Melanomas are a type of cancer that develop from melanocytes, which are the cells that produce pigment, generally in the skin. However, they can also develop in the eye and possibly other parts of the body. Nail unit melanoma is a rare variant of cutaneous melanoma (or melanoma of the skin) which develops underneath the fingernail.
The nail is composed of four main structures: nail plate, nail matrix, nail bed, and periungual soft tissues. The nail plate, also known as the nail body, is the protective outer visible layer of the nail that is made up of hardened, tightly packed keratin cells. The nail plate is produced by the nail matrix, which sits at the base of the nail. The nail bed is the pink, soft tissues that lie beneath the nail plate that contains the nerves and blood vessels required for nail growth. Periungual soft tissues, including the eponychium (cuticle), nail folds, and hyponychium, are supportive tissues surrounding the nail that provide support and protection to the nail.
In most cases, a nail unit melanoma develops in the nails of the thumb or the big toe. However, it can develop in any nails of the fingers and toes.
Nail unit melanoma tends to be diagnosed equally among the sexes, and is most common in people between the ages of 50-70. However, anyone can develop this disease at any age.
Types of Nail Unit Melanoma
There are three primary types of nail unit melanoma which are classified by the types of cells they develop from.
Subungual Melanoma
Subungual melanomas are the most common type of nail unit melanoma, and they develop from the nail matrix portion of the nail. These cancers are often associated with trauma, and therefore are often diagnosed at a late stage of disease. Subungual melanomas can be aggressive, but can have a good prognosis when caught early.
Ungual Melanoma
Ungual melanomas are a less common subtype of nail unit melanomas, and they develop from underneath the nail plate. These cancers are often associated with trauma, and therefore are often diagnosed at a late stage of disease. Ungual melanomas can be aggressive, but can have a good prognosis when caught early.
Periungual Melanoma
Periungual melanomas are a less common subtype of nail unit melanomas that develop from the periungual soft tissues surrounding the nail. These cancers are often associated with trauma, and therefore are often diagnosed at a late stage of disease. Periungual melanomas can be aggressive, but can have a good prognosis when caught early.
Treatment
If a nail unit melanoma is detected, it will be staged and graded based on size, metastasis (whether the cancer has spread to other parts of the body) and how the cancer cells look under the microscope. Staging and grading helps your doctors determine the best treatment for you.
Cancers can be staged using the TNM staging system:
- T (tumour) indicates the size and depth of the tumour.
- N (nodes) indicates whether the cancer has spread to nearby lymph nodes.
- M (metastasis) indicates whether the cancer has spread to other parts of the body.
This system can also be used in combination with a numerical value, from stage 0-IV:
- Stage 0: this stage describes cancer cells in the place of origin (or ‘in situ’) that have not spread to nearby tissue.
- Stage I: cancer cells have begun to spread to nearby tissue. It is not deeply embedded into nearby tissue and had not spread to lymph nodes. This stage is also known as early-stage cancer.
- Stage II: cancer cells have grown deeper into nearby tissue. Lymph nodes may or may not be affected. This is also known as localised cancer.
- Stage III: the cancer has become larger and has grown deeper into nearby tissue. Lymph nodes are generally affected at this stage. This is also known as localised cancer.
- Stage IV: the cancer has spread to other tissues and organs in the body. This is also known as advanced or metastatic cancer.
Cancers can also be graded based on the rate of growth and how likely they are to spread:
- Grade I: cancer cells present as slightly abnormal and are usually slow growing. This is also known as a low-grade tumour.
- Grade II: cancer cells present as abnormal and grow faster than grade-I tumours. This is also known as an intermediate-grade tumour.
- Grade III: cancer cells present as very abnormal and grow quickly. This is also known as a high-grade tumour.
Once your tumour has been staged and graded, your doctor may recommend genetic testing, which analyses your tumour DNA and can help determine which treatment has the greatest chance of success. They will then discuss the most appropriate treatment option for you.
Treatment is dependent on several factors, including location, stage of disease and overall health.
