Subungual Melanoma: Causes, Diagnosis, and Treatment

Subungual melanoma, sometimes called nail apparatus melanoma, is a type of malignancy that arises in the tissues of the nail bed. Melanoma cancers develop in cells called melanocytes. Melanocytes are cells that produce melanin, the pigment that gives skin, hair, and eyes their color.

Subungual melanomas can occur on any of the fingernails or toenails. These nail cancers are often misdiagnosed as a fungal infection due to their characteristic changes in color and nail texture.

Melanoma of the nail is a relatively uncommon condition, affecting 0.7% to 3.5% of people with malignant melanomas worldwide. It tends to occur more in darker-skinned individuals, including African-American, Asian, and Hispanic populations.

It's also more common as you age, with one study finding people were diagnosed at an average age of 69 years and 60% of them were male.

Symptoms

Subungual melanomas usually appear as darkened streaks that run longitudinally (perpendicular to the cuticle). Roughly half of these streaks are brown, blue, or black, while the other half are non-pigmented.

As cancer progresses, more streaks may appear, often with different colors. As time progresses, the portion closest to the cuticle may become wider.

This helps differentiate it from other nail-related conditions in terms of its uniformity, longitudinal discoloration, and involvement of the cuticle.

As the melanoma continues to grow, it can cause bleeding, the formation of a nodule, or deformity to the nail itself.

Causes

The reasons for why subungual melanomas develop remain unknown, but there are risk factors associated with its development. These include:

• Previous trauma to the fingers or toes (a common finding)
• Personal or family history of melanoma
• Multiple moles
• Genetics, such as those affecting people with the hereditary condition xeroderma pigmentosa (extreme sensitivity to UV radiation)
• Immune suppression, including people who are organ recipients or live with advanced HIV

Diagnosis

A diagnosis of subungual melanoma will usually be made with careful inspection of the nail and lesion. Dermatologists will use a tool called a dermascope, which provides a magnified view of the nail and surrounding tissue.

Ultimately, a visual examination has its limitations, especially since subungual melanoma is so infrequently seen. As a result, it's often mistaken for more common conditions, such as:

• Subungual hematoma, a bruising beneath the nail which lacks the uniformity of subungual melanoma
• Fungal infections (onychomycosis) which more often have dark, non-longitudinal stripes accompanied by yellow or white streaks
• Moles (nevi), which are less likely to appear in streaks
• Deposits of melanin beneath the nail which can occur as a result of pregnancy (as well as chemotherapy or radiation therapy)

A definitive diagnosis can only be made with a biopsy. Typically, an excisional biopsy is performed to remove the entire lesion plus some of the surrounding tissue. A less-invasive punch biopsy may be used if the signs are uncertain.

Staging of Melanoma

Depending on the size and depth of a subungual melanoma, further testing will be needed to determine the stage of the disease. As with other forms of cancer, the stage can vary from carcinoma in situ (pre-cancer) all the way to stage 4 metastatic disease (where cancer has spread to other organs).

To determine whether the melanoma has metastasized, there are various tests the oncologist can perform. They include:

• Biopsy of sentinel lymph nodes (the nodes nearest the tumor)
• Imaging techniques such as computerized tomography (CT scan)
• Positron emission tomography (PET scan)

Treatment

The treatment of subungual melanomas has changed considerably in recent years. In the past, amputation of the entire toe or finger was considered the treatment of choice.

Today, many subungual melanomas are treated more conservatively with only the local removal of the tumor. When amputation is indicated, it often involves only the first joint nearest the fingernail. For toenails, amputation to the second joint is more common.

For advanced subungual melanoma, other types of therapy may be needed, including:

• Chemotherapy, given either systemically through a vein or directly into the tumor
• Radiation therapy, used primarily as a palliative treatment to decrease pain
• Immunotherapy, a newer form of cancer therapy that aims to stimulate the immune system to fight cancerous cells
• Targeted therapies, such as drugs able to target the genetic KRAS mutations and BRAF mutations often found in nail melanomas

Response to treatment can vary based largely on the stage of cancer. Outcomes for people with subungual melanoma tend to be poorer than other types of melanoma, often due to delay in seeking diagnosis and treatment.

One study of 118 people with nail cancer who had sentinel lymph node biopsies found that:

• Melanoma of the nail was found at stage 1 in 33 people.
• The nail cancer was identified at stage 2 in 56 people.
• Subungual melanoma was diagnosed at stage 3 in 29 people.

The overall 5-year survival rate in this group was 69.5%, but the outlook is much lower for people diagnosed with stage 4 subungual melanoma, at just 15–20%.

A Word From Verywell

If you've been diagnosed with subungual melanoma, it's important to find a specialist experienced with the disease. Subungual melanomas are fairly uncommon, and the lack of experience can result in an unnecessarily aggressive approach to treatment.

While having an excellent care team around you is important, you remain the most important facet of that team. Learn as much as you can about your cancer. Ask for and accept help. Become involved with online support communities that can share their experiences and insights.