Following lentigo maligna may not prevent the development of life-threatening melanoma.

BACKGROUND Management of lentigo maligna (Hutchinson's melanotic freckle, in situ lentigo maligna melanoma) by regular observation relies on the detection of invasive melanoma before it has developed significant life-threatening potential. Recent studies indicate that lentigo maligna melanoma does not have a better prognosis than other forms of melanoma. OBSERVATIONS A case is reported of an amelanotic lentigo maligna that evolved from a macular lesion to a deeply invasive, amelanotic, lentigo maligna melanoma within 6 months. The melanoma was Clark level IV and measured 3.0 mm in maximum tumor thickness. CONCLUSIONS Observation of lentigo maligna at 6-month intervals would not seem to be sufficiently reliable in detecting the development of invasive lentigo maligna melanoma before it becomes a life-threatening disease. Early surgical excision is the treatment of choice.