Long-term exposure to inorganic arsenic is related to increased risk of cancer in the lung, skin, bladder, and, possibly, other sites. However, little is known about the consequences of developmental exposures in regard to cancer risk. During early summer in 1955, mass arsenic poisoning of infants occurred in the western part of Japan because of contaminated milk powder. Okayama Prefecture was most severely affected. We examined whether the affected birth cohorts in this prefecture experienced increased cancer mortality.

We targeted subjects who were born from September 1950 to August 1960 and died in Okayama Prefecture between January 1969 and March 2008 due to malignant neoplasm ( N = 3,141). We then compared cancer mortality (total, liver, pancreatic, lung, bladder/kidney, and hematopoietic cancers) between cohorts born before the milk poisoning (exposed group) and cohorts born after the poisoning (nonexposed group). We estimated mortality ratios and 95% confidence intervals.

Total and liver cancers were elevated in the cohort up to 1 year of age at time of the poisoning. In addition, pancreatic and hematopoietic cancers were elevated in the cohorts up to 5 years of age, and mortality ratios were approximately twice those of the nonexposed group. Increased risk of lung and bladder/kidney cancers was not apparent.

Although dilution is present in these cohort-based data, our study highlights the notion that developmental arsenic exposure may lead to a different pattern of cancer, including increases in pancreatic and hematopoietic cancer, as compared with adult or lifetime exposures to inorganic arsenic.