CHILDHOOD THYROID-CANCER - COMPARISON OF JAPAN AND BYELARUS

The high incidence of childhood thyroid cancer in Belarus is suspected to be due to radiation exposure after the Chernobyl reactor accident. To clarify the clinical and histological characteristics of childhood thyroid cancer in Belarus, we therefore compared these patients to a radiation non-exposed control series in Japan. In Belarus, 26 thyroid cancers in subjects aged 15 or younger were diagnosed among 25,000 scr eened between 1991 and 1995 by Chernobyl-Sasakawa Health and Medical C ooperation Project. The clinical and morphologic features of these 26 cases were compared to 37 childhood thyroid cancers in Japan diagnosed between 1962 and 1995. The age distribution at operation in Belarus s howed a peak at 10 years old, with a subsequent fall in numbers. In co ntrast, the age distribution at operation in Japan showed a smooth inc rease between the ages of 8 and 14. The mean tumor diameter was smalle r in Belarus than that in Japan (1.4 +/- 0.7 vs. 4.1 +/- 1.7 cm, P<0.0 01). The sex ratio, regional lymph node metastasis, extension to surro unding tissues or lung metastasis did not differ significantly. Histol ogically, all cases in Belarus were papillary and in Japan 33 cases we re papillary and 4 cases were follicular carcinomas. Among papillary c arcinomas, the frequency of a solid growth pattern, a criteria for cla ssifying a tumor as poorly differentiated, was higher in Belarus than that in Japan (61.5 vs. 18.2%, P<0.001). The difference between the fe atures of childhood thyroid cancer in Japan and Belarus may be due to the difference in the process of carcinogenesis, but more direct evide nce and further analysis by molecular epidemiology are needed in Belar ussian cases.