This clinical trial proposes to evaluate a relatively unexplored approach to treatment of squamous cell carcinoma (SCC) on the lower extremities. The strategy is to directly and specifically deliver drug to the tumor. For the proposed phase I clinical trial, the investigators will perform intralesional injections of a well characterized, potent chemotherapeutic agent 5-fluorouracil (5FU) with and without a concomitant topical application of 5% imiquimod to kill topically accessible SCC cells. The goal of the study is to evaluate the safety profile and tolerability of intralesional-5FU with and without a concomitant topical imiquimod and measure the clinical objective response rate (ORR) in treated lesions compared to untreated lesions 3 weeks after treatment.