Nail cancer most commonly appears as a dark, vertical stripe running the length of the nail. In about 65% of cases, this brown-to-black pigmented band on a single nail is the first visible sign. The stripe typically exceeds 3 mm in width and may have blurry or irregular edges, especially where it meets the cuticle. But not all nail cancers look the same, and some don’t produce a dark line at all.
The Dark Stripe: Most Common Sign
The hallmark of subungual melanoma, the most serious type of nail cancer, is a longitudinal band of pigment stretching from the base of the nail to the tip. It can range from light brown to jet black. What makes it suspicious is its behavior over time: the band tends to widen, especially near the cuticle, and its borders become increasingly irregular. A harmless pigmented streak, which many people have, usually stays uniform in color and width for years.
One particularly telling sign is called Hutchinson’s sign. This is when brown or black pigment spills beyond the nail itself onto the surrounding skin of the cuticle or the sides of the finger. That extension of color from the nail band onto nearby skin is a strong indicator of melanoma and should prompt an urgent evaluation.
How It Differs From a Bruise Under the Nail
A blood blister under the nail (subungual hematoma) can look alarming, but it behaves very differently from cancer. A hematoma appears quickly, usually within hours of an injury you can recall. It looks like a dark bruise or smudge rather than a defined stripe. Most importantly, it moves. Fingernails grow at roughly 3.5 mm per month, so a bruise gradually shifts toward the tip of the nail and eventually grows out when you trim it. Toenails grow more slowly, around 1.6 mm per month, so a bruise on a toenail can linger for many months.
Melanoma, by contrast, grows slowly and stays anchored in place. The dark band doesn’t migrate forward with the nail. If a discoloration hasn’t budged after several months, or if it appeared without any trauma, that’s a reason to get it checked.
Squamous Cell Carcinoma of the Nail
Not all nail cancer is melanoma. Squamous cell carcinoma is actually the most common malignant tumor of the nail unit, and it looks quite different. Instead of a dark stripe, it often shows up as a warty or rough growth on the exposed nail bed, sometimes with the nail lifting away from the skin underneath. In more advanced stages, the area can erode and ulcerate, forming a scab or oozing. It may also appear as redness under or around the nail, or as a stubborn sore that won’t heal.
Because it can mimic a wart, a fungal infection, or chronic nail trauma, squamous cell carcinoma of the nail is frequently misdiagnosed for months or even years before being correctly identified. Any persistent, unexplained change in a single nail that doesn’t respond to treatment deserves a closer look.
What Happens as Nail Cancer Progresses
Early nail melanoma may look like nothing more than a thin, faint line. Over time, the band darkens, widens, and develops uneven coloring with multiple shades of brown and black. The nail plate itself can begin to thin, crack, or become distorted. In the vertical growth phase, when the tumor is invading deeper tissue, ulceration can occur. At that point, the nail may partially or fully break down, and there may be bleeding or a visible mass beneath or around the nail.
These later signs represent a more advanced cancer that is harder to treat. That’s why catching the early stripe matters so much.
Who Is Most at Risk
Nail melanoma accounts for a much larger share of all melanoma diagnoses in people with darker skin tones. For Black, Asian, Hispanic, and Native American populations, melanoma of the nail, palm, or sole represents a disproportionate percentage of melanoma cases compared to white populations, where sun-exposed skin melanomas dominate. This isn’t because nail melanoma is more common in these groups in absolute numbers, but because other types of melanoma are far less common, making nail melanoma a relatively bigger concern.
The cancer most often strikes the thumb or the big toe, and it tends to affect the dominant hand. It’s more frequently diagnosed in people over 50, though it can occur at any age.
The ABCDEF Screening Guide
Dermatologists use a six-part checklist specifically designed for nail pigment bands. It’s a useful framework for understanding which features raise concern:
- A (Age and ancestry): Peak incidence in the 50s through 70s, with higher relative risk in African American, Asian, and Native American populations.
- B (Band characteristics): Brown-to-black color, breadth of 3 mm or more, or a blurred border.
- C (Change): Any evolution in the band’s width, color, or shape over time, or failure to improve after treatment for another suspected cause.
- D (Digit): Thumb, big toe, or index finger are more commonly affected, particularly on the dominant hand.
- E (Extension): Pigment spreading onto the skin around the nail (Hutchinson’s sign).
- F (Family history): Personal or family history of melanoma.
No single factor is diagnostic on its own. But the more criteria that apply, the more urgently a biopsy is needed.
How Nail Cancer Is Confirmed
Visual examination alone cannot confirm or rule out nail cancer. A biopsy of the nail matrix, the tissue at the base of the nail where growth originates, is the only definitive way to diagnose it. For a pigmented band, the typical approach involves lifting the nail plate, locating where the band originates, and taking a thin shave of tissue from that spot. Punch biopsies, which remove a small cylinder of tissue, are also used depending on the location and size of the suspicious area.
The procedure is done under local anesthesia. There can be some temporary nail distortion afterward, but when the biopsy is oriented properly along the nail matrix, scarring is usually minimal. The tradeoff is well worth it: catching melanoma while it’s still confined to the surface layer of skin dramatically improves outcomes, while delays of months or years, which are unfortunately common with nail melanoma, allow the cancer to invade deeper tissues.