Safety, Tolerability, and Efficacy Study of CLL442 in Patients With Cutaneous Squamous Cell Carcinoma in Situ (SCCis)

Inclusion Criteria: 1. Written informed consent has been obtained. 2. Male and female patients, age ≥ 18 to ≤ 90 years (at the time of the screening visit). 3. A primary, clinically diagnosed and histologically confirmed cutaneous SCC in situ lesion, with or without the involvement of the follicular unit, and histologically diagnosed within 30 days of the screening visit. The post-biopsy residual SCCis lesion must be visually evident and at least 3 mm in either length or width. 4. The lesion must be located in a place easily accessible for topical application by the patient or their caregiver, excluding the genitals, perianal area, sub-ungual area, eyelids, ear and must be \>1 cm away from the eyes and mouth. Exclusion Criteria: 1. Evidence of dermatological disease or histological evidence of a confounding skin condition in the treatment area, including but not limited to BCC, worse level/grade of SCC, rosacea, psoriasis, atopic dermatitis, eczema, xeroderma pigmentosa, verrucous lesions or any other tumor in the biopsy specimen. Lesions with atypical histology such as: spindle cell SCC, acantholytic SCC, clear cell SCC, adenosquamous SCC, desmoplastic SCC or lesions that have been present for a short time and have been fast growing. 2. Treatment of the target SCCis lesion within 8 weeks of screening visit by any of the following treatments: Liquid nitrogen, Photochemotherapy (PUVA), Long wave ultra violet radiation (UVB light), surgical excision or curettage within 1 cm of target lesion.; Systemic retinoids.; Ionizing radiation or interlesional injections or; Undergone a facial resurfacing procedure, i.e., chemical peel, laser resurfacing, dermabrasion, within the target lesion; 3. Treatment with the following topical agents within the 4 weeks prior to the screening visit: Levulanic acid, 5-fluorouracil, corticosteroids, retinoids, diclofenac, hyaluronic acid, imiquimod. 4. History of recurrence of the target SCCis lesion. 5. Systemic use of immunosuppressive drugs within 4 weeks prior to screening visit or during the treatment period - Photodynamic therapy or immunomodulators, cytotoxic drugs, or interferon/interferon inducers within 4 weeks prior to study entry or expected during the study. 6. Women of child-bearing potential, unless they are using at least basic methods of contraception during dosing of investigational drug. 7. Pregnant or nursing (lactating) women.