Multiple cutaneous papillomas and carcinomas that develop spontaneously in a mouse mutant, the repeated epilation heterozygote Er/+.

After a chance observation that multiple cutaneous papillomas and squamous cell carcinomas occurred in 2 adult mice heterozygous for the repeated epilation gene Er, we surveyed a panel of 10 +/+ (wild type) and 30 Er/+ (heterozygous) mice from birth to over 2 years of age. Homozygous Er/Er mice could not be included since their defect is lethal at birth. Whereas no cutaneous tumors developed in the +/+ mice, 20 of the Er/+ mice, males and females, had developed 1-5 cutaneous papillomas and at least 1 cutaneous invasive squamous cell carcinoma by 2 years of age. No lesions were seen in mice younger than 6 months old. Although almost all Er/+ mice died with their tumor burden, no metastases have yet been proven histologically. The Er/+ mouse should serve as a useful model for the exploration of genetic factors in cutaneous squamous cell carcinomas in humans.