The study of late low dose effect to thyroid disease in Marshall Islands

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The results from the examination in 1994 and 1996 at Kwajalein and Majuro in Marshall Islands were as follows ;1. The prevalence of palpable thyroid nodules had reverse correlation to the angle rhetafrom Bikini. 2. The prevalence of hypothyroidism and the ratio of positive auto-antibody to thyroid were quite lower than Japanese adults and Nagasaki atomic bomb victims. 3. On the basis of WHO criteria on iodine deficiency, one third of Majuro residents were estimated as moderate iodine deficiency. 4. The radiation dosimetry for the Marshall people during atomic bomb testing era (1949-58) could not be completed. 5. The mutation of codon 61, K-ras oncogene was not detected in 70 fine needle aspiration biopsy specimens. 6. In eleven operated thyroid in 1994 at Majuro, seven papillary carcinomas and three carcinomas were pathologicaly diagnosed. The p53 protein was immunohistochemically positive in four cases.Since no dosimetry data was available for this time, we could not have definite conclusions on the object. But some suggestions were given from the above results. 1. From the geographical distribution of the prevalence of thyroid nodule, there was possibility of low dose radiation effect of atomic bomb testing. 2. Rather poor iodine intake might affect the thyroid nodule prevalence. 3. The high ratio of follicular carcinoma was contradictory to other reports on the thyroid cancer induced by radiation. 4. In Chernobyl the mutation of codon 61, K-ras was frequently detected, but none in Marshall Islands. The cause of the thyroid tumors in Marshall Islands might be different from that in the Chernobyl area.