4. Treatment of Non-Melanoma Skin Cancer: Immunotherapy as a Viable Option

Abstract

Non-melanoma skin cancer (NMSC) is generally considered to be a worldwide epidemic. Current estimates predict that between 0.9 and 1.2 million new cases will be diagnosed each year in the United States of America (USA), which is one-third of all cancers diagnosed (1). In Australia, the incidence of NMSC continues to rise and it now affects at least 1% to 2% of the population annually (1, 2). NMSC tends to affect Caucasians particularly in areas exposed to sunlight, such as the head, neck and back of the hands. There is an increased risk with fair skin, blue eyes and a history of repeated sunburns (1). There are two main forms of NMSC, basal cell carcinoma (BCC) and squamous cell carcinoma (SCC), which account for 80% and 16% respectively (1). The majority of BCCs present as two varieties. Nodular BCC (nBCC) appears mostly on the head and neck and accounts for approximately 60% of all BCCs (3). Most of the remainder are superficial BCC (sBCC), which occur on the trunk and extremities (4, 5). Standard treatments for BCCs include excision, curettage and electrodesiccation, and cryosurgery (6). Other forms of treatment such as Mohs micrographic surgery, intralesional interferon (7) and radiotherapy, may be used depending on the nature, site and size of the tumor (6). Actinic keratosis (AK) is considered by some to be the earliest clinically recognizable manifestation of SCC in situ (8, 9). The risk of progression of AK to invasive SCC has been reported as ranging from 0.25 to 20% within 10 – 25 years (8, 10, 11). Sun avoidance measures and sunscreen protection are the first steps in the therapy of AK. The conventional approaches for treating AKs include cryotherapy, electrodesiccation and curettage, excision, CO2 laser therapy, 5-fluorouracil (5-FU), chemical peels and photodynamic therapy (12). Recently, topical immunotherapy in the form of imiquimod 5% cream has demonstrated efficacy for the treatment of BCC and AK. Imiquimod, an immune response modifier, has demonstrated in pre-clinical studies to have both antiviral and antitumor activity in vivo (13). It is currently recommended for the treatment of external genital warts induced by human papillomavirus (14 – 16). This paper reviews the evidence of the safety and efficacy of imiquimod for the treatment of BCC and AK. IMIQUIMOD FOR THE TREATMENT OF BASAL CELL CARCINOMA