Early-Life Exposure to DDT from Indoor Residual Spraying and Adult Risk of Reproductive Cancers: A Nationwide Study...

Background: Early-life exposure to dichlorodiphenyltrichloroethane (DDT) may increase adult cancer risk, but evidence from Asian populations remains limited. Taiwan's nationwide indoor residual spraying (IRS) program during the 1950s provides a unique setting to examine long-term reproductive cancer risk associated with early-life DDT exposure. Methods: We conducted an ecological study using township-level DDT IRS frequency (0-5 times) as the exposure indicator. Individuals born between 1952 and 1958 were followed from 1979 to 2022 for incident reproductive cancers based on data from the Taiwan Cancer Registry. Poisson regression models were applied to estimate relative risks associated with each additional IRS exposure. Results: A total of 109,244 reproductive cancer cases were identified. Each additional DDT spraying round was associated with increased risks of breast, ovarian, corpus uteri, prostate, testicular, and cervical cancers (RRs = 1.01-1.16). Elevated risks were observed for testicular cancer (RR = 1.16, 95% CI: 1.01-1.23) and cervical cancer (RR = 1.01, 95% CI: 1.002-1.02), for which Asian epidemiological evidence remains limited. Higher exposure levels were also associated with differences in stage at diagnosis for breast cancer among women aged ≥55 years and for corpus uteri cancer. Conclusions: Early-life DDT exposure was associated with increased risks of several reproductive cancers. These findings support the Developmental Origins of Health and Disease framework and suggest that environmental exposures during critical developmental windows may influence long-term cancer risk. However, the findings should be interpreted cautiously given the ecological study design and potential residual confounding.