Atypical melanosis of the foot

We present a case of a seemingly malignant pigmented lesion on the foot, arising in a Japanese female. Clinically, the lesion was characterized by irregular borders and variegated pigmentation closely mimicking those of acral lentiginous melanoma in situ. However, the histologic findings revealed only focal, slight, melanocytic hyperplasia with minimal cytologic atypia along the basal layer. Despite the malignant clinical features, thorough histologic examination failed to disclose any area with significant melanocytic atypia or evidence of malignancy. To the best of our knowledge, no similar lesions with the clinical appearance of melanoma in situ and completely lacking histologic evidence of malignancy have been reported. We, therefore, prefer to designate this lesion as atypical melanosis of the foot, to highlight the clinically atypical findings and to distinguish this from malignant melanoma in situ of the foot (1).