Actinic keratoses (AK) are common cutaneous lesions associate with chronic ultraviolet radiation exposure. Ultraviolet radiation produces local and systemic immunosuppression, mutations in the p53 tumor suppressor gene, and deoxyribonucleic acid pyrimidine covalent dimmers, each of which is believed to contribute to the dysplasia seen in AK. While most authorities consider AK as a pre-malignant lesion, some consider it as an incipient squamous cell carcinoma (SCC). The risk for progression to SCC for an individual AK is reportedly low but highly variable; however, as patients often have multplie AKs, the overall risk for progression over a lifetime can be significant; thus treatment of AKs is warranted. In addition, the skin around clinically obvious AK lesions has been subject to the same chronic ultraviolet exposure, resulting in genetic damage and mutations, resulting in "field cancerization." Subclinical AKs may progress to clinical AKs, or even de novo invasive SCCs.

Among the current therapies for the treatment of AK are excisional surgery, cryosurgery, electrodessication and curettage, topical chemotherapy and light therapies. With provider-administered devices, temperature utilized, times of contact, and other variations in administration, influence efficacy of treatment. Efficacy can be improved by increasing the freeze time, but this is often associated with greater discomfort, more severe skin necrosis, and increased risk of post-treatment hypopigmentation. In addition, as with other lesion-directed therapies, cryosurgery does not treat subclinical lesions in the surrounding skin. Treated lesion clearance rates at 3 months post-treatment after double-freeze thaw cryotherapy has been reported to be around 76-88%; however, new lesions in the treatment field were not included. Overall lesion clearance rate, including new subclinical lesions, at approximately 5 months post-cryosurgery has been reported to be 35-51%. There is limited information on long-term AK clearance rates after cryosurgery and those reports differ in their methods of calculation. In a study comparing cyrotherapy, imiquimod and 5-fluorouracil, at 12 months post cryotherapy 28% (7/25) had complete clearance of baseline lesions that had undergone cryotherapy, but only 4% (1/25) had complete clearance of the treatment field.

Imiquimod is a topical immune response modifier that activates the innate immune system via Toll-like receptor 7, as well as enhances the acquired immune system. A 5% topical formulation has been approved for the treatment of AKs in the US as a 2x/week for 16 week regimen and in Europe as a 3x/week for 4 week regimen for 1 or 2 courses of therapy. Topical imiquimod treatment may also reduce subclinical lesions in the treatment area, resulting in fewer "new" AK lesions developing over the same period of time when compared to focal treatment. In a comparison of cryosurgery versus imiquimod for the treatment of AKs, Krawtchenko et al reported initial complete clearance rates of 68 and 85% by clinical assessment, respectively. However, the treatment field sustained clearance rate was 4% versus 73%, respectively. Tan et al reported that while application of imiquimod or vehicle following cryosurgery resulted in comparable target AK clearance rates at 12 weeks of 79% versus 76%, respectively, the imiquimod group had fewer total AKs and fewer subclinical AKs.

The imiquimod 5% formulation has limitations for the treatment of AKs. It is approved for the treatment of a small area of skin (25 cm2), uses a less than intuitive 2 times per week (2x/week) dosing schedule, and has a prolonged treatment period (16 weeks). Dosing more frequently than 3x/week with imiquimod 5% cream was not well tolerated in subjects with AK. Imiquimod cream at a concentration of 3.75% has been found in Phase 3 studies to be superior to placebo cream with respect to clearance of AKs using a regimen of up to 2 packets (250 mg of cream per packet, 500 mg total) applied daily to the entire face (approximately 200 cm2) for two 2-week treatment cycles separated by a 2-week no-treatment period.