~ TABLE 2: Thyroid Nodules Diagnosed at Surgery through 1994 Adenomatous nodules Rongelap (67)* Ailingnae (19) Adenomas 18 Papillary cancers Follicular cancers Occult cancers 5 - - 4 t Utirik (167) 10 4 1° 6 Comparison (277)° 4 2 - 2° NOT INCLUDEDarethe following unoperated (and therefore unconfirmed) nodules: Rongelap --1: Ailingnae - 1: Utirik -- 1: Comparison-- 5. INCLUDEDare all consensus diagnoses of a panel of consultant pathologists: two differe t lesions were detected in one person from Rongelap, one from Ailingnae, and two from Utirik. a Numberof persons (including those in utero) who were originally exposed. b This numberincludesall persons who have been in the Comparison group since 1957. [Some have not been seen for many years; others were added as recently as 1976. No thyroid surgqries have been performedon this group since 1985. c Equally divided opinion in onecase; follicular carcinoma vs. atypical adenoma. d. Majority opinion in one case; occult papillary carcinomavs. follicular carcinoma. The s € patient had lymphocytic thyroiditis. characteristic of the type of thyroid injury sustained by the Marshallese. Two alternative explanations are 1) the "epidemic" of thyroid nodule formation is virtually over, and 2) the recent decrease in nodule incidence is due to random fluctuation and therefore temporary. Although time may tell which of the above explanations is correct, the respite in new cases provides an opportunity to bring together information on thyroid nodules collected by the Marshall Islands Medical Program over almost three decades and to draw tentative conclusions on several issues that may be relevant to inadvertent radiation exposures elsewhere. Radiation risks to the thyroid: One aspect of radiation-induced thyroid injury that has been repeatedly assessed is the dose of radiation required to induce it. Data available from the Marshall Islands Medical Program have been recently summarized (Robbins and Adams, 1988), with the following conclusions: 1) Therisk coefficient for thyroid nod s, adjusted for their occurrence in the omparison population, was 8.3 per 10° persons, er cGy, per year. 2) The risk coefficient for thyroid career was 1.5 per 10° persons, per cGy, per year. 3) The contribution of }311 to the thyrdid absorbed dose was relatively small, in the ringe of 1015%, the remainder being due taj short-lived radioiodines. Perhaps as a consequence, the radiation-induced risk for developfng nodular disease in the exposed Marshalld@se appears similar to that predicted if the total had been from externalirradiation lone. Since the above analysis included allfthe nodules up to the present, and since the Marshallese thyroid dose data have provided no insight int radiationinduced risk of thyroid carcinoma th&t was not already available from other sources,ino further comment on dose-response and riskf of thyroid disease will be made in this summary. 15