What should I do about a new brown, non‑ulcerated lesion on the sole that appeared three days ago?

Urgent Evaluation Required for New Plantar Brown Lesion

Any new brown lesion on the sole that appeared suddenly requires immediate excisional biopsy to rule out acral lentiginous melanoma, as this location and presentation pattern are high-risk features that cannot be safely observed. 1, 2, 3

Why This Requires Urgent Action

Acral Melanoma is Uniquely Dangerous

• Acral lentiginous melanoma (ALM) accounts for only 5% of all melanomas but is the most common subtype on palms and soles, and is frequently diagnosed at advanced stages with worse prognosis. 4, 5
• The sole of the foot is a classic location for ALM, which can present as a brown macule or patch that may appear benign initially. 4, 6
• A progressive change in size—even over just 3 days—is a major warning sign that mandates immediate excision, not observation. 2, 7

Clinical Mimics Create Diagnostic Traps

• Plantar brown lesions can mimic benign conditions like hematomas, warts, or calluses, making clinical diagnosis unreliable without histopathology. 8, 6
• Even experienced clinicians cannot confidently exclude melanoma based on appearance alone in acral locations. 3, 8

What You Must Do Now

Immediate Excisional Biopsy is Mandatory

• Perform complete excisional biopsy with 2 mm margins of normal skin using a scalpel, including full thickness through subcutaneous fat. 1, 2
• The excision should be oriented longitudinally on the foot to facilitate potential future wide re-excision if melanoma is confirmed. 1
• Never use shave biopsy, punch biopsy, laser, or cryotherapy—these techniques prevent accurate Breslow thickness measurement and are considered substandard care for pigmented lesions. 1, 3

Before the Biopsy

• Photograph the lesion with a ruler for documentation. 1, 3
• Examine all regional lymph nodes (popliteal, inguinal) for enlargement, which would suggest possible metastatic disease. 2, 7
• Inspect the entire skin surface for additional suspicious lesions. 2

Critical Pathology Requirements

• Send the entire specimen for histopathologic examination—do not use frozen sections. 3
• The pathology report must include: confirmation of melanocytic nature, Breslow thickness, Clark level, presence/absence of ulceration, mitotic rate, and margin status. 1, 2, 7
• Request review by a dermatopathologist experienced in pigmented lesions if initial pathology is equivocal. 3

Common Pitfalls to Avoid

Do Not "Watch and Wait"

• A 3-day history of a new brown lesion on the sole is not reassuring—ALM can present with rapid onset and the timeline does not exclude malignancy. 2, 4
• Observation or serial photography is only appropriate for clearly benign, stable lesions in low-risk locations—not for new acral pigmentation. 3

Do Not Assume Trauma History Means Benign

• Even if the patient recalls minor trauma, hematomas on the sole can be clinically and dermoscopically indistinguishable from melanoma in situ. 8
• Without adequate physical trigger or improvement over 1-2 weeks, excision is mandatory. 8

Do Not Perform Partial Sampling

• Incisional or punch biopsy is only acceptable for very large lesions (>3 cm) where complete excision would cause significant morbidity, and should only be done by specialists in multidisciplinary melanoma teams—not in primary care. 1, 3
• Partial sampling risks missing the thickest, most invasive component and prevents accurate staging. 3

If Melanoma is Confirmed

• Wide re-excision with margins of 0.5-2 cm based on Breslow thickness will be required. 3
• Sentinel lymph node biopsy should be considered for lesions ≥0.8 mm thickness or with ulceration. 2
• Refer immediately to a multidisciplinary melanoma team for definitive treatment planning. 3, 7

Bottom line: This lesion requires excisional biopsy within days, not weeks. The sole is a high-risk location, new onset is concerning, and intact skin does not exclude melanoma in situ or early invasive disease. 1, 2, 4