Acral lentiginous melanoma (including in situ melanoma) arising in association with naevocellular naevi.

Acral lentiginous melanoma (ALM) occurring on the sole of the foot is the most common type of malignant melanoma in Asians, African and North American Blacks, but is relatively infrequent in Caucasians. According to the literature ALM is thought less likely to arise in a precursor naevus of any type or be associated with dysplastic naevi elsewhere on the skin. We present five cases of ALM (two invasive and three in situ cases) arising in association with pre-existing naevi on the foot in Asians and Caucasians. All patients were female, aged 35-66 years (mean = 47.8). Clinically, all five tumours demonstrated various shades of tan, brown and black, admixed with hypopigmented areas. Histologically, these melanomas showed a lentiginous character of the radial growth phase component with rare foci of pagetoid intra-epidermal spread. Invasive determal components in the form of epithelial and spindle cells were evident in two cases, with a measured depth of 1.7 and 0.85 mm, respectively. Pre-existing naevi, either dermal or junctional, were identified in all tumours. Clinical follow-up in all patients showed no evidence of recurrence or metastasis over a period of 4 months-5 years. These cases appear at variance with the general belief that ALM and ALM in situ arise de novo and rarely arise in precursor naevi. To the best of our knowledge, this is the first documented series of ALM in situ arising in association with pre-existing naevi. We conclude that ALM can arise in association with acral naevi.