Radiation doses and cancerrisks in the Marshall Islands @ S. L. Simon ET AL. the doses from acute intakes. However, doses from chronic intakes were small and refinements to the esti- mation of the uncertainty associated with them would contribute little to the overall dose uncertainty. Projected cancer risks The annual doses from external irradiation and from internal irradiation that were estimated for the 25 Marshallese population groups according to birth year were combined with the population sizes and with agedependent organ-specific risk coefficients to derive the corresponding cancerrisk projections presented in Land et al. (2010). Risk estimates were presented in terms of the number of cancers by organ site projected to occur among Marshallese as a consequence of exposure to fallout from regional nuclear tests. The cancer risks were based on an estimated population of 12,175 residents of the Marshall Islands born before 1948 and another 12,608 born in the years 1948 through 1970, giving a total potentially exposed population of 24,783. Projected lifetime numbers of baseline and radiation-related (ex- cess) cancers are shown in Table 10 by cancer type: occurred or will occur and that can be attributed to exposure to radioactive fallout, expressed as a percentage, is about 20% for thyroid and about 5% for leukemia. These percentages can be comparedto all other cancers, for which the attributable fractions are on the order of 1%. The attributable fractions, as expected, were much higher among the most heavily exposed population groups (Landet al. 2010). A breakdown of the estimated number of cancer attributable to exposure to fallout radiation according to population group and time period, as well as estimation of the uncertainties in the projected numberof cancers, is discussed in detail by Land etal. (2010). The attributable fractions (%) of all cancers from exposure to fallout radiation within each of the four atoll groups with 90% uncertainty ranges are presented in Table 11 and have the same geographic pattern as for 'S"Cs deposition illustrated in Fig. 2. Because of the small numbers of projected cases on someatolls (resulting in highly uncertain estimates), the cancer risk projections are shown only for groups of atolls rather than for individual atolls. leukemia, thyroid, stomach, and colon. In addition, the numbersof “all other solid cancers” has been estimated using the colon dose as representative of the dose to most other organs and tissues of the body. The projected number of baseline (non-radiation related) cancers among the 24,783 Marshallese in all organs totals 10,600, while the projected numberof excess (radiationrelated) cancers is 170, including 65 that have yet to occur (Land et al. 2010). In comparison to our 2004 estimates, which also are presented in Table 10, the numbers of projected radiation-related thyroid and colon cancers are much smaller as a result of a much more realistic dose assessment. Whenthe entire population of the Marshall Islands is considered, the estimated fraction of cancers that has 121 CONCLUSIONS The methods and findings described in this paper and the seven companion papers represent the most comprehensive retrospective evaluation ever conducted of exposure of Marshallese and the related cancer risks from regional nuclear testing. This effort, in response to a Congressional request, will provide information useful to U.S. Congressional committees as well as to health authorities both in the U.S. and in the Marshall Islands. However, the methods are also illustrative of methods that may be useful in broader circumstances, some of which might occur in the future. Though nuclear testing in the atmosphere is not likely to be revived, nuclear detonations that would result in exposure of the public Table 10. Projected numberoflifetime baseline and excess cancers for the entire population of the Marshall Islands by cancer type and comparison with the results of the NCI preliminary study (DCEG 2004). This study (Landet al. 2010) Preliminary study (DCEG 2004) Cancer type Leukemia Thyroid Stomach Colon Baseline number of cancers* 123 127 326 470 Excess number of cancers Total number of cancers 5 262 15 157 128 389 341 627 Baseline number of cancers* 140 190 570 930 Projected Projected excess number excess number of cancers of cancers from 2009 1948-2008 onwards 6.0 35 3.1 7.2 1.4 15 3.6 9.3 Rounded total number of cancers 147 240 577 946 All other solid cancers 4,550 93 4,643 8,800 54 36 8,890 Rounded total number of 5,600 530 6,100 10,600 105 65 10,800 cancers “The 2004 preliminary analysis assumed the population size obtained by the 1958 census, while the present study is based upon the total number of people exposed anytime between 1948 and 1970, which is projected to be about twice the size of the 1958 population.