What Is Subungual Melanoma?

What do You Need to Know About Subungual Melanoma?

Wrinkled hands as it's important to examine your hands for a subungual melanoma
What is a subungual melanoma, what symptoms should you be aware of, and how are they treated?. Nurcholis Anhari Lubis / Stringer / Getty Images

If you've been told you have a subungual melanoma you're probably very frightened. Is this a type of malignant melanoma? What are the causes, and how is it treated? Since these cancers are frequently misdiagnosed, what else could it be?

What is Subungual Melanoma? - Definition

Subungual melanoma, also referred to as melanoma of the nail unit, is a cancer which arises in the tissues of the nail bed (also called the nail matrix.) Melanomas are cancers which begin in melanocytes, the melanin secreting cells in our skin which are responsible for producing a suntan.

These cells are located in the basil layer of the epidermis, the top of the three layers of the skin.

Subungual melanomas are most commonly found on the thumb or great toe, but may occur on any of the fingers or toes. They are often misdiagnosed, either being attributed to something else, or having another condition, such as a fungal infection, at first thought to be a melanoma.

Subungual melanoma is relatively uncommon, being responsible for only one to two percent of all melanomas in Caucasions. Though it is not more common in darker skinned people, subungual melanomas represent a higher percentage of melanomas in those with darker skin colors. In Asians, it's thought that 20 percent of melanomas are subungual melanomas. They occur most often in people between the ages of 40 and 70.

Symptoms and Appearance of Subungual Melanoma

Subungual melanomas usually appear as a longitudinal line (a line parallel to the finger or toe) and can be nearly any color.

Roughly half of these are brown, blue, or black, with the other half being flesh colored (unpigmented.) As the cancer progresses, more streaks may appear and these may be of different colors. As time goes on, the portion of the streak closest to the base (by the cuticle where the nail originates) may become wider than the distal part of the finger or toe (area farthest away from the body.) The line or streak is usually wider than 0.3 millimeters in width.

(Melanomas that arise in the skin on one side of the nail are instead referred to as periungual melanomas.)

Hutchinson's sign is a common finding in most, but not all subungual melanomas. This refers to the appearance in which the "streak" extends all the way to the nail bed or nail fold (where the nail begins to grow) and into the cuticle. In contrast, bleeding under the toenail which is common (subungual hematoma) often is lighter near the nail bed as new tissue appears.

As the melanoma grows it may eventually result in deformity of the nail, a nodule, or bleeding.

The classic ABCD's of melanoma are less helpful in diagnosing nail unit melanomas than other types of melanomas, but are still important for everyone to know. These letters stand for:

  • A - Asymmetry
  • B - Irregular border
  • C - Color, classically referred to as "red, white, and blue"
  • D - Diameter greater than a pencil eraser
  • E - Elevated (which doesn't apply to subungual melanomas until they are quite advanced)
  • F - "Funny looking" 

Diagnosis

A diagnosis of subungual melanoma begins with careful inspection of the lesion.

Dermatologists often use a technique called dermascopy, which is essentially a careful exam using an instrument like a magnifying glass.

A diagnosis, however, can only be made for certain with a biopsy. There are different biopsy techniques which may be used, but usually an excisional biopsy is the preferred method. In an excisional biopsy the entire lesion plus some surrounding tissue is removed. In some cases a punch biopsy or incisional biopsy may be used, especially if the lesion is not likely to be a melanoma.

Differential Diagnosis - What Else Could it Be?

As noted earlier, misdiagnosis is common with subungual melanomas, with the possibility of both missing a diagnosis and believing it is something else, or incorrectly making a diagnosis of melanoma when the lesion is something else. There are several processes that may cause what is referred to as longitudinal melanychia, or the deposit of melanin in lengthwise lines under the nail bed. Some other processes which can look like a subungual melanoma include:

  • Subungual hematoma - This is essentially a bruise under the nail bed. Unlike melanomas, these do not occur in a line and may appear as several different shapes depending on the cause. They usually become less noticable over a period of time, and normal nail tissue (minus the line) can be seen growing in at the base. With a subungual hematoma, in contrast, the symptoms come on rapidly over a day or two following trauma or vigorous activity using the hands or feet.
  • Fungal nail l infections (onychomycosis) - In contrast to subungual melanomas, fungal infections are more likely to cause dark stripes which are non-longitudinal, and may be accompanied by yellow or white streaks of the nail as well as scales on the surface.
  • Mole (nevus) of the nail matrix - A "mole" may appear in this location, though again, is less likely to occur in a line.
  • The deposit of melanin under the nail may also occur in pregnancy, and under conditions which activate melanocytes such as chemotherapy and radiation therapy.

In some cases it is difficult to distinguish a subungual melanoma from these other processes, or even normal melanin deposition under the nails in darker skinned individuals. It is important, for that reason, to have a biopsy performed if there is any question, and to have the results read by a pathologist who is experienced in diagnosing subungual melanomas.

Staging

Depending on the size and depth of a subungual melanoma, further testing may be done to determine the stage of the disease. As with many other cancers, the stage can vary from carcinoma in situ all the way to stage 4 or metastatic disease.

