Black toenail melanoma, also called acral-lentiginous melanoma, is a rare form of skin cancer found under a toenail or a fingernail, according to Mayo Clinic. It can also form on the palms of the hands and soles of the feet. It usually affects people with darker skin, including African-Americans.
Melanomas found in people with darker skin are sometimes called hidden melanomas because they lurk in places people don't think to check, Mayo Clinic states. Other hidden melanomas include ocular melanoma, which affects the eye, as well as melanomas in the digestive tract, nose, mouth and vagina.
The first sign that someone may have acral-lentiginous melanoma is a narrow, dark streak under the nail that wasn't caused by a trauma, according to the AIM at Melanoma Foundation. Although many people have benign nail streaks, patients should see a doctor if the streak becomes wider or darker. Most often this type of cancer occurs in the big toe or thumb, but it can form under any fingernail or toenail.
Another symptom of black toenail or fingernail melanoma is a nail lifting up out of the nail bed, the AIM at Melanoma Foundation reports. Sometimes the cancer shows up without a dark streak and appears to look very much like a chronic nail fungus. In some patients, the nail plate is destroyed.