Squamous cell carcinoma (SCC) of the lower extremity is a distinct subset of cutaneous
      squamous cell carcinomas which tend to occur multiply in elderly women. In contrast, the
      majority of cutaneous SCCs occur on the head and neck, and in men more than women.
      Histopathological studies of lower extremity SCCs revealed that they tend to be well
      differentiated and have low incidence of perineural and lymphovascular invasion. SCCs of the
      lower extremity are also less prone to metastasis. Surgical excision has been the mainstay in
      the treatment of SCC, including lower extremity SCC. However, the lower extremity, as a site,
      is prone poor wound healing and postoperative complications such as infections. Furthermore,
      a phenomenon called eruptive postoperative SCC can occur, in which cytokines released during
      wound healing trigger secondary tumor formation in genetically predisposed cells surrounding
      the original SCC. Given that lower extremity SCCs are less aggressive but more prone to
      surgical complications when excised, the investigators believe these types of lesions may be
      good candidates for non-surgical treatment.

      5-fluorouracil (5FU) is a chemotherapeutic agent that has been used systemically for various
      malignancies, but it has also been used topically or intralesionally for a variety of
      dermatological conditions. But reports of its use in invasive cutaneous SCC, other than in
      keratoacanthomas, are very limited. The investigators are aware of 3 such reports in the
      literature. In the largest study to date, 6 weekly intralesional injections of
      5FU-epinephrine gel were performed on 23 patients with cutaneous SCC on various body sites,
      22 (96%) of whom demonstrated histologically confirmed tumor clearance. This study, however,
      used a proprietary gel formulation which is not widely available. There are two other case
      reports of successful treatment of SCC with 6-8 intralesional injections of 5FU at weekly
      intervals. The three published studies injected 0.6ml to 2.4ml of 5FU, per each weekly
      session, at concentrations of 30mg/ml to 50mg/ml.

      Imiquimod is a topical immune response modulator which acts through the toll-like-receptor 7
      pathway. It is FDA approved for the treatment actinic keratosis, genital warts, and
      superficial basal cell carcinomas. It has also been used off-label for the treatment of
      squamous cell carcinomas in situ and invasive cutaneous squamous cell carcinomas. A review of
      published studies to date found 50-88% clearance rate for squamous cell carcinomas in situ
      treated with daily application of topical imiquimod. There is only one study, other than case
      reports of treating invasive squamous cell carcinomas with topical imiquimod. In that study,
      7 out of 12 (71%) invasive squamous cell carcinomas cleared with topical imiquimod 5 days per
      week for 12 weeks. Common reported adverse reactions are erythema, pruritus, weeping,
      erosions, crusting at the application site.

      The aim of the proposed study is to evaluate a relatively unexplored approach to treatment of
      SCC on the lower extremities. The strategy is to directly and specifically deliver a drug to
      the tumor through an injection weekly for three weeks. For the proposed phase I clinical
      trial, the investigators will perform intralesional injections of a well-characterized,
      potent chemotherapeutic agent (5-fluorouracil) to kill topically accessible SCC cells.
      Importantly, 5-fluorouracil is currently in clinical use with a well-established safety
      profile. It is anticipated that intralesional injections of 5-fluorouracil (5FU) will enable
      direct and specific delivery of chemotherapy to the tumor, thereby reducing the potential for
      systemic toxicity. Further, intralesional injections of 5FU enable tumoral delivery of
      locally effective concentrations of 5FU using doses that are orders of magnitude below those
      used currently for the intravenous (IV) treatment of multiple malignancies.

      In addition to the 5FU injections, a subset of study participants will also have their
      lesions treated with a topical application of 5% imiquimod, another well-characterized
      chemotherapeutic agent with some demonstrated efficacy in treating cutaneous squamous cell
      carcinomas. The investigators hope that the concomitant use of topical 5% imiquimod will work
      synergistically with intralesional 5FU. No study published to date has been found on the
      concomitant use of intralesional 5FU and topical imiquimod.

      Participants will have at least 1 SCC lesion greater 1cm and less than 2 cm in largest
      diameter, on their lower extremities. The clinical diagnosis of SCC will be confirmed
      histologically by a deep shave biopsy of less than half of the lesion. The remainder of the
      lesion will be used for intralesional injections of 5FU or intralesional 5FU/topical
      imiquimod according to the following schema:

      In this study, a total of 30 participants will be randomly assigned into 3 groups.
      Randomization will be conducted using the University of Pittsburgh Cancer Institute (UPCI)
      randomizer, which is maintained by the Biostatistics Facility of UPCI
      (https://randomize.upci.pitt.edu/randomizer/home.seam).10 participants will serve as a
      control group, and will receive neither 5FU injection nor topical imiquimod. In another 10
      participants, intralesional injections of 50mg of 5FU in 1ml aqueous injectable solution will
      be administered weekly for 3 weeks. In yet another 10 participants, intralesional 5FU will be
      administered as in the previous group, additionally participants will also receive
      three-times-weekly topical application of 5% imiquimod to the same lesion. At the end of week
      two, a 2mm punch biopsy of the lesion will be obtained for mid-point analysis, and will be
      stored for tissue banking and future study. A week after the last injection (week 4), the
      lesion will be surgical resected in all participants including the control group, to render
      the patients disease free. Resection is the current standard of care for these tumors. A part
      of, or all of, the resected tumor and surrounding skin will be stored for tissue banking and
      future studies to characterize and compare the tumor microenvironment before, during, and
      after therapy.

      All lesions will be photographed and treatment response will be evaluated 4 weeks after the
      first 5FU injection prior to excision.