DS03 Lentigo maligna: is it time to put down the scalpel?

Abstract Lentigo maligna (LM) is a subtype of melanoma in situ that often proves to be a diagnostic and therapeutic challenge. Treatment aims to prevent progression to an invasive tumour called lentigo maligna melanoma (LMM). In the UK, common treatment modalities include conventional excision, staged re-excisions, slow Mohs surgery or expectant monitoring. Although considered the ‘gold standard’, surgical excision of LM can be disfiguring as it frequently affects cosmetically sensitive areas requiring complex surgical reconstructions. Topical imiquimod 5% presents a pragmatic alternative treatment modality without the need for surgery. In vivo reflectance confocal microscopy (RCM) allows real-time noninvasive delineation of LM. Evidence suggests this is an effective diagnostic tool for pre- and post-treatment evaluation (Brand FL, Jafari SM, Hunger RE. Confocal microscopy and lentigo maligna: an in vivo pilot study for the assessment of response to imiquimod therapy. Dermatology 2019; 235:150–5). We retrospectively analysed 35 cases of histologically confirmed LM that completed treatment with imiquimod between 2018 and 2022. The average patient age at diagnosis was 73.9 years, with a female : male ratio of 18 : 17. Following assessment with RCM, patients were prescribed a protocol of topical imiquimod 5% once a day, 5 days per week for 12 weeks, along with instructions to apply this 10 mm beyond the mapped area or a cosmetic unit (Australia and New Zealand Melanoma Trials Group RADICAL trial). Patients were counselled about expected side-effects; all completed the course and achieved significant inflammation and superficial ulceration. To ensure a response was achieved, the following stepwise interventions were used: application increased to 7 days per week, occlusion with a dressing and addition of a topical retinoid. Repeat RCM was performed 6 months after treatment completion. At this point, 30 of 35 (86%) patients responded with no evidence of residual LM on RCM. Three cases required a second course of treatment. Two of these were shown to be clear on RCM, while the third is clinically clear and awaiting RCM confirmation. A fourth patient was lost to follow-up. A further patient has failed two courses and is about to embark on a third round of treatment. In total, 16 cases completed the 12-month review and maintained clearance. We demonstrate that imiquimod is an effective treatment for LM, potentially avoiding extensive surgery and complex reconstruction. Reflectance confocal microscopy can be used to delineate the extent of the LM and assess the post-treatment response. Our preliminary data suggest a significant proportion of LM cases achieved clearance with no recurrences to date. Follow-up of these patients will help evaluate the long-term efficacy of imiquimod, but our data suggest this treatment protocol provides a promising alternative to surgical intervention.