What is the appropriate workup and treatment for a suspected acral melanoma located between the toes?

Workup and Treatment of Acral Melanoma Between the Toes

Diagnostic Biopsy

For suspected acral melanoma between the toes, perform a complete excisional biopsy with 2-5 mm margins of normal skin extending down to subcutaneous fat—never use punch or shave biopsies for this location. 1, 2

Biopsy Technique Specifics

• Complete excisional biopsy is mandatory because partial sampling prevents accurate Breslow thickness measurement and risks understaging the tumor 1, 2
• Orient the excision along the long axis of the digit to facilitate subsequent wide local excision 1
• Include a cuff of subcutaneous fat in the specimen to ensure full-thickness assessment 1, 2
• Use a scalpel rather than cautery to avoid tissue destruction that compromises histological assessment 2
• Photograph the lesion before excision 1

Why Punch Biopsy is Contraindicated

• Punch biopsies make accurate pathological staging impossible and lead to incorrect diagnosis through sampling error 1
• The inability to assess maximum tumor thickness prevents determination of appropriate definitive excision margins 2
• Partial sampling risks missing the thickest portion of the lesion, resulting in understaging and inadequate initial treatment 2

Incisional Biopsy Exception

• Incisional or punch biopsy is occasionally acceptable for acral melanoma only within a multidisciplinary skin cancer team setting when complete excision is not immediately feasible 1

Required Pathology Information

Clinical Information to Provide

• Patient age and sex 2
• Exact anatomic location (between toes, specify which toes) 2
• Lesion history and clinical suspicion for melanoma 1, 2
• Relevant previous history 1

Essential Pathology Report Elements

• Breslow thickness in millimeters (maximum depth of invasion) 1, 2
• Presence or absence of ulceration 1, 2
• Clark level of invasion 1, 2
• Mitotic rate (number per area of greatest mitoses in vertical growth phase) 1, 2
• Surgical margin status (peripheral and deep margins in millimeters) 1, 2
• Presence and extent of regression 1
• TNM and AJCC staging 1

Definitive Surgical Treatment

Following confirmed diagnosis, perform wide local excision with 1-2 cm margins for invasive melanoma, though narrower margins may be necessary between toes to preserve function. 1

Margin Guidelines by Breslow Thickness

• Melanoma in situ: 0.5-1.0 cm margins 1
• Invasive melanoma ≤2 mm thick: 1 cm margins 1
• Invasive melanoma >2 mm thick: 2 cm margins (though modifications needed for digits) 1
• Excision depth should extend to (but not including) the fascia 1

Anatomic Considerations for Acral Sites

• Margins may need to be narrower than standard recommendations to preserve function at anatomically constrained sites like between toes 1
• For tumors on digits where adequate margins cannot be achieved, amputation may be necessary 3, 4
• The goal is histologically negative margins while maintaining maximum function 1

Sentinel Lymph Node Biopsy

Perform sentinel lymph node biopsy (SLNB) before wide excision and in the same operative setting whenever possible for invasive melanomas meeting criteria. 1

SLNB Indications

• SLNB should be performed by skilled teams in experienced centers 1
• Consider for melanomas >1 mm thickness or with high-risk features 1
• If sentinel node is positive, complete lymph node dissection of the regional basin is indicated 1, 4

Staging Workup

Initial Staging for Localized Disease

• Physical examination focusing on tumor satellites, in-transit metastases, and regional lymph nodes 1
• Chest X-ray 1
• Laboratory tests: Complete blood count, LDH, and alkaline phosphatase 1
• Ultrasound of regional lymph nodes for melanomas >1 mm thickness 1
• Ultrasound of abdomen only if clinically indicated 1
• PET scanning is not useful for initial staging of clinically localized melanoma 1

Adjuvant Therapy Considerations

Radiation Therapy

• Consider adjuvant radiotherapy if re-excision is not feasible and margins are inadequate 5
• May be indicated for head/neck melanomas where re-excision would be cosmetically disfiguring, though less relevant for interdigital location 5

Systemic Therapy

• No standard adjuvant therapy currently proven to improve overall survival for high-risk melanoma 1
• High-dose interferon prolongs disease-free survival but not overall survival, and must be balanced against toxicity 1

Critical Pitfalls to Avoid

• Never perform shave or punch biopsies for suspected acral melanoma—this is the most common error leading to understaging 1, 2
• Do not perform partial removal of pigmented lesions between toes, as this creates diagnostic confusion and prevents accurate staging 1
• Avoid prophylactic excision of benign-appearing nevi without suspicious features 1
• Ensure the pathologist receives complete clinical information, as acral melanomas have unique characteristics requiring specialized assessment 2, 6

Prognosis Considerations

• Acral melanomas often present at more advanced stages and carry poorer prognosis than other melanoma subtypes 6, 7
• Five-year survival for Stage I acral melanoma on digits is approximately 27%, compared to 63% for plantar/palmar lesions 8
• Early diagnosis through complete excisional biopsy is critical for improving outcomes 6, 7

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