Melanoma can develop and form under toenail and fingernail beds, explains Medical News Today. The resulting growth is dark blue or black in appearance and is often overlooked, especially in toes. Occasionally, the tumor lacks pigment, called amelanotic melanoma, making it difficult to identify under the toenail.
Typically subungual melanoma occurs underneath toenails, starting out as longitudinal lines of dark color that run down the length of the nail, states American Family Physician. This type of melanoma can also manifest as a dark spot on the nail bed. This pigment occurs when the tumor has reached the matrix or material of the nail.
Acral-lentiginous melanoma is a hidden melanoma difficult to identify because it largely occurs in darker-pigmented individuals, reports Mayo Clinic. Melanoma is one of the most deadly kinds of skin cancer, and it occurs when pigment cells grow abnormally.