Formaldehyde and skin carcinogenesis

Groups of 32 animals (16 males/16 females) were given topical application of 200 μg 1% formaldehyde or 10% formaldehyde in water on the backskin twice a week. Two other groups were painted with 51.2 μg DMBA in 100 μL reagent grade acetone: one was followed 9 days later with applications of 200 μl 10% formaldehyde in water twice a week, and the other with 17 nmol TPA in 100 μL acetone twice a week. A fifth group of 176 mice was treated once with 51.2 μg DMBA in acetone and given no further treatment. The animals were painted and/or observed for 60 weeks. The animals painted once with DMBA alone were observed for 80 weeks. Animals receiving 1 and 10% formaldehyde alone developed no tumors. The 176 mice painted once with DMBA developed 225 skin tumors in 85 animals. Six of them were squamous cell carcinomas and 2 animals had lymphosarcomas. In the group painted with DMBA and then followed by formaldehyde, three animals had lung adenomas, and 11 had neoplastic growths of te skin (three squamous cell carcinomas and 22 papillomas). The final tumor rate after DMBA initiation followed by formaldehyde was not significantly different from the final tumor rate after DMBA alone, but the time of appearance of the first tumor and the mean latency time was significantly or very significantly, reduced. Hence, under the experimental conditions used formaldehyde had no carcinogenic potency of its own but did shorten the latency time in DMBA-induced carcinogenesis.Formaldehyde has also acute toxic and irritating effects. It is therefore important to induce practical methods for reducing exposure to formaldehyde in pathology laboratories.