Effect of a Single Application of Croton Oil in Skin Carcinogenesis. ∗

Abstract

Conclusions

In our prior studies we had established that a single dose of 200 μg of the carcinogen DMBA is highly effective, giving rise to tumors of the skin in almost 50% of treated Swiss mice, of which a high proportion appear malignant, namely 28% become squamous cell carcinomas (2). A dose of 100 μg of DMBA, on the other hand, is a borderline carcinogen giving rise to a small proportion of papillomas many of which regress and few of which progress to malignancy. This result was confirmed. From other studies it is well known that a dose of 100 μg is an effective initiating dose of this carcinogen for the skin; that is, if it was followed by repeated applications of croton oil or some other promoting stimulus, many tumors would appear(10.11). In the present study this dose of carcinogen was combined with a single application of croton oil at 2 dosages. In no instance did croton oil, thus administered, give rise to any promoting effect, but to the contrary appeared. if anything, to engender a reduction in tumor incidence. This finding applied not only to combinations with the 100 μg dose of DMBA, but also to the 200 μg dose.

It thus seems clear that the difference in the carcinogenic capabilities of doses of 100 μg or 200 μg of DMBA cannot be explained on the basis of additional “injury” inflicted by the higher dose, if the “injury” is of the same type as that caused by croton oil. It is clear that the promoting effects of croton oil are quite distinct from the initiating and carcinogenic actions of DMBA since croton oil requires repeated applications to manifest its effect and has, if anything, the reverse effect under the conditions of the present expriment. The qualitative nature of the tumors seen in the croton oil treated groups appears consistent with that observed in many previous studies in that there was a predominance of benign and regressing lesions(2).