Discrepancy between epidemiological evidence and animal experimental result

The tumorigenicity of arsenic trioxide was investigated in female Syrian Golden hamsters given 5.25 or 3.75 mg as arsenic in a total 15 intratracheal instillations once a week for 4 months. During observation of the entire life span, 5 pulmonary adenomas were manifested in 30 hamsters in the treated groups, while no pulmonary tumor was detected among 35 hamsters in the control groups. We concluded from this study that arsenic trioxide is tumorigenic to the lung of Syrian Golden hamsters but its tumorigenic potency is relatively weaker than other well known carcinogens.