Tumors of the pilosebaceous unit induced in the rat by the intravenous administration of 7,12-dimethylbenz(A)anthracene.

Six of 70 female Sprague-Dawley rats given a single intravenous injection of 7,12-dimethylbenz[a]anthracene (DMBA) developed 7 pilosebaceous tumors. Two of the tumors showed differentiation toward the upper portion of the pilosebaceous unit while 5 showed differentiation toward the lower portion. Each tumor was examined histochemically for the presence of inner root sheath keratin of the hair follicle using the carbamido diacetyl reaction for citrulline and for hair shaft keratin using boiling ninhydrin reagent. The 2 tumors of the upper portion of the pilosebaceous unit were sebaceous adenomas which were accompained by a keratinizing epithelim like that of the sebaceous gland duct and upper pilosebaceous canal. Histochemically, the keratin was not like that of hair shaft nor inner root sheath. The 5 tumors showing differentiation toward components of the lower pilosebaceous unit were trichoepitheliomas. They were composed of structures which, to varying degrees, recapitulated the organization of the normal hair follicle. Within these follicular structures, both inner root sheath and hair shaft type keratins were found. The occurrence of skin tumors after the intravenous administration of DMBA was unexpected since it is uncommon for skin tumors to be produced by the systematic administration of chemical carcinogens and they have never been described after the oral administration of DMBA. That the route of administration may influence tumor production with this carcinogen is suggested by the fact that the only other reported tumors, which were squamous carcinomas, also followed intravenous injection of DMBA.