Melanoma is a cancerous growth of melanocytes that produce melanin. The type of melanoma that typically affects the toenail is acral lentiginous melanoma. In the United States, acral lentiginous melanoma (ALM) accounts for about 5% of all diagnosed melanomas. It also is the most common form of melanoma in Asians and people with dark skin, accounting for 50% of melanomas that occur in people with these skin types.
ALM is sometimes referred to as a “hidden melanoma” because these lesions occur on parts of the body not easily examined or not thought necessary to examine. ALM develops on the palms, soles, mucous membranes (such as those that line the mouth, nose, and female genitals), and underneath or near fingernails and toenails.
ALM is often overlooked until it is well advanced because in the early stages, it often looks like a bruise or nail streak. Here is what it usually looks like on each area of the body:
o Palm or sole – Melanoma usually begins as an irregularly shaped tan, brown, or black spot. It is often mistakenly attributed to some recent injury — that is, the patient recalls a relatively recent bruise or blow in the general area of the pigmented spot.
o Mucous membranes – When melanoma develops on a mucus membrane, it is most likely to develop inside the nose or mouth. Early symptoms include nosebleeds and nasal stuffiness and a pigmented mass inside the mouth. Melanomas also can develop on the mucous membranes of the anus, urinary tract, and female genitalia.
o Under a nail – The first sign may be a “nail streak” — a narrow, dark stripe under the nail. ALM usually develops on the thumb or big toe; however, it can occur under any fingernail or toenail. Many individuals, especially dark-skinned people, have fixed nail streaks that are completely benign. A new nail streak not associated with recent trauma, an enlarging nail streak, a wide or very darkly pigmented streak, or a nail that is separating or lifting up from the nail bed should be examined by a dermatologist. A possible indication of advanced ALM is a nail streak with associated pigmentation in the nail fold skin or destruction of the nail plate. ALM of the fingers or toes also can develop without an obvious nail streak — particularly the non-pigmented variety. ALM may, for example, look very much like a chronic infection of the nail bed.
Some types of melanoma can be treated with surgery alone while in other cases radiation or chemotherapy may be needed. With the advances in medical treatment, melanoma of the toenail is usually curable if it is caught in the early stages.