Paper PROJECTED LIFETIME CANCER RISKS FROM EXPOSURE TO REGIONAL RADIOACTIVE FALLOUT IN THE MARSHALL ISLANDS Charles E. Land,* André Bouville,* Iulian Apostoaei,' and Steven L. Simon* estimated by the National Cancer Institute in a more simplistic analysis conducted in 2004, these estimates of cancer risk are the best available as they are based on the most detailed dose reconstruction to date and comprehensively include populations at all locations and dose contributions from all nuclear tests. Health Phys. 99(2):201-215; 2010 Abstract—Radioactive fallout from nuclear test detonations during 1946-1958 at Bikini and Enewetak Atolls in the Marshall Islands (MI) exposed populationsliving elsewhere in the MI archipelago. A comprehensive analysis, presented in seven companion papers, has produced estimates of tissuespecific radiation absorbed dose to MI residents at all historically inhabited atolls from internal (ingested) and external irradiation resulting from exposure to radioactive fallout, by calendar year, and by age of the population at time of exposure. The present report deals, for the first time, with the implications of these doses for cancer risk among exposed members of the MI population. Radiation doses differed by geographic location and year of birth, and radiation-related cancer risk depends upon age at exposure and age at observation for risk. Using dose-response models based on committee reports published by the National Research Council and the National Institutes of Health, we project that, during the lifetimes of members of the MI population potentially exposed to ionizing radiation from weapons test fallout deposited during the testing period (1948-1958) and from residual radioactive sources during the subsequent 12 y (1959-1970), perhaps 1.6% (with 90% uncertainty range 0.4% to 3.4%) of all cancers might be attributable to fallout-related radiation exposures. By sub-population, the projected proportion of cancers attributable to radiation from fallout from all nuclear tests conducted in the Marshall Islands is 55% (28% to 69%) among 82 persons exposed in 1954 on Rongelap and Ailinginae, 10% (2.4% to 22%) for 157 persons exposed on Utrik, and 2.2% (0.5% to 4.8%) and 0.8% (0.2% to 1.8%), respectively, for the much larger populations exposed in mid-latitude locations including Kwajalein and in southern locations including Majuro. By cancer type, point estimates of attributable risk varied, by location, between 12% and 95% for thyroid cancer, between 2% and 78% for leukemia, and between 0.8% and 55% for all cancers combined. Thelargest projected risks pertain to the Rongelap Island community and the lowest risks pertain to the populations resident on the southern-mostatolls. While the projected cancer risks are smaller than those cer Key words: cancer; fallout; Marshall Islands; nuclear weapons INTRODUCTION PREVIOUSLY ADMINISTERED by Japan under a League of Nations mandate, the Marshall Islands (MI) archipelago was occupied by the United States (U.S.) during World War II. The group of atolls and islands was administered by the U.S. as a United Nations Trust Territory until 1986 when the Republic of the Marshall Islands (RMI) was established as a sovereign nation in free association with the U.S. After World WarII, the U.S. established the Pacific Proving Grounds, essentially the atolls of Bikini and Enewetak and the nearby ocean at the northwestern end of the archipelago, for testing nuclear weapons. The populations of Bikini and Enewetak were relocated to other atolls prior to testing. Between 1946 and 1958, 66 nuclear test detonations were carried out on or near to the atolls of the Marshall Islands. As discussed in four of the companion papers (Becket al. 2010; Bouville et al. 2010; Simon et al. 2010a and b), 20 of these tests resulted in varying levels of radiation exposure from radioactive fallout to residents of the inhabited islands in the archipelago. Significant exposures to radioactive fallout began in 1948, and exposures to residual fallout radioactivity continued after the cessation of testing in 1958, until about 1970. The highest exposures by far were from the * Division of Cancer Epidemiology and Genetics, National CanInstitute, National Institutes of Health, * SENES Oak Ridge, Inc., Oak Ridge, TN. Bethesda, MD; For correspondence contact: Steven L. Simon, National Cancer Institute, National Institutes of Health, 6120 Executive Blvd., Bethesda, MD 20892, or email at ssimon@mail.nih.gov. thermonuclear test (code name Castle Bravo) detonated on Bikini on | March 1954, which unexpectedly resulted in very substantial radiation exposure to 82 members of the Rongelap community who were on Rongelap Island and nearby Sifo Island (Ailinginae Atoll) and substantial (Manuscript accepted 5 March 2010) 0017-9078/10/0 Copyright © 2010 Health Physics Society DOI: 10.1097/HP.0b013e3 18 Ldc4e84 201