Subungual melanoma is skin cancer under a toenail or fingernail, which usually becomes visible on the thumb or big toe as a brown to black discoloration of the nail. Melanoma is a form of skin cancer that arises from melanocytes. These are the pigment cells of the skin. Many nail melanomas start with a brown or black discoloration of the nail. If you find brown or black vertical stripes on the nail bed, it is important to have this assessed by your doctor. But such a discoloration can also be caused by a large number of other factors, such as a bacterial infection with Pseudomans aeruginosa or a yeast infection with Candida. A bruise under the nail due to trauma is also possible, as is the use of medications, local skin conditions or due to systemic diseases. In people with dark skin, it can often even be regarded as a physiological phenomenon at an older age.
- Stripe or stripes under toenail or fingernail
- Subungual hematoma: cancer under the nail
- Who affects subungual melanoma?
- Causes of melanoma under the nail
- Risk factors for nail melanoma
- Recognizing subungual melanoma and symptoms
- Brown or black streak or spot under the nail
- Amelanotic melanoma
- Examination and diagnosis
- Hutchinson’s sign
- ABCDEF rule
- Subungual melanoma treatment
- Prognosis and life expectancy
Stripe or stripes under toenail or fingernail
A brown or black stripe or stripes under the toenail or fingernail may indicate subungual melanoma. Melanoma is a form of skin cancer that arises from melanocytes. A subungual melanoma is a variant of acrolentiginous melanoma, which is located on the palms of the hands and the soles of the feet, and under or around the nails. Subungual melanoma is usually found under the nail of a thumb or big toe, but any fingernail or toenail can be affected. The subungual melanoma is therefore located under the nail. It is often misunderstood and mistaken for an innocent deviation. A subungual melanoma has various manifestations . It may become visible as:
- a tumor;
- a longitudinal brown band in the nail (melanonycia striata), i.e. in the longitudinal direction; or
- a diffuse (widely varying) brown-black discoloration of the nail.
Subungual hematoma: bruising under the nail / Source: Drgnu23, Wikimedia Commons (CC BY-SA-3.0)
Subungual hematoma: cancer under the nail
A subungual melanoma must be distinguished from a subungual hematoma, the medical name for bruising under the nail. There must always be a corresponding history, such as bumps, an object falling on the nail, jogging/running, other trauma, the use of blood thinners, etc. If this is not the case, then the distinction from a subungual melanoma with a subungual melanoma difficult. A bruise under the nail moves as the nail grows. This is clearly not the case with melanoma.
Who affects subungual melanoma?
Subungual melanoma is a rare skin condition. Only about 1% of all melanomas in light-skinned people are subungual melanoma. It occurs in people of all ethnic backgrounds, regardless of their skin color. Skin melanoma is a relatively rare phenomenon in people with dark skin, but subungual melanoma is approximately equally common in all skin types. The literature shows that 20% of all melanomas in people with skin types V and VI (dark skin) are located under the nail, while in skin types I and II (light skin) this is only 1%. It is therefore the most common form of melanoma in deeply pigmented individuals. Subungual melanoma is most common in people between the ages of 40 and 70. Men and women are affected equally often.
Causes of melanoma under the nail
A subungual melanoma is a malignant proliferation of pigment cells that arises in the nail root of a fingernail or toenail. Hereditary predisposition and/or trauma, or injuries to the nail, may play a role in the development of subungual melanoma, but the precise cause has not yet been clarified as of 2023.
Risk factors for nail melanoma
The most important risk factor for the development of skin melanoma is excessive exposure to ultraviolet (UV) radiation, but this causal relationship has not yet been proven for subungual melanoma as of 2023. Risk factors include:
- have a dark skin color
- be older than 50 years
- history of trauma to the fingers or toes
- having an immunosuppressive disorder, such as HIV
Recognizing subungual melanoma and symptoms
How and how can you recognize a subungual melanoma?
Brown or black streak or spot under the nail
A subungual melanoma often starts as a brown band in the nail in the longitudinal direction (melanonycia striata), a solitary brown stripe. Over time (weeks to months), the brown (pigment) band becomes wider, especially at its proximal end (the edge that runs around the nail plate) and more irregular in pigmentation, including light brown and dark brown. A tumor or lump may also develop, which may ulcerate or bleed. Furthermore, nail dystrophy can occur, where the nail becomes thinner, cracks or deforms.
In half of the cases it concerns an amelanotic melanoma, in which no pigment is visible. A tumor or lump may form under the nail plate, which can lead to nail detachment (or onycholysis). It can sometimes look like a wart. It is usually painless, but an invasive tumor can displace underlying structures and cause severe pain.
Examination and diagnosis
If you have a brown or black discoloration under the nail, whether it is in the form of a dot, dot, spot, band or stripe under the nail, that does not grow out but remains present, then it is important to make an appointment with your doctor to have this assessed. It is important to rule out ‘nail cancer’.
With a melanoma, the so-called ‘Hutchinson’s sign’ may be present. This indicates a brown discoloration of the cuticle skin. This discoloration is caused by pigment from ingrowing melanoma cells. These spread from a subungual melanoma. But this is sometimes also the case with a hematoma. Therefore, the ‘Hutchinson’s sign’ is inconclusive; rather, it is an indication or clue.
The doctor can use the ABCDEF rule to distinguish a harmless dark discoloration of a nail from a subungual melanoma:
|A for ‘age’
|It occurs after the age of 40
|B for ‘brown’
|Brown-black line visible, >3 mm, irregular boundaries
|C for ‘change’
|Change in color or width or aspect of the nail plate, for example rapid development, growth or darkening
|D for ‘digit’ (number)
|Involvement of a single nail, especially the big toe, thumb or index finger
|E for ‘extension’
|Presence of pigmentation of the surrounding skin (see ‘Hutchinson’s sign’);
|F for ‘family’
|Dysplastic nevi (troubled moles) or melanomas run in the family
The gold standard for diagnosis of subungual melanoma is histological examination (tissue examination). A biopsy (a piece of tissue) is necessary to rule out melanoma. This is examined by the pathologist under the microscope.
Subungual melanoma treatment
A subungual melanoma must be surgically removed. This requires removing the melanoma with a certain margin. The distal phalanx (the end of the finger or toe) is often amputated. Sometimes the surgeon can leave part of the phalanx intact, provided the required margin (according to the treatment protocol) allows this. According to the literature, removing the local lymph nodes does not contribute to the chances of survival.
Prognosis and life expectancy
The outlook and life expectancy for subungual melanoma are worse than for other types of melanoma because it is often diagnosed at a late stage. People often wait too long to go to the doctor with complaints. The five-year survival rate for subungual melanoma can vary widely, from 16 to 87 percent, depending on how extensively the cancer has spread. As a general rule, the earlier the cancer is detected, the better the chances of effective treatment and survival. A person’s prognosis often depends on how deeply the tumor has invaded the skin. The deeper a tumor is, the less favorable the prognosis.
- Melanoma: symptoms, recognition, cause and treatment
- Bruise under the nail: causes of blue nail
- Blue nails or blue nail: causes and what to do?
- Cuticle inflammation (paronychia): symptoms and treatment
- Skin disorders AZ: symptoms, cause and treatment
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