Controversies and evolving concepts in the diagnosis, classification and management of lentigo maligna

The diagnosis of lentigo maligna (LM) is often challenging for both clinicians and pathologists. LM is widely regarded as a form of melanoma in situ occurring in severely sun-damaged skin with characteristic clinical and pathologic features. However, compared with other forms of in situ melanoma, it often has a long-term clinical course for evolution to invasive melanoma. Some authorities advocate dividing LM into premalignant/precursor and in situ melanoma (LM in situ melanoma) phases, implying a lesser risk of the former for developing invasive melanoma. However, this subtle morphologic distinction does not necessarily correlate well with clinical outcome. An initial tissue sample for histologic diagnosis is commonly a small proportion of the lesion and may not be representative/diagnostic of LM. New clinical diagnostic tools including dermoscopy and in vivo confocal microscopy have improved the accuracy of both clinical diagnosis of LM and also defining the peripheral extent of the lesion for definitive treatment. In this review, the authors discuss these challenges and controversies in LM and provide recommendations for clinicopathologic diagnosis and management.