Perianal lesions of BALB/c mice induced by 1,2-dimethylhydrazine dihydrochloride and methylazoxymethanol-acetate: their classification and histogenesis.

The histogenesis of perianal squamous cell carcinomas induced by subcutaneous and intraperitoneal injection of 1,2-dimethylhydrazine dihydrochloride (DMH) and painting of methylazoxymethanol (MAM)-acetate on the anal region was investigated in 212 female BALB/c mice. Painting of MAM-acetate and injection of DMH induced similar benign and malignant tumors and hyperplastic lesions in the anal region. In chronological studies on animals given DMH subcutaneously, cystic or solid squamous lesions, foci of immature sebocytes, sebaceous hyperplasias and sebaceous adenomas were identified. These lesions seemed to be precursors of carcinomas that developed in the same region, and originated from hair follicles or sebaceous glands of the pilosebaceous complexes, but not from the anal mucosa. In mice treated with DMH, the incidence of perianal carcinomas was high in groups with high incidences of colon carcinomas.