Acral lentiginous melanoma (ALM) involves the palms, soles, and nail beds. It is the most common type of melanoma in patients of African or Asian descent. Delays in diagnosis result in more advanced disease at the time of diagnosis. Trauma or chronic inflammation have been considered as etiologic factors. As opposed to melanomas in sun-exposed sites, which typically are associated with BRAF or NRAS mutations, ALM often display activating mutations of wild-type KIT (1).
Lending further credence to the hypothesis that trauma may be etiologic in ELM, Minagawa et al performed a compelling study of 123 patients (54 men and 69 women) with plantar melanoma (PM). They mapped the distribution of PM on a digital grid and found that 50 lesions were on the rear (heels) 32 on the front (MTP region), 14 on the midfoot, but only 3 on the arch (that adds up to 99 patients; I assume that the other 24 were scattered on other sites of the foot but there is no mention of that in the article). Lesions were equally divided between the right foot (62) and left foot (61). Breslow thickness ranged from in situ to > 4 mm. The mean age of patients was 73.5 years. The authors note that the distribution of PM correlates with the locals of the highest mechanical and sheer stress (2).
I cannot help but wonder about the location melanomas of the palm. Do those correlate with callouses in construction workers or golfers? Would diminution of mechanical stress (orthotic shoes, wearing golf gloves, etc.) decrease the risk of ALM?
When screening for melanoma, one thing is certain – you should put your foot down and insist that your patients take their socks off so you can examine their feet.
- Goydos JS, Shoen SL. Acral lentiginous melanoma. Cancer Treat Res 2016; 167: 321-9.
- Minagawa A, et al. Melanomas and mechanical stress points on the plantar surface of the foot. N Engl J Med 2016; 374; 2404-6.