Abstract
The skin and lung tissues from SENCAR mice used as part of the Environmental Protection Agency's (EPA's) Carcinogenesis Testing Matrix were examined. This study included SENCAR mice used in three different short-term bioassay protocols in which the skin papilloma assay was used to identify initiators, promoters, and complete carcinogens. Also included were the pathology findings from SENCAR mice used in the combined bioassay in which the skin assay and the lung adenoma assay were conducted simultaneously. The gross and microscopic features of treatment-associated and spontaneous lesions of the skin and lung of the SENCAR mouse used in these studies are defined and the lesions most commonly observed are described. Generally, gross observations and microscopic findings in both the skin and lung tissues were poorly correlated. Although there are several definite criteria on which gross interpretations of the various skin and lung lesions can be made, with the exception of pedunculated squamous cell papillomas and the classic squamous cell carcinomas, the various lesion types had a wide variety of clinical presentations that severely compromised the accuracy of gross diagnosis. Further, in the case of benign skin neoplasms, malignant transformation of these tumors most often occurred at the base of the lesion and was initially hidden from gross observation. As a result, approximately 50% of the neoplasms interpreted clinically as benign tumors (papillomas and keratoacanthomas) were actually malignant neoplasms. Moreover, many lesions determined grossly to be nontumorous were in fact found to be neoplastic when examined microscopically. The SENCAR mouse was found to be more responsive in the lung adenoma assay than other strains examined with exception of the Strain A. Although accurate interpretation of the lung lesions in the SENCAR was compromised by nonneoplastic treatment-associated and/or spontaneous lesions, the feasibility of using the SENCAR skin and lung as target tissues in two-stage combined carcinogenesis studies merits further consideration.