Morphology of thyroid carcinoma in children and adolescents of the Russian Federation: analysis for the 20 years period after the Chernobyl accident

Full text: A dramatic increase in the number of childhood thyroid carcinoma cases reported four years after the Chernobyl accident has attracted a rapt attention of the world scientific community (K. Baverstock et al., 1992; V. Kazakov et al., 1992; E. Ron et al., 1992; D. Williams et al., 1993). Twenty years after the accident, a considerable experience of the studies in post-Chernobyl thyroid cancer has been acquired and summarized in a number of journal publications and monographs. The purpose of the current study was an analysis of morphological features of thyroid carcinoma in children and adolescents of the Russian Federation (RF) exposed to radiation after the accident. Material of thyroid tumors examined at the Department of Pathology of the Medical Radiological Research Center of Russian Academy of Medical Sciences (MRRC RAMS) was available as post-operational specimens removed during the surgical treatment at MRRC RAMS, specimens sent to MRRC RAMS for consultative review and those collected from other hospitals in frame of joint research projects. The analysis includes 571 thyroid carcinoma cases diagnosed in children and adolescents ages 0-20 at the time of the accident (556) and in children born after the accident (15). There were 386 cases from patients residents of the most radio contaminated areas of RF: Bryansk (209), Kaluga (57), Oryol (52), Tula (68), and 185 cases from patients from other less contaminated and relatively 'clean' territories. Papillary carcinoma was the most common histological type of thyroid carcinoma (88,6%). Other tumor types were registered significantly rare: follicular carcinoma in 6,1%, medullary carcinoma in 3,7%, thyroid carcinoma not otherwise specified in 1,4%, and undifferentiated carcinoma in 0,2%. Papillary cancer was non-homogeneous in its predominant growth pattern. It was divided into specific subtypes: classic papillary (39.5%), follicular variant (38,3%), solid variant (16,3%), papillary microcarcinoma (3.5%), diffuse sclerosis variant (1,2%), and other variants (1,2%). Prevalence of the classic papillary variant was increased and that of solid variant decreased in patients of advanced age. Frequency of the papillary variant was also increased in patients with a longer latent period (time between accident and diagnosis). No morphological distinctive features of thyroid carcinoma were revealed in children and adolescents living on the territories with different levels of radio contamination, iodine deficiency and depending on individually reconstructed doses of thyroid exposure. Morphology of papillary carcinoma in children born after the accident was similar to that observed in children of young age group (5-14 at the time of diagnosis) who had been born before the accident. These tumors were predominantly solid in architecture, non-encapsulated with morphological evidence of aggressive growth (invasion into adjacent thyroid, thyroid capsule and extra-glandular spreads). Reasons of the thyroid carcinoma cases development in children born after the accident are not yet completely understood. Further studies employing modern morphological and molecular techniques are needed to reveal specific markers of radiation induced and 'spontaneous' thyroid cancer. Creation of the Russian and International thyroid tissue bank where tumor samples from patients exposed after the accident are collected should contribute to the progress in the field