• Participants must have a diagnosis of cutaneous squamous cell carcinoma that has been biopsied and confirmed histologically. Mixed histology (such as basosquamous carcinoma, sarcomatous carcinoma) is allowed.

• Participants must have a skin tumor that measures 10 - 39 mm (not less than 10 mm and not more than 39 mm) in longest dimension by clinical exam. (Participants may have more than one untreated CSCC at the time of enrollment, but only one CSCC may be treated with the study agent.)

• Participants must be candidates for treatment (excision) by Mohs micrographic surgery.

• Age ≥18 years. Because CSCC is exceptionally rare in patients \<18 years of age, children are excluded from this study.

• ECOG performance status ≤3 (Karnofsky ≥40%, see Appendix A).

• Ability to understand and the willingness to sign a written informed consent document.

• For participants with a past medical history of Human immunodeficiency virus (HIV), they must be on effective anti-retroviral therapy with undetectable viral load measured within the 6 months prior to enrollment.

• For participants with a past medical history of chronic hepatitis B virus (HBV) infection, the HBV viral load must be undetectable on suppressive therapy, if indicated.

• For participants with a past medical history of hepatitis C virus (HCV) infection, they must have been treated and cured. For participants with HCV infection who are currently on treatment, they are eligible if they have an undetectable HCV viral load.