Mole on Sole of Foot: Acral Melanoma Risk and Monitoring

The sole of the foot is acral skin — thicker than skin elsewhere, ridge-patterned (visible as fingerprint-like lines), and not directly UV-exposed.

UV is not the primary driver of acral melanoma. The cause is not fully understood — possibly chronic mechanical pressure, genetic factors, or other unknown drivers. What's clear is that:

Acral melanoma rates are similar across ethnic groups in absolute terms, but it represents a much higher fraction of total melanoma in people of Asian, Black, and Hispanic ancestry (because they have lower rates of sun-driven melanoma elsewhere).

In light-skinned populations, ALM accounts for about 1-3% of all melanomas. In Asian populations, 30-40%. In Black populations, 60-70%.

Diagnosis is often delayed because lesions look like bruises, blood blisters, fungal infections, or warts.

The practical implication: any persistent pigmented lesion on the sole, palm, or under a nail deserves a lower threshold for evaluation than the same lesion elsewhere. The 'ugly duckling' on the sole gets more attention than the same lesion on the calf.

Most sole pigmentation is benign:

Acral nevus. Brown spot, often present since childhood, stable, well-defined borders. Common.

Punctate pigmentation. Multiple small brown dots on the sole, often genetic. Stable. Benign.

Blood blister (subcorneal hematoma). Dark red or purple, develops after pressure or friction (new shoes, long walks). Resolves in 1-2 weeks.

Plantar wart with thrombosed capillaries. Verrucous lesion with small black dots representing clotted vessels. Caused by HPV.

Fungal pigmentation. Some fungal infections cause discolouration. Usually with associated scaling or itching.

Post-inflammatory hyperpigmentation. After injury, blisters, or eczema patches.

The distinction between these and acral melanoma often requires close visual inspection plus dermoscopy. Self-assessment is harder for soles than for skin elsewhere because the ridge pattern complicates the visual appearance.

Dermoscopy of acral skin reveals two distinct patterns of pigmentation:

Parallel furrow pattern: pigment follows the grooves between the skin ridges. Benign acral nevus pattern.

Parallel ridge pattern: pigment follows the ridges themselves (the raised lines, not the grooves). Strong indicator of acral melanoma. Sensitivity around 86%, specificity around 99% for acral melanoma when present.

With the naked eye, the difference can sometimes be seen by examining the lesion under good lighting and asking: does the pigment trace through the ridges (concerning) or settle into the grooves between them (reassuring)?

For accurate assessment, a dermatologist with a dermatoscope should examine any persistent acral pigmented lesion. The parallel ridge pattern alone is sufficient to prompt biopsy in most clinical practices.

Within 2-4 weeks if any:

New sole mole that has appeared in the past 6-12 months.

Growing sole mole.

Irregular borders or multiple colours.

Diameter over 6-7mm.

Lesion that doesn't fit the surrounding ridge pattern.

Within 1-2 weeks if any:

Dark spot on sole that has not resolved in 4-6 weeks (longer than a typical bruise/blood blister).

Lesion with parallel ridge pattern visible to naked eye.

Ulceration, bleeding, or non-healing.

Lesion in someone over 50 of Asian, Black, or Hispanic ancestry (higher prior probability of ALM).

Personal history of melanoma anywhere.

For any persistent acral pigmented lesion in someone of any ancestry, a dermatology evaluation with dermoscopy is the right action. The lesion does not need to look 'classically melanoma' to deserve a look — many ALMs are subtle.

Different molecular profile. ALM has different mutations than cutaneous melanoma — fewer BRAF mutations, more KIT mutations. Some targeted therapies that work for cutaneous melanoma don't work as well for ALM.

Response to immunotherapy is generally lower in ALM than in cutaneous melanoma, although this varies and individual responses can be excellent.

Surgery is anatomically more challenging on soles, especially for advanced lesions, because preserving foot function is a priority.

Reconstruction after wide excision may require skin grafts.

This is one of the cancers where early diagnosis is the biggest single predictor of good outcomes. The toolset for advanced ALM is more limited than for advanced cutaneous melanoma, so catching it at in-situ or stage I is especially important.

Monthly self-exam should include soles as part of full-body coverage. This is one of the harder areas to check on yourself; consider:

Sitting and using a hand mirror.

Asking a partner or family member.

Using your phone camera to photograph soles.

During a shower or bath, when feet are clean and elevated.

For any sole mole, photograph with a coin or ruler for scale and the date. Repeat every 3-6 months. Compare. Subtle change is hard to detect without baseline photos.

What to look for:

New lesions appearing.

Existing lesions changing in size, shape, or colour.

Dark stripes that look unlike the surrounding ridge pattern.

Lesions that don't fade like a normal bruise.

Ulceration or non-healing patches.

For people in higher-risk groups (Asian, Black, Hispanic ancestry; prior melanoma; family history), 6-monthly dermatology examination of soles, palms, and nails is reasonable. A dermatologist will examine with dermoscopy in 5-10 minutes.