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Melanoma arising in the nail matrix presenting as a longitudinal pigmented band; requires prompt evaluation to differentiate from benign causes of nail pigmentation.
Subungual melanoma is a rare but serious form of melanoma that originates in the nail matrix, the tissue responsible for producing the nail plate. It most commonly presents as a longitudinal melanonychia, a darkly pigmented band running the length of the nail from the cuticle to the free edge. Although it accounts for only one to three percent of all melanoma cases in lighter-skinned populations, it represents a disproportionately higher percentage of melanoma diagnoses in individuals with darker skin tones, including those of African, Asian, and Hispanic descent.
The condition most frequently affects the thumbnail or great toenail, though any digit may be involved. Because subungual melanoma closely resembles benign causes of nail pigmentation, including traumatic haematomas, fungal infections, and benign naevi of the nail matrix, diagnosis is often delayed. Early detection is critical, as prognosis worsens significantly with advanced-stage disease.
Subungual melanoma arises from the malignant transformation of melanocytes within the nail matrix. Unlike cutaneous melanomas elsewhere on the body, ultraviolet radiation exposure is not considered a primary causative factor, which helps to explain why it is more prevalent in sun-protected anatomical sites. The precise aetiology remains incompletely understood, though several contributing factors have been identified.
Risk factors associated with subungual melanoma include:
The hallmark presentation of subungual melanoma is a longitudinal pigmented band within the nail plate, known as longitudinal melanonychia. However, not all longitudinal melanonychia is malignant, and distinguishing benign from malignant causes requires careful clinical assessment and, in many cases, histopathological examination.
Features that raise concern for subungual melanoma include:
In some cases, subungual melanoma may be amelanotic, meaning it lacks visible pigmentation entirely. Amelanotic variants are particularly challenging to diagnose and may present solely as nail dystrophy, a non-healing lesion, or a mass beneath the nail plate.
A thorough clinical evaluation is the first step in the diagnostic process. The examining dermatologist will assess the morphology of the pigmented band, review the patient's medical and family history, and evaluate the affected digit for secondary changes such as Hutchinson sign or nail plate destruction.
Dermoscopy, the use of a handheld illuminated magnification device, is a valuable non-invasive adjunct that can improve the clinical assessment of nail pigmentation. Under dermoscopy, features such as irregular longitudinal lines, micro-Hutchinson sign (pigmentation of the cuticle visible only under magnification), and disruption of the parallel line pattern raise the index of suspicion for malignancy.
Definitive diagnosis requires histopathological examination of tissue obtained by nail matrix biopsy. The biopsy technique must sample the nail matrix directly, as the pigmented cells originate there rather than in the nail plate itself. Specimen processing and interpretation by a pathologist with experience in nail pathology is essential to ensure accuracy.
Once a diagnosis of subungual melanoma is confirmed, staging workup is performed in accordance with standard melanoma protocols. This typically includes sentinel lymph node biopsy for tumours with a Breslow thickness greater than one millimetre, as well as imaging studies to evaluate for regional or distant metastatic disease depending on clinical stage.
Treatment of subungual melanoma is determined by the stage of disease at the time of diagnosis. Surgical excision is the mainstay of treatment for localised disease.
Surgical Management
Historically, amputation of the affected digit at the most distal interphalangeal joint was considered the standard surgical approach. However, contemporary evidence supports digit-sparing surgery with wide local excision in selected cases of early-stage disease, particularly when tumour thickness is minimal and clear surgical margins can be achieved while preserving functional anatomy. The decision between amputation and digit-sparing excision is made on an individual basis, weighing tumour characteristics against functional and cosmetic considerations.
Sentinel Lymph Node Biopsy
Sentinel lymph node biopsy is recommended for tumours with a Breslow thickness exceeding one millimetre, or for thinner tumours with high-risk features such as ulceration or a mitotic rate greater than one per square millimetre. A positive sentinel node finding guides further surgical management and adjuvant therapy decisions.
Systemic Therapies
For advanced or metastatic subungual melanoma, systemic treatment options have expanded considerably in recent years. Immune checkpoint inhibitor therapy, including programmed death-1 (PD-1) inhibitors such as pembrolizumab and nivolumab, has demonstrated meaningful clinical benefit and is now a standard treatment option for advanced melanoma. For tumours harbouring a BRAF V600 mutation, targeted therapy with BRAF and MEK inhibitor combinations may also be employed.
It is worth noting that acral melanomas, a category that includes subungual melanoma, have a lower frequency of BRAF mutations compared to other melanoma subtypes. Molecular tumour profiling is therefore an important component of treatment planning for advanced disease, and management is best coordinated through a multidisciplinary oncology team.
Follow-Up and Surveillance
Long-term dermatological surveillance is essential following treatment for subungual melanoma. Follow-up schedules are tailored to the stage of disease and may involve clinical examinations every three to six months for the first several years, with periodic imaging as clinically indicated. Patients are also counselled on the importance of dermoscopic monitoring of the remaining nails and skin for new pigmentary changes.
Prompt evaluation by a dermatologist is recommended whenever a new or changing pigmented band is observed beneath a nail, particularly in adults. A band that is widening, darkening, becoming irregular, or spreading onto the surrounding skin warrants urgent assessment. Similarly, any nail dystrophy, unexplained bleeding, or non-healing lesion involving the nail apparatus should be brought to medical attention without delay.
Because subungual melanoma is frequently mistaken for a bruise, a fungal nail infection, or a benign pigmented naevus, many patients delay seeking evaluation. Awareness of the distinguishing features and a low threshold for professional assessment are key to improving outcomes. Early-stage subungual melanoma carries a significantly better prognosis than disease that has been allowed to progress, making timely diagnosis one of the most important factors in survival. At the Centre for Medical and Surgical Dermatology, Dr. Maksym Breslavets provides expert assessment of nail pigmentation changes. A referral from a family physician is typically required to access dermatology services.
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