cases. No correlation was found between RET expression and other parameters such as sex, age at diagnosis, tumor class and histological variant. Follow-up analysis showed no influence of RET expression on patients' outcome. By multivariate analysis, age (>45 years) and tumor class IV, but not sex and RET expression were adverse prognostic indicators of death."] Does rET protein expression have no prognostic impact on the long-term outcome of papillary thyroid carcinoma?