Kidney cancer risk among indium-exposed workers: a multicenter cohort study.

[OBJECTIVES] To describe the characteristics of incident cases and calculate the standardized incidence ratio (SIR) of kidney cancer in a multicenter cohort study.

[METHODS] Baseline studies included 601 individuals across 12 factories manufacturing or recycling indium compounds between 2003 and 2006. In total, 341 individuals had undergone at least 1 follow-up health checkup by 2022. Of these, 128 individuals were examined from 2019 to 2022, with a mean follow-up duration of 17.1 years (range 13.3-18.4). The overall SIRs of kidney cancer were calculated.

[RESULTS] One female and 2 male incident cases of kidney cancer were identified at 3 different factories. The mean age was 55 years, and they were either smokers or secondhand smokers. The mean duration of indium exposure was 14.6 years, and the mean serum indium concentration at baseline was 2.3 μg/L (range <0.1-4.3 μg/L). One case consistently exhibited undetectable indium concentrations in both serum and kidney tissue. Another case involved double primary cancers of the lung and kidney. The expected number of kidney cancer cases based on the Japanese general population was 0.505. The overall SIR was 5.95 (95% CI, 2.02-17.47). Even after excluding the case with undetectable In-S and In-K levels, the overall and female SIRs remained significantly elevated (overall SIR 3.96; 95% CI, 1.09-14.44; female SIR 56.86; 95% CI, 9.80-314.69).

[CONCLUSIONS] Indium exposure may contribute to the development of not only lung cancer but also kidney cancer in humans. Continued follow-up in the cohort study is warranted.