Dose-Ranging Safety and Efficacy Study of Topical Creams Containing API 31510 for the Treatment of in Situ Cutaneous Squamous Cell Carcinoma

Inclusion Criteria: * Male or female adults ≥ 18 years of age * Primary, histologically confirmed SCCIS with a minimum area of 0.5 cm2 and with a maximum diameter of 2.0 cm target SCCIS lesion suitable for excision * Histological diagnosis made no more than 4 weeks prior to the screening visit * Histological biopsy removed 25% or less of the target lesion * No other dermatological disease in the SCCIS target site or surrounding area * Willing to refrain from using non-approved lotions or creams on the target site and surrounding area during the treatment period. Willing to refrain from washing the treated area for at least 8 hours following the application of study medication * Willing to refrain from exposure to direct sunlight or ultraviolet light and to avoid the use of tanning parlors for the duration of the study * Laboratory values for the tests listed in the Study Schedule on page 2 within the reference ranges as defined by the central laboratory, or "out of range" test results that are clinically acceptable to the investigator. * Ability to follow study instructions and likely to complete all study requirements * Written informed consent obtained, including consent for tissue to be examined and stored by the central dermatopathologist * Written consent to allow photographs of the target SCCIS lesion to be used as part of the study data * For females of childbearing potential, a negative pregnancy test at screening and using an acceptable form of birth control (oral/implant/injectable/transdermal contraceptives, intrauterine device, condom, diaphragm, abstinence, or a monogamous relationship with a partner who has had a vasectomy) Exclusion Criteria: * Pregnant or lactating * Presence of known or suspected systemic cancer * Histological evidence of nBCC, sBCC, or any other tumor in the biopsy specimen * Histological evidence of severe squamous metaplasia, infiltrative, desomoplastic or micronodular growth patterns in the biopsy specimen * History of recurrence of the target SCCIS lesion * Evidence of dermatological disease or confounding skin condition in the treatment area, e.g., BCC, actinic keratosis, rosacea, psoriasis, atopic dermatitis, eczema, xeroderma pigmentosa * Concurrent disease or treatment that suppresses the immune system * Chronic medical condition that in the judgment of the investigator(s) would interfere with the performance of the study or would place the patient at undue risk * Known sensitivity to any of the ingredients in the study medication * Use of a tanning parlor or other excessive or prolonged exposure to ultraviolet light or direct sunlight during the course of the study * Treatment with systemic chemotherapeutic agents within the 6 months prior to the screening visit * Use of systemic retinoids within the 6 months prior to the screening period * Treatment with systemic immunomodulators or immunosuppressants within the 6 months prior to the screening period * Use of topical immunomodulators within 2 cm of the target SCCIS lesion within the 4 weeks prior to the screening period * 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 * Undergone a facial resurfacing procedure, i.e., chemical peel, laser resurfacing, dermabrasion, within the 6 months prior to the screening visit, if the target SCCIS lesion is on the face * Treatment with liquid nitrogen, surgical excision or curettage within 2 cm of the target SCCIS lesion during the 4 weeks prior to the screening visit * Elective surgery within 4 weeks prior to the screening visit, during the study, or 4 weeks after the treatment period * Evidence of current chronic alcohol or drug abuse * Current enrollment in an investigational drug or device study or participation in such a study within 4 weeks of the screening visit * In the investigator's opinion, evidence of unwillingness, or inability to follow the restrictions of the protocol and complete the study