Many proprotein convertases (PC), especially furin and PACE4, are involved in pathological processes such as viral infection, inflammation, hypercholesterolemia, and cancer, and have been postulated as therapeutic targets for some of these diseases. In this chapter, we review mostly our work using animal models of squamous cancers that have been induced by chemical or UV carcinogenesis protocols to highlight the role of PCs in the development and progression of experimental tumors. After demonstrating in wild-type mice the role of PACE4 in tumor progression, as well as detecting the...