Non-melanoma skin cancers, including basal cell carcinoma (BCC) and squamous cell carcinoma (SCC), are increasing in prevalence globally. An estimated 1 million cases occur in the United States annually. BCC is the most common skin cancer in South Africa, with SCC a close second. Actinic keratosis (AK), meanwhile, will occur in 1 in 6 light-skinned individuals during their lifetimes. Topical therapies are preferred in the treatment of AK and skin cancers, since this is a non-invasive approach that reduces the risk of pain, infection and scarring. The primary non-ablative treatment options are 5-fluorouracil (5-FU), imiquimod 5% cream and diclofenac 3% gel.
Imiquimod activates the body’s innate immune response, including dendritic cells and cytokines. Because toll-like receptors have a central role in the immune response, toll-like agonists like imiquimod can activate the body’s innate and adaptive immunity simultaneously. Imiquimod serves to upregulate Th1 response and downregulate Th2 response.
Imiquimod locally induces cytokines and chemokines via toll-like receptor 7 on dendritic cells, macrophages and monocytes in vitro. There is less chance of recurrence after use of imiquimod because of cellular memory. The current data also suggests that imiquimod may induce tumour apoptosis. The 2002 pilot study of the treatment of AKs with imiquimod, launched by Prof Stockfleth, found that imiquimod completely cleared 84% of cases within 14 weeks.