Melanoma in the nail unit accounts for less than 1 percent of melanoma cases in white-skinned individuals, making it extremely rare, according to the DermNet NZ. While it is no more common in other races by incidence rate, it is the most common type of melanoma in darker-skinned patients.
Melanoma in the nail bed is separated into three groups: subungual melanoma, which originates from the nail matrix, or tissue under the nail root; ungual melanoma, which originates under the nail plate; and periungual melanoma, which originates from the skin beside the nail plate. Diagnosis of all of these forms most often occurs between the ages of 40 and 70, states DermNet NZ. It is not believed to be connected to sun exposure, and some experts suggest that it may be connected to trauma, which explains the higher rate of incidence in the big toe and thumb.
Doctors must remove cases of melanoma in the nail bed surgically, which can require the removal of the entire nail bed and sometimes the amputation of the end of the affected finger or toe, notes DermNet NZ. Once the melanoma is removed, patients have anywhere from a 16 percent to an 87 percent five-year survival rate. Because this type of skin cancer is difficult to identify, discovery of the melanoma usually occurs in the later stages, which increases the chances of the disease spreading to the body's lymph nodes.