What is the proper procedure for performing a punch biopsy on a suspected melanoma lesion on the sole of a patient's foot?

Punch Biopsy for Suspected Melanoma on the Sole: Avoid It

For a suspected melanoma lesion on the sole of the foot, you should NOT perform a punch biopsy—instead, perform a complete excisional biopsy with a 2-5 mm margin of normal skin and include subcutaneous fat. 1

Why Punch Biopsy Is Contraindicated for Suspected Melanoma

Punch biopsies are explicitly not recommended for melanoma diagnosis because they prevent accurate pathological staging and risk misdiagnosis from partial sampling. 1 The critical issue is that punch biopsies cannot capture the full thickness of the lesion (Breslow depth), which is the single most important prognostic factor and determines all subsequent treatment decisions including surgical margins and need for sentinel lymph node biopsy. 1, 2

• Punch biopsies create a 23-34% risk of finding residual tumor at wide local excision with pathologic upstaging, meaning your initial staging was wrong and treatment planning was compromised. 3
• The inability to assess maximum tumor thickness makes it impossible to determine appropriate excision margins (1 cm for ≤2 mm thickness vs. 2 cm for >2 mm thickness). 4
• Partial sampling risks missing the thickest portion of the lesion, leading to understaging and inadequate initial treatment. 1

The Correct Approach: Complete Excisional Biopsy

Perform a full-thickness elliptical excision that includes the entire lesion with a 2-5 mm clinical margin of normal skin laterally and a cuff of subcutaneous fat deep to the lesion. 1, 2

Technical Details for the Sole:

• Orient the ellipse parallel to skin tension lines when possible to facilitate re-excision if needed. 1
• Use a scalpel (never laser or electrocautery) to avoid tissue destruction that compromises histological assessment. 1
• Include subcutaneous fat in the deep margin—this is non-negotiable for accurate Breslow depth measurement. 1, 2
• Document the exact anatomic location and orientation in your operative note. 1

Special Considerations for Acral Melanoma

The sole is a high-risk location where melanoma presents differently than on other body sites. 5 Acral melanomas are often diagnosed late and have worse prognosis, making complete initial excision even more critical. 5

• Lesions >7 mm diameter on the sole warrant biopsy regardless of other features. 5
• Even smaller lesions (<7 mm) should be biopsied if they show marked irregularity in shape/color or the "parallel ridge pattern" on dermoscopy. 5
• The entire pigmented lesion must be removed to assess whether this represents melanoma in situ versus invasive disease. 1

When Punch Biopsy Might Be Acceptable (Rare Exceptions)

The ONLY scenario where punch biopsy is acceptable for melanoma is when complete excisional biopsy is truly not feasible due to anatomic constraints—and this decision should only be made by specialists within a multidisciplinary skin cancer team, NOT in primary care. 4

• If you must use punch biopsy (very large lesion, anatomically challenging site), target the clinically thickest or most raised portion of the lesion with a full-thickness punch. 4, 6
• Use the largest punch possible (≥4 mm) to maximize diagnostic yield. 6
• If the punch biopsy is inadequate for diagnosis or accurate microstaging, perform narrow margin excision before proceeding to definitive wide local excision. 4

Critical Pathology Requirements

Send the specimen with complete clinical information including patient age, sex, exact anatomic site, and clinical suspicion for melanoma. 1 The pathologist must be able to report:

• Breslow thickness to the nearest 0.1 mm (measured from granular layer to tumor base). 1
• Presence or absence of ulceration. 1, 4
• Clark level of invasion. 1
• Mitotic rate, regression, and margin status. 1

Common Pitfalls to Avoid

• Never perform a shave biopsy on suspected melanoma—shave biopsies have the highest rate of positive deep margins (significantly more than punch or excisional biopsy) and prevent accurate depth assessment. 3
• Never assume you can "just take a piece" to confirm the diagnosis first—this approach leads to understaging, incorrect treatment planning, and potentially compromised outcomes. 1
• Don't orient your excision incorrectly—a transverse incision when a longitudinal one is needed may necessitate skin grafting at re-excision. 1