Treatment options for nail unit melanomas may include:
- Surgery, potentially including:
- Wide local excision of the tumour and a healthy margin of tissue around it.
- Moth’s micrographic surgery (specialised surgery that removes thin layers of cancer in stages until completely removed).
- Lymphadenectomy.
- Amputation of affected finger or toe (in rare cases).
- Chemotherapy.
- Radiation therapy.
- Immunotherapy.
- Targeted therapy.
- Clinical trials.
- Palliative care.
For more information on the treatment options, please refer to the Rare Cancers Australia treatment options page.
Risk factors
While the cause of nail unit melanoma remains unknown, the following factors may increase the risk of developing the disease:
- Certain genetic mutations.
- Family and/or personal history of melanoma.
- Being of African, Japanese, Chinese, and/or Native American heritage.
Unlike most melanomas, UV exposure has not been identified as a risk factor of this disease.
Not everyone with these risk factors will develop the disease, and some people who have the disease may have none of these risk factors. See your general practitioner (GP) if you are concerned.
Early symptoms
Symptoms of a nail unit melanoma may include:
- A narrow brown-black band that extends the length of the nail.
- Irregular borders of bands in nail.
- Hutchinson sign (band extends into skin surrounding the nail).
- Nodulation, ulceration and/or bleeding of lesion.
- A mass under the nail plate.
- Thinning, cracking, and/or distortion of the nail plate.
- Painful lesion.
ABCDEF of Nail Unit Melanoma
To assist in the assessment of a suspected nail unit melanoma, physicians have made up an ABCDEF mnemonic:
- A – Age (50-70); African, Japanese, Chinese, and/or Native American heritage.
- B – Brown-black pigmented band that is greater than 3 millimetres and blurred borders.
- C – Change or lack of change despite treatment of nail band or lesion.
- D – Digit most commonly involved (big toe and thumb).
- E – Extension of pigment into skin surrounding the nail (also known as Hutchinson sign).
- F – Family or personal history of melanoma.
Not everyone with the symptoms above will have cancer, but see your general practitioner (GP) if you are concerned.
Diagnosis/diagnosing
If your doctor suspects you have a nail unit melanoma, they may order the following tests to confirm the diagnosis and refer you to a specialist for treatment.
Physical examination
Your doctor will collect your overall medical history, as well as your current symptoms. Following this, they may examine your body to check for any abnormalities.
Dermascopic Examination (Onychoscopy)
Dermoscopy is a non-invasive procedure used to examine lesions of the skin, also known as cutaneous lesions. This procedure involves the use of a high-quality magnifying lens with a powerful light (also known as a dermatoscope) to examine features of suspicious skin lesions, such as colour, morphology (shape and size), ulcerations, and other abnormalities. Further testing may be required if this examination shows anything unusual.
Imaging & blood tests
The doctor will take images of your body using magnetic resonance imaging (MRI), a computed tomography scan (CT scan), and/or positron emission tomography (PET scan), depending on where it is suspected the cancer is. The doctor may also look at other parts of the body and looks for signs of metastasis. Additionally, a blood test may be taken to assess your overall health and help guide treatment decisions.
Biopsy
Once the location(s) of the cancer has been identified, the doctor will perform a biopsy to remove a section of tissue using a needle. The tissue sample will then be analysed for cancer cells. This can be done by a fine needle aspiration (FNA), excisional biopsy, incisional biopsy, punch biopsy, or lymph node biopsy. This sample will then be sent to the laboratory and analysed for cancer cells.
Prognosis (Certain factors affect the prognosis and treatment options)
While it is not possible to predict the exact course of the disease, your doctor may be able to give you a general idea based on the rate and depth of tumour growth, susceptibility to treatment, age, overall fitness, and medical history. Generally, early-stage nail unit melanoma has a better prognosis and survival rates. However, if the cancer is advanced and has spread, the prognosis may not be as good and there may be a higher risk of cancer recurrence. It is very important to discuss your individual circumstances with your doctor to better understand your prognosis.
References
Some references are to overseas websites. There may be references to drugs and clinical trials that are not available here in Australia.