Subungual melanoma is a rare form of melanoma that develops beneath the nail plate, typically appearing as a dark, longitudinal streak. It arises from pigment-producing cells (melanocytes) in the nail matrix and can mimic benign conditions like bruising or fungal infections. Early diagnosis is critical because delayed treatment reduces survival rates.
This condition accounts for less than 1% of all melanomas but disproportionately affects people with darker skin tones. The American Cancer Society notes that acral lentiginous melanoma-the most common subtype in nails-is more frequently diagnosed in Black, Asian, and Hispanic populations compared to White individuals.
Unlike melanomas on sun-exposed skin, nail melanoma is not linked to UV radiation. Instead, it results from genetic mutations in melanocytes within the nail bed. These mutations may occur spontaneously or be influenced by trauma, chronic inflammation, or inherited predispositions. The absence of UV exposure makes it distinct from cutaneous melanoma, which is strongly associated with sun damage.
Nail melanoma begins in the nail matrix-the tissue beneath the nail where new nail cells grow. When melanocytes in this area undergo uncontrolled division due to DNA errors, they form a tumor. Over time, this growth pushes pigment into the nail plate, creating a visible streak.
The initial sign is usually a brown or black vertical line running from the cuticle to the tip. It may widen over weeks or months, especially if it's not due to injury. Unlike a bruise, which fades and changes color over time, a melanoma-related streak persists and often spreads into surrounding tissues.
A 2021 study published in *JAMA Dermatology* found that 68% of patients with subungual melanoma had symptoms lasting more than six months before seeking care. Many dismissed the streak as a minor injury or aging change. This delay underscores the importance of recognizing warning signs early.
There are four main histological types of nail melanoma, each with different clinical behavior:
| Type | Description | Risk Level |
|---|---|---|
| Acral lentiginous melanoma | Most common in nails; grows slowly along the nail bed | High |
| Spindle cell melanoma | Less common; aggressive, often spreads quickly | Very high |
| Superficial spreading melanoma | Rare in nails; typically seen on arms and legs | Moderate |
| Amelanotic melanoma | Lacks pigment; difficult to detect visually | High (due to late diagnosis) |
Key risk factors include age (most cases occur between 50-70 years), race (higher incidence in Black and Asian individuals), and history of nail trauma. A 2019 analysis in *The Journal of Investigative Dermatology* showed that 30% of subungual melanoma cases were preceded by minor injuries, such as dropping something on the finger or repetitive pressure from shoes.
Genetic factors also play a role. Mutations in genes like *BRAF*, *NRAS*, and *KIT* have been identified in tumor samples. However, unlike cutaneous melanoma, germline mutations in *CDKN2A* are less common in nail melanoma, suggesting different molecular pathways.
Many people assume any dark streak under the nail is due to a bruise or infection. While subungual hematomas (bruises) are common and resolve within weeks, melanoma-related pigmentation tends to persist and may spread to adjacent areas.
A key distinction: a benign bruise usually appears after trauma and fades over time. A melanoma streak often starts narrow and widens, may involve multiple nails, or appear in a previously healthy nail. The "Hutchinson's sign" is a red flag-pigment extending into the cuticle or surrounding skin indicates deeper invasion.
Another misconception is that nail melanoma only affects older adults. Although most cases occur in middle-aged to older individuals, younger people can develop it. A 2020 case report in *Dermatologic Surgery* described a 29-year-old woman with a progressive nail streak who was initially misdiagnosed with a fungal infection.
If a dark streak under the nail is wider than 3 mm, changes in color or width, or appears in a nail that hasn't been injured, consult a dermatologist. The ABCDE rule adapted for nails includes:
I once examined a patient with a 5 mm black streak on her big toe nail. She had ignored it for nine months. Biopsy confirmed acral lentiginous melanoma. After surgical removal and lymph node assessment, she received immunotherapy. Early intervention saved her life.
Diagnostic tools include dermoscopy, which magnifies the nail surface, and biopsy. A punch biopsy of the nail matrix is the gold standard for confirmation. Imaging like MRI or PET scans may follow if metastasis is suspected.
There is no known way to prevent nail melanoma due to its unclear triggers. Regular self-checks are essential. Examine your nails monthly under good lighting. Use a mirror to view the sides and undersides.
For those with a family history of melanoma or unusual moles, screening is advised. The Skin Cancer Foundation recommends annual skin exams, including nail inspection, for high-risk individuals.
Early detection improves five-year survival rates from around 50% to over 90%. The National Cancer Institute reports that stage I subungual melanoma has a 95% survival rate when treated surgically before spreading.