Acral lentiginous melanoma - improving detection on the foot
- Ivan Bristow
- Jun 2
- 10 min read
Earlier in May I presented at the Primary Care 2025 conference asking the question how do we improve melanoma detection on the foot? May was melanoma awareness month but it's always good to remind colleagues about melanoma and the difficulties in recognising it early.
Understanding that foot melanoma is different
Melanoma on the foot is different from other cutaneous melanoma. Most melanoma on the trunk and legs are in areas which may receive intermittent sunshine. These lesions are typically superficial spreading and nodular subtypes of the disease.
On the soles, palms and in the nail unit the predominant subtype is acral lentiginous melanoma (ALM) accounting for the vast proportion of melanoma in this area [1]. It is suspected that this subtype is not related directly to sun exposure and represents a different presentation of the disease. Lesions here rarely are exposed to sunlight and the thickened plantar skin and nail plate provides significant UV protection [2]. Moreover, rates of ALM have not increased in the last 50 years, unlike melanoma in more sun exposed areas [3].
Why is acral lentiginous melanoma more of a problem?
ALM is unique as it occurs on any skin type from Fitzpatrick type 1 to type 6. So effectively a type of melanoma which affects all races. Proportionally, patients with skin of colour have significantly lower rates of melanoma generally in sun exposed areas due to the increased skin pigmentation affording significant sun protection so compared to patients with white skin, they have fewer melanoma. However, if they do develop melanoma, it typically is an ALM located on the palms and sole or in the nail unit with ALM rates accounting for up to 86.6% of melanoma in some Asian populations [4].
Location and Visibility
However, studies have shown that patients with melanoma present at a more advanced stage if they are located in non-visible areas, like the plantar surface [5, 6], consequently it is important for the clinician to ensure that all areas of the foot are checked.
Prognosis
Over the years it has been reported by many studies that ALM has a poorer prognosis when compared with other types of melanoma. The true picture is a little complicated and studies investigating this aspect have had conflicting results due to the smaller numbers of ALM and some studies lacking control of confounding variables [7]. This had led to calls for consideration for a separate prognostic staging system for acral lesions [8]. However, many studies over the years report poorer outcomes for ALM versus other melanoma sub-types [9, 10].
Further research into the location of ALM lesions has demonstrated that foot holds a particularly poor prognosis [11, 12] particularly when the ALM is located on the sole holding a poorer prognosis than ALM on the palms and in the nail unit [13].
Misdiagnosis
Delayed diagnosis often arises through misdiagnosis. Misdiagnosis of melanoma arising on the foot is a common theme in the literature. In a previous study, we uncovered a misdiagnosis rate for ALM specifically of 33% [14] compared with around 14% rate for melanoma elsewhere on the skin [15, 16] . Owing to its rarity and high variable presentation, more common benign diagnoses are made which include a range pathologies such as tinea pedis [14, 15, 17-19], onychomycosis [20] , warts [21] [22-24], haematoma [25, 26], paronychia [27], ingrowing toe nail [28-30], bacterial infection [31], ischaemia or necrosis [32] , blisters, ganglions, callus , benign tumours [33, 34] and ulceration [35-41].
ALM in skin of colour
ALM disproportionately affects individuals with skin of colour [10], with health disparities in disease incidence, morbidity, and mortality rates among racial and ethnic groups [42]. There have been many studies investigating this. Reasons include late presentation due to lack of awareness of the typical warning signs of skin cancer on the foot, delay through misdiagnosis [29] and later definitive surgical intervention. Grewal [43] also demonstrated that most educational materials online depicted skin cancer in white patients. Moreover, rarely do these feature nails, soles and palms. Patients of colour also have a decreased awareness regarding the personal risk of developing skin cancer [44].
Less Effective response to biological therapies
In recent years there have been major strides in effective treatments using new classes of drugs including targeted therapy and immunotherapies. Targeted therapies work by affecting specific mutations found in melanoma such as BRAF and NRAS. Although some ALM may carry these mutations, they tend to be less frequent than in superficial spreading melanoma [45]. Moreover, even if they demonstrate the mutation, ALM appears to have a lower clinical effectiveness [46].
My top tips for detecting suspicious lesions on the sole of the foot
As this brief blog reports ALM continues to be a challenge medically due to its later presentation, later diagnosis and reduced response to the most modern therapies when compared to melanoma elsewhere. Consequently, podiatrists are uniquely placed to monitor patients. Here are my top tips:
1. At the initial assessment - note and record absence of any pigmented lesions.
90% of ALM appear on clear skin (what dermatologists call “de Novo” meaning that ALM appears from nowhere) with only 10% arising in pre-existing lesions [47]. Therefore, at initial assessment if there are no pigmented lesions on the soles then record it in the notes so that if anything changes, you have a reference point. Taking a photograph is ideal as it allows later comparison (NICE Guidelines 2016 1.3.3).
2. The patient's skin type is irrelevant.
As mentioned earlier, ALM affects all races including darker skin types and so no-one should be above suspicion.
3. Inspect all areas of the foot.
Research shows that patients are not good at self-screening their skin, particularly their feet and so it is good practice to visualise all areas of the skin on the foot, including the nails and the less easily visualised areas like the backs of the heels and interdigitally where lesions may easily be missed.
4. Size is important.
Any discovered pigmented lesion over 7mm in diameter on the soles needs a proper assessment as a significant proportion of lesions of this diameter are melanoma [48].
5. A history of trauma does not rule out an ALM
Research has shown that many patients mistakenly believe that the lesion is traumatic in origin, and not malignant. This is because a sudden trauma to the foot can make the patient look at their foot for the first time in many years, coincidentally discovering the “new” lesion mistakenly attributing it to trauma and not as a cancer [49]
6. Dermoscopy can be helpful
For those practitioners particularly interested in skin, consider investing in a dermatoscope and dermoscopy training. Evidence shows that dermoscopy can significantly improve a podiatrists ability to detect acral melanoma using validated methods such as the ridges and furrows rule [50] and the BRAAF algorithm [51].
7. Anything that is unusual or you are concerned about, consider referring.
One of the main issues about ALM is delayed diagnosis is that suspicious lesions may not get referred as the practitioner is worried about wasting anyone's time. If you are not sure, refer back to the GP.
8. If unsure, use the CUBED acronym.
The cubed acronym is specifically designed to give practitioner confidence in when to refer a suspicious lesion on the foot and has been advocated in a number of papers [52-54]. Download it here .
9. Remember EFG!
If any lesion on the skin, regardless of colour, is elevated, firm and growing, it should be considered malignant until proven otherwise. Remember the acronym "E.F.G" – elevated firm and growing. See my previous blog on this topic.
10. Never attempt to biopsy a suspicious lesion!
As a UK registered podiatrist, if a lesion is suspected to be melanoma or any other type of skin malignancy it should be urgently referred to a specialist for assessment.
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