At the time of surgery, your surgeon may suggest a sentinel node biopsy. When cancers spread, they often first spread to nearby lymph nodes. A sentinel node biopsy is a procedure in which a dye (and a radioactive tracer) are injected in order to identify the first lymph node to which a cancer would likely spread, and then performing a diagnosis of that lymph node. Instead, a lymph node dissection may be performed, in which nearby lymph nodes are removed and evaluated for the presence of tumor.

Imaging tests such as CT scans and PET scans may also be done to look for the spread (metastasis) of the cancer to distant organs. The areas to which a subungual melanoma is most likely to spread include the lung, liver, bones, brain, and digestive tract organs. Learn more about how cancer spreads.

Causes and Risk Factors of Subungual Melanoma

While we don't know exactly what causes subungual melanomas, we do know of some risk factors for their occurrence. Unlike melanomas in other regions of the body, however, subungual melanomas do not appear to be caused by sun exposure. Risk factors which have been correlated with these cancers include:

  • Previous trauma to the fingers or toes (this is a common finding)
  • Personal or family history of melanoma
  • Multiple moles (nevi)
  • Genetics - People with some hereditary conditions such as xeroderma pigmentosa are more likely to develop a subungual melanoma
  • Suppression of the immune system, for example, from HIV, chemotherapy, or blood related cancers such as lymphoma

Treatment of Subungual Melanoma

Surgery - The treatment of subungual melanomas has changed in recent years. In the past, amputation of the digit (toe or finger) in which the cancer was found was usually the treatment of choice.

At this time, wide local excision of the tumor is instead the usual approach, though amputation may still be required. A 2014 review of all the literature to date on cases of subungual melanoma suggests that this more conservative approach may work just as well, and that amputation didn't seem to improve survival.

Amputation of part of the finger or toe is still often needed, with amputation at the distant joint in a finger (the one farthest from the body) for fingers, and at the second joint in toes common.

It's very important to find a surgeon who has experience in these surgeries. The goal of surgery is to remove the tumor but retain as much length and joint mobility with as much preservation of  function and sensation as possible.

Treatments for advanced subungual melanomas - For subungual melanomas which have spread (either to lymph nodes or to distant regions) further therapy beyond surgery will be needed. Options may include:

  • Chemotherapy - Most chemotherapy is given as a systemic therapy, through a vein and designed to reach cancer cells anywhere in the body. In some cases, chemotherapy isolated to a digit may be an option.
  • Targeted therapies - Around 50 percent of people with subungual melanomas will have tumors with a BRAF mutation. These mutations are acquired mutations which occur in the process of cells becoming cancerous, and not something you are born with.
  • Immunotherapy - Immunotherapy is a newer form of cancer treatment, and can be simplistically thought of as stimulating the immune system to fight off cancer. There are many individual types of treatment which fall under this category, many of which show promise in treating melanoma.
  • Radiation therapy - Radiation therapy is primarily used as a palliative treatment, to decrease pain, with these melanomas.
  • Clinical trials - There are many clinical trials in progress looking at newer and better ways to treat melanoma. If you find the thought of participating in a clinical trial frightening, keep in mind that every effective cancer treatment we now have was once studied in a clinical trial, and during the trial time, only those who were part of a clinical trial had the opportunity to use treatments which are now the standard of care.

Prognosis of Subungual Melanoma

Relative to other types of melanoma, subungual melanoma has a relatively poor prognosis, but this varies widely. Survival rates vary in studies from 16 to 80 percent, with the average 5-year survival considered to be around 50 percent.

What Should You Do If Your Are Diagnosed

If you've been diagnosed with a subungual melanoma, it's important to find physicians who are experienced with this disease. This is important for several reasons. Misdiagnosis is common and can lead to either inadequate treatment or unnecessary treatment. In addition, subungual melanomas are fairly uncommon and not all physicians have experience treating this disease either from a diagnosis (pathology), surgical (plastic surgery), or an oncology standpoint.

Getting a second opinion can be very important, and many people choose to get a second opinion at one of the larger National Cancer Instituted-designated cancer centers. Though results have not been specifically studied with subungual melanomas, it's been found that the outcome of some other types of cancer surgery are better when done at cancer centers which perform greater volumes of the procedures.

While having an excellent cancer care team is important, you remain the most important part of your cancer care team. Learn as much as you can about your cancer. Ask for help and accept help. Consider becoming involved in one of the online support communities in which you can communicate with others who have faced your challenge. And make it a point to be your own advocate in your cancer care. It does make a difference.

Sources:

Cochran, A., Buchanan, P., Bueno, R., and M. Neumeister. Subungual Melanoma: A Review of Current Treatment. Plastic and Reconstructive Surgery. 2014. 134(2):259-73.

Nguyen, J., Bakri, K., Nguyen, E., Johnson, C., and S. Moran. Surgical Management of Subungual Melanoma: Mayo Clinic Experience of 124 Cases. Annals of Plastic Surgery. 2013. 71(4):346-54.

Ohn, J., Choe, Y., Park, J., and J. Mun. Dermoscopic Patterns of Fungal Melanoychia: A Comparative Study with other Causes of Melanonychia. Journal of the American Academy of Dermatology. 2016 Oct 25. (Epub ahead of print).

Sinno, S., Wilson, S., Billig, J., Shapiro, R., and M. Choi. Primary Melanoma of the Hand: An Algorithmic Approach to Surgical Management. Journal of Plastic Surgery and Hand Surgery. 2015. 49(6):339-45.

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