Thyroid Neoplasia in Marshall Islanders Exposed to Nuclear Fallout

Abstract

We studied the risk of thyroid neoplasia in Marshall Islanders exposed to radioiodines in nuclear fallout from the 1954 BRAVO thermonuclear test. We screened 7266 Marshall Islanders for thyroid nodules; the islanders were from 14 atolls, including several southern atolls, which were the source of the best available unexposed comparison group. Using a retrospective cohort design, we determined the prevalence of thyroid nodularity in a subgroup of 2273 persons who were alive in 1954 and who therefore were potentially exposed to fallout from the BRAVO test. For those 12 atolls previously thought to be unexposed to fallout, the prevalence of thyroid nodules ranged from 0.9% to 10.6%. Using the distance of each atoll from the test site as a proxy for the radiation dose to the thyroid gland, a weighted linear regression showed an inverse linear relationship between distance and the age-adjusted prevalence of thyroid nodules. Distance was the strongest single predictor in logistic regression analysis. A new absolute risk estimate was calculated to be 1100 excess cases/Gy/y/1 X 10(6) persons (11.0 excess cases/rad/y/1 million persons), 33% higher than previous estimates. We conclude that an excess of thyroid nodules was not limited only to the two northern atolls but extended throughout the northern atolls; this suggests a linear dose-response relationship.

The epidemiology of endocrine tumours.

“…There is a striking increase in the incidence of thyroid carcinoma (particularly papillary) in individuals exposed to ionising radiation, especially in the form of X-rays, either given therapeutically for other conditions (Hempelmann 1968) or by inadvertent exposure (Hamilton et al 1987). The risk is most evident in children and may have a prolonged lag phase of decades.…”

The cancer epidemiology of radiation

“…The number of Marshall Islanders who were heavily exposed was limited at around 250, but nine thyroid cancers were observed in this group over the following 32 years, although interpretation is complicated by the high occurrence of surgery and hormonal therapy (UNSCEAR, 1994;Howard et al, 1997). Broader studies of thyroid cancer in the Marshall Islands have found evidence of a general excess risk among the Marshall Islanders potentially exposed after the BRAVO test (Hamilton et al, 1987;Takahashi et al, 2003). A cohort study of around 2500 individuals exposed to radioiodine from the Nevada Test Site in the 1950s while attending schools in the general vicinity of the test site, and who were still resident in the area in the mid-1980s, found a marginally significant association (PB0.1) between thyroid cancer and assessed thyroid dose (Kerber et al, 1993).…”

Cancer risks in thyroid cancer patients

“…Data on risks associated with radioactive iodines are still relatively scarce despite studies of populations exposed to fallout from nuclear weapons testing (Conard, 1984;Hamilton et al, 1987) and patients receiving diagnostic (Holm et al, 1989) and therapeutic doses of '"'I (Brincker et al, 1973;Edmonds & Smith, 1986;Hoffman, 1984;Holm, 1984;Saenger et al, 1968). …”