Subungual melanoma is a rare form of skin cancer that occurs under the nail, usually on the thumb or big toe. It appears as a longitudinal dark band that’s at least a few millimeters wide.
Unlike the more common melanomas that appear on the skin in more easily seen areas, such as the torso or the leg, subungual melanomas are often overlooked because they mimic so many other nail conditions. For instance, any trauma to the nail can cause a blood blister, which looks similar to subungual melanoma. Fungal or bacterial infections also can cause the nail to discolor.
Experts advise people over age 50 who notice symptoms such as a new dark spot under their nail or the widening of an existing dark streak to consult a dermatologist. Darkening of the associated cuticle or nail fold is particularly worrisome since it can reflect “Hutchinson’s sign,” which can indicate melanoma.
Surgery is usually warranted to remove the cancer completely. Because these growths are typically found when they’re advanced, the prognosis is poor, with a five-year survival rate of 59 percent, according to some estimates.