Observational Study of Topical Imiquimod Immunotherapy in the Treatment of Difficult Lentigo Maligna

Introduction Lentigo Maligna (LM) typically presents at sun-exposed sites in elderly patients as an asymmetric, slow-growing, irregularly pigmented macule with an irregular indented border. With changes in sun exposure behaviour LM is becoming more prevalent in middle-aged and younger adults.1 The risk of melanoma developing in LM increases with duration of the disease and therefore age,2 and is diffi cult to quantify, estimates range from 2.2%2 to 50%3 over a lifetime, once invasive disease is established, the tumour carries the same prognosis as other types of cutaneous malignant melanoma as defi ned by Breslow thickness and presence of ulceration. LM presents a diffi cult clinical problem and generally there is little consensus on the optimum form of management. The recommended guidelines for treatment of LM are surgical excision with excision margins into clinically normal skin of 2–5 mm.4,5 Others have suggested that up to 20% of cases of LM would require margins greater than this.6 However, lesions are commonly large and located on cosmetically important head and neck sites. Excision may result in a poor cosmetic outcome and it is diffi cult to justify this approach when the risk of malignant transformation may well be low. Amelanotic lentigo maligna also remains a signifi cant problem and inevitably results in incomplete excision since clinical identifi cation of disease extent is impossible.7 Non-surgical treatment options are used in 50% of U.K. patients over the age of 70, these include radiotherapy, retinoids,8 5-FU and azelaic acid. Cryotherapy, once popular, has fallen from favour because of reports of invasive melanoma occurring after cryotherapy ablation.9 Commonly a “watch and wait” policy is adopted. Imiquimod (Aldara, Meda Pharmaceuticals Ltd) is a topical immune response modifi er. The drug causes an increase in interferon locally and therefore may have a place in the management of superfi cial interferon sensitive malignancy. There are several reports of its use to treat lentigo maligna.10–12 We describe our experience with the use of imiquimod in a group of patients with LM on the head and neck where surgery was not an option.