R that keratoacanthomas can be produced in the rabbit,l5 rat,1* hamster,lG mouse,16 hedgehog:' and chicken80 by the application of chemical carcinogens and that these tumors arise from the hair follicles.1* The keratoacanthoma is a common cutaneous tumor in man, but little is known about the etiological factors involved in its production, Familial, viral, and actinic factors have been incriminated as operative in certain cases: while the Occurrence of these tumors in pitch and tar workers and the results of work with experimental animals indicate that chemical carcinogens may play a part in the production of this lesion in man.16
We have studied 238 cases of keratoacanthomas treated at the Sheffield Royal Infirmary, Sheffield, England, over a period of 6 years. T h e purpose of this paper is to report the results of this study and tu present our assessment of the extent to which our observations correspond with the concept that chemical carcinogens may be involved in the production of this tumor in man. Also, whether the mechanisms involved are similar to those known to operate in experimental animals is discussed.
Methods
This histology files of the Pathology Department and case notes of the Skin Department were used in this survey. All available hist* logical material from skin tumors diagnosed as keratoacanthoma, papilloma, and squamous carcinoma over a period of 6 years (1 954-1 959) was re-examined. The case notes furnished the ages and addresses of the patients and the sites at which the tumor occurred. Question-