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Lentigo maligna is a melanoma in situ that forms in sun exposed areas of skin, first described in 1892. Under the microscopic one sees a proliferation of atypical pigment cells in the superficial skin. They typically have a cloud like appearance with variable shades of brown coloring and start as a freckle that enlarges over a number of years. Historically they were called Hutchinson's freckle. More than half occur on the face or neck. They are more common in warmer climates with greater sunlight exposure and the majority occur after the 6th decade of life . If ignored long enough they will develop a vertical growth phase and begin to invade the deeper layers of skin, dermis. They are then malignant melanomas and are called lentigo maligna melanoma. At the time of presentation 10 to 20% of lentigo malignas have already invaded the dermis to some degree. Although melanoma represents a small portion of all skin cancers, it is responsible for the majority of skin cancer–related deaths.
The diagnosis of melanoma of the lentigo maligna subtype is challenging, as the clinical presentation is quite varied, ranging from a subtle brown patch to tan/black or even amelanotic(almost normal skin color). These lesions pose significant treatment challenges for clinicians because of significant invisible to the eye surrounding extension, a predilection for cosmetically and functionally sensitive areas, and a naming system that is often confusing. Obtaining a biopsy specimen from a clinically suspicious lesion can present problems, given the lesions can be as large as 6cm in anatomically and cosmetically sensitive areas. If the suspicious lesion is small, an excisional biopsy of the entire pigmented lesion to fat is recommended. However, an excisional biopsy is rarely feasible, as most lesions are too large with poorly defined margins to be completely removed. In this setting, a small biopsy of the darkest, or most palpable, or otherwise most visibly concerning area of the lesion is recommended.
