In addition, eight cases with an unknown RET/PTC rearrangement and three cases with the concomitant expression of RET/PTC1 and RET/PTC3 were found.     ///    "Conflicting results on the frequency and type of RET/PTC rearrangements have been reported in relation to age, radiation exposure, and histological tumor variant. "    ///    "No significant correlation was observed between the frequency and/or the type of RET/PTC rearrangement and clinical-epidemiological features of the patients such as age at diagnosis, age at exposure, histological variant, gender and tumor-node-metastasis (TNM) categories. "    ///    The overall frequency of RET/PTC rearrangements in papillary thyroid cancer was 55%.     ///    "RET/PTC rearrangements were also found in 52.4% of post-Chernobyl benign nodules, in 37.5% of benign nodules exposed to external radiation and in 13.9% of naturally occurring nodules (P = 0.005, between benign post-Chernobyl nodules and naturally occurring nodules). "    ///    "No difference of RET/PTC rearrangements was found between samples from irradiated (external x-ray) or not irradiated adult patients, as well as between children and adults with naturally occurring, not irradiated, thyroid cancer. "    ///    "RET/PTC rearrangements in thyroid nodules: studies in irradiated and not irradiated, malignant and benign thyroid lesions in children and adults.. "    ///    "In conclusion, our results indicate that the presence of RET/PTC rearrangements in thyroid tumors is not restricted to the malignant phenotype, is not higher in radiation-induced tumors compared with those naturally occurring, is not different after exposure to radioiodine or external radiation, and is not dependent from young age. "    ///    The relative frequency of RET/PTC1 and RET/PTC3 in rearranged benign tumors showed no major difference.     ///    "We designed the present study to evaluate in a single laboratory, using the same methodologies, the pattern of RET/PTC activation in thyroid tumors from different groups of patients (exposed or not exposed to radiation, children or adults, with benign or malignant tumors) in relationship to the above mentioned variables. "