What is the diagnosis and treatment for subungual melanoma (skin cancer under the nail)?

From the Guidelines

Subungual melanoma should be diagnosed and treated with a narrow excisional/complete biopsy with 1- to 3-mm margins that encompass the entire breadth of the lesion, and the nail plate should be sufficiently removed to expose the underlying lesion, as recommended by the guidelines of care for the management of primary cutaneous melanoma 1. When a biopsy of a suspicious nail lesion is performed, the nail matrix should be sampled, and biopsies of possible subungual melanomas should be carried out by practitioners skilled in biopsy of the nail apparatus. The condition typically presents as a dark streak or band in the nail that gradually widens, changes color, or extends into the surrounding skin (Hutchinson's sign), and other warning signs include nail deformity, splitting, bleeding, or pain.

Diagnosis and Treatment

• The preferred biopsy technique is a narrow excisional/complete biopsy with 1- to 3-mm margins that encompass the entire breadth of the lesion, and is of sufficient depth to prevent transection at the base 1.
• Partial/incomplete sampling (incisional biopsy) is acceptable in select clinical circumstances, such as facial or acral location, very large lesion, or low clinical suspicion or uncertainty of diagnosis 1.
• For suspicious subungual lesions, the nail plate should be sufficiently removed to expose the underlying lesion, and an excisional or incisional biopsy performed depending on the size of the lesion 1.
• Treatment primarily involves surgical removal of the affected area, which may range from partial nail removal to amputation of the digit depending on the depth and spread of the cancer, with wide local excision with appropriate margins being the standard approach, followed by possible sentinel lymph node biopsy to check for metastasis 1.

Prognosis and Prevention

• The prognosis depends largely on early detection, with 5-year survival rates dropping significantly once the melanoma has spread beyond the nail unit.
• Patients should seek immediate medical attention if they notice any unusual changes in their nails, particularly persistent pigmentation changes, and regular self-examination of nails is recommended, especially for those with darker skin tones who have a higher incidence of this condition.
• The role of amputation versus digit preservation has been debated, as has the level of amputation, with little or no prospective data available, but a recent study advocated amputation of the distal phalanx with a margin of normal-appearing skin 1.

From the Research

Definition and Characteristics of Subungal Melanoma

• Subungual melanoma is a rare but lethal form of melanoma that arises from the structures of the nail apparatus 2.
• It presents most commonly in older patients and at an advanced stage, with a poor prognosis strongly associated with the presence of nodal disease at diagnosis 2.
• The median age of patients with subungual melanoma is around 62.9 years, with a median tumour thickness of 4.5 mm 2.

Surgical Management of Subungal Melanoma

• Optimal surgical management of subungual malignant melanoma has been debated, with various studies suggesting different approaches 3.
• Amputation at the level of the interphalangeal joint or proximal has been described as appropriate surgical management for all stages of subungal melanoma 4.
• However, wide local excision can improve functional and aesthetic outcomes in cases of subungual melanoma in situ (SMIS), with similar success in rates of local recurrence and metastasis when compared to treatment by amputation 4.
• Conservative resections are warranted as resection level does not influence outcome when histologically free margins are obtained 3.

Treatment Outcomes and Prognosis

• Patients with subungual melanoma often experience delayed diagnosis and present with deep primary lesions, which can lead to a less favorable outcome 5.
• The 5-year overall survival rate for patients with invasive subungual melanoma of the toe is around 40%, compared to 72% for those with finger lesions 5.
• Sentinel lymph node biopsy should be considered to determine stage and prognosis, as the presence of nodal disease at diagnosis is strongly associated with a poor prognosis 2.
• Functional, non-amputative surgical management of in situ subungual melanomas can result in good functional outcomes and no evidence of local or distant recurrences 6.