Subungual melanoma is a type of skin cancer that occurs under the fingernails. "Subungual" is the medical term for "under the nail."

In this article, we learn about subungual melanoma, which is only one type of cancer that affects the nails.

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Subungual melanoma is a cancer that specifically develops under the nails.

Melanoma is a cancer of the skin that begins in the melanocytes, which are cells that have skin pigments. Collections of melanocytes can form moles. Some moles are cancerous, but many are not.

Melanoma can be difficult to treat if it is not detected in its earliest stages, as it can spread to other organs.

Melanoma is usually the result of excess ultraviolet sun exposure, so most people identify melanoma on parts of the body where the sun hits, such as the face.

They may be less likely to suspect melanoma in other areas of the skin where it can occur. This includes melanoma under the fingernails, which is known as subungual melanoma.

This type of melanoma often resembles normal bruising of the nails and may be difficult to identify.

There are different types of nail-related melanoma. Subungual melanoma comes from the nail matrix, which is where keratin originates. Other nail-related cancers include ungula melanoma, which occurs underneath the nail plate, and periungual melanoma, which comes from the skin next to the nail plate.

According to the Journal of Foot and Ankle Research, an estimated 1.4 percent of all diagnosed melanoma cases are those that affect the fingernail, including subungual melanoma.

Subungual melanoma often starts as a brown or black streak under a toenail or fingernail. A person may mistake it for a bruise.

The main symptoms associated with subungual melanoma are the following:

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A bruised nail, and dark streaks or stains on the nail with no known cause, may be signs of subungual melanoma.
  • brown or black streaks in the nail without any known injury
  • streaks on the nails that increase in size
  • a bruise on the nail that will not heal or move up as the fingernail grows
  • fingernails or toenails that separate from the nail bed
  • darkening skin next to the nail
  • a nail that bleeds or develops a nodule
  • thinning, cracking, or distortion of the nail plate

One of the key indications of subungual melanoma is known as "Hutchinson's sign." This is when a person has a streak that extends from the tip of the nail down to the nail bed and into the cuticle.

Most cases of subungual melanoma occur in the thumbnail or big toenail. However, a person may experience subungual melanoma on any fingernail or toenail.

Subungual melanoma occasionally occurs without the distinctive pigmented streaks. In this instance, a person may experience the other symptoms that are associated with subungual infections, including changes to the nail itself, bleeding, and pain at the nail bed.

Having certain risk factors does not mean someone will get subungual melanoma, but it does mean they are more at risk for the condition and should be especially vigilant for early symptoms.

The most significant risk factor for subungual melanoma is prolonged exposure to the sun and ultraviolet light.

Other risk factors include:

  • having darker skin
  • being older than 50
  • having a history of trauma to the fingers or toes
  • having an immunosuppressive disorder, such as HIV

A doctor will conduct a physical assessment of the fingernail and ask a person questions about the lesions on the fingernail.

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To accurately diagnose a subungual melanoma, a biopsy may be taken and sent to a pathologist for assessment.

They may ask when the nail streaking began, how the nail has changed over time, and about any other relevant medical history.

Some of the conditions that may look similar to subungual melanoma include:

  • onychomycosis, which is fungal nail infection
  • paronychia, an infection of the nail bed
  • pyogenic granuloma, or overgrowths of nail tissue
  • squamous cell carcinoma

If a doctor suspects the condition could be subungual melanoma, they will take a biopsy of the nail matrix, as well as the nail bed.

A pathologist specializing in identifying cancerous cells will examine the nail cells to determine if they are cancerous and appear the way melanoma cells typically do.

If a doctor confirms the diagnosis is melanoma, they may order more tests to determine if the cancer has spread.

A doctor will then stage the melanoma, or categorize it based on how many cancerous cells are present and how the melanoma has spread.

The subungual melanoma may be melanoma "in situ," meaning the cells are pre-cancerous and have not yet developed into fully cancerous cells.

The most severe form of subungual melanoma is stage IV, where the cancer cells have spread to other organs.

Once a doctor has determined the extent of subungual melanoma, they will usually start treatment by removing the affected area surgically. This may include removing the entire fingernail or a portion of the finger.

If the cancer has spread to the lymph nodes or throughout the body, it may be too extensive to treat just by removing the affected area.

Following the surgical removal of the affected area, a doctor may recommend further therapies to prevent the subsequent spread of the cancer. These treatments may include chemotherapy and radiation.

However, radiation therapy is often used as a palliative type of therapy for people with melanoma. This means the treatment will reduce the pain from the spread of cancerous cells, but it may not cure the cancer itself.

According to the New England Journal of Medicine, a person waits an estimated 2.2 years from the onset of their symptoms until diagnosis of subungual melanoma. However, it is important to seek proper diagnosis, as soon as symptoms become noticeable.

As a general rule, the outlook for subungual melanoma is poorer than other melanoma types, as there is often a delay in diagnosis. The 5-year survival rate for subungual melanoma can vary greatly, from 16 to 87 percent, depending upon how extensively the cancer has spread.

As a general rule, the earlier the cancer is detected, the better the chance for effective treatment and survival.

A person's prognosis is often related to how deeply the tumor has invaded the skin. The deeper a tumor is, the deadlier subungual melanoma can be.