Abstract
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 IIIB. 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.