Progression from acral lentiginosis melanoma in situ to invasive acral lentiginosis melanoma

Acral lentiginous melanoma (ALM) is the most common type of cutaneous melanoma in Asians. The very early stage of ALM demonstrates only a proliferation of a few atypical melanocytes within the epidermis, and has been termed ALM in situ. A 74-year-old male patient presented with a pigmented lesion on the left great toe for 12 years, which had initially showed only a few scattered hyperplastic atypical melanocytes without dermal invasion upon biopsy 5 years ago. This time however, rebiopsy of the lesion confirmed a diagnosis of ALM, stage 1MB. It could be inferred that the lesion had slowly progressed from ALM in situ to invasive ALM over a period of 12 years. Herein we report a case of ALM in situ which progressed to invasive ALM over a long period of time. We expect this report may assist physicians in early recognition and proper management of future cases of ALM in situ. (Ann Dermatol 21(2) 185 ∼ 188, 2009).