Formaldehyde and tumors in hamster respiratory tract

Male Syrian golden hamsters were exposed to 10 ppm of formaldehyde (H₂CO) 5 times/week for lifetime. Survival of the treated animals was reduced relative to unexposed controls. No tumors were observed in histologic sections of respiratory tract tissues from either unexposed or treated animals. Only a minimal increase in hyperplastic and metaplastic areas was observed in nasal epithelium of exposed animals. However, there was evidence that H₂CO could serve as a cofactor in the incidence of respiratory tumors induced by diethylnitrosamine (DEN). Animals were exposed once per week to 30 ppm H₂CO (5 h/day) for lifetime. No tumors were observed in the respiratory tract of the H₂CO-only control group exposed to this regimen. Hamsters receiving exposures to H₂CO at 2 days prior to each of 10 weekly DEN injections had a higher number of tracheal tumors/tumor-bearing animal at autopsy than those receiving DEN alone.