Melanoma is the fifth most common skin cancer that can arise anywhere on the skin including the feet. The soles of the feet (like the nails) are rarely subjected to UV light – a frequently documented cause of melanoma, which has led to the idea that melanoma in these areas might arise because of an alternative cause such as trauma. This blog investigates the current evidence for this hypothesis asking does trauma cause melanoma on the foot?
How common is melanoma on the feet?
There are around 200,000 cases of melanoma reported worldwide annually. It is the fifth most common cancer in the UK, accounting for around 4% of all new cancer cases and more cancer deaths than all other skin cancers combined [NICE, 2022]. A small but significant number of melanoma arise on the palms soles and within the nail unit. Such lesions are termed “acral” melanoma (AM). Cancer research UK report that between 5% and 10% of people in UK diagnosed with melanoma have acral melanoma.
Worldwide acral melanoma account for approximately 2% of all melanomas (1.5% for plantar acral melanomas), with an incidence of approximately 1.8 cases per million population [1]. Acral melanoma is relatively rare, however, it is the predominant subtype in Asian and black populations [2-5]. This is largely due to the much lower rates of UV related cutaneous melanomas in these ethnic groups. Overall, there is a similar incidence of acral melanoma in all ethnicities [4, 5] but more non-acral melanomas occur in white skin populations [4].
It is important to highlight that melanoma situated on the foot has a poorer prognosis than melanoma elsewhere. The predominant histological subtype being acral lentiginous melanoma (ALM). Their lack of visibility to the patient leads to a later diagnosis as these lesions are frequently presented late to clinicians and also, they are frequently misdiagnosed as benign dermatoses [1].
What causes melanoma in acral areas?
Research investigating the cause of acral lesions is in short supply. However, histological studies of excised AM have shown that it displays genetic mutations distinct from melanoma in sun exposed sites [3, 5, 6], and classic risk factors such as UV sun exposure seem less relevant [7]. This suggests other causal factors may be involved. A familial history has not been reported [8] although patients with acral melanoma had a secondary cancer and family history of cancer more often than patients with other melanoma subtypes, so there may be some genetic factors involved [5]. But could trauma or ongoing mechanical stress to the sole of the foot be a factor?
Trauma and melanoma
The role of trauma and mechanical stress in acral melanoma has been debated since it was first suggested in 1913 [9]. As the plantar surface of the foot is not subject to sun exposure it has been speculated that trauma or mechanical stress may be a causative factor. Of course, investigating this as a theory is difficult. Research retrospectively interviewing patients has shown they may report a history of trauma to an area prior to melanoma diagnosis [10]. However, this does not imply trauma as causation - coincidental trauma such as a cut or injury may have simply led to the patient becoming aware of a melanoma already in situ. This is typified by the most prominent case of nail melanoma. Bob Marley, the world-famous reggae artist died of a nail unit melanoma on his foot. As various news sources report this was only discovered coincidentally. Examination of a football injury to his foot led to the discovery of the cancer by a doctor.
What evidence of trauma as a cause exists?
Theoretically, tissue trauma and subsequent chronic inflammation could facilitate metastases by attracting existing metastatic cells to the area or by stimulating already present cells to proliferate at the site of trauma [11, 12].
Studies have mostly been conducted in Asian populations and show that the majority of plantar acral melanomas occur on higher weightbearing areas such as the forefoot, lateral midfoot and heel [4, 7, 12-15] with the majority occurring under the heel. These areas are subject to high pressures and shearing stress. Much fewer acral melanoma are reported in the arch area where the skin is under less pressure.
When comparing melanomas on non-weightbearing and weightbearing areas of the sole, there appears to be no difference in incidence of ulceration and thickness, and hence prognosis, between the different site [14]. A meta-analysis by Cho et al [12] included studies from all ethnic backgrounds and supports the conclusion that areas of high pressure are associated with higher numbers of melanomas.
However, studies exist which appear to counter the theory. In a US study [14] fewer lesions occurred on the forefoot which is subjected to high pressures. Another showed no difference between acral melanoma incidence on wight bearing areas vs non weightbearing [5] and work studying African tribes found no difference in distribution of AM between those who wore shoes and those who didn’t [5].
Can we conclude trauma causes melanoma in this area?
To date, the studies above which link high pressure sites on the plantar surface to development of AM, are not convincing as location alone cannot imply trauma. Larger cohort and case control studies would be required and other variables such as footwear, foot function and walking surfaces would have to be considered. Lesion distribution itself may be random and therefore a study examining surface area and mapping lesions may give a little more insight into the link between trauma and acral melanoma. For the moment, the role of trauma remains controversial, whilst further examination of the genetics and environmental aspects of AM are required.
This blog was written and submitted by Michelle Reynolds MSc, Podiatrist, Stockport.
References
1. Martín-Carrasco P, Monserrat-García MT, Ortiz-Prieto A, Conejo-Mir J: RF-Acral Melanoma and Repetitive Injury to the Sole of the Foot. Actas Dermosifiliogr 2017, 108:669-670.
2. Sheen YS, Liao YH, Lin MH, Chen JS, Liau JY, Tseng YJ, Lee CH, Chang YL, Chu CY: A clinicopathological analysis of 153 acral melanomas and the relevance of mechanical stress. Sci Rep 2017, 7:5564.
3. Hsu C-K, Lin H-H, Harn HIC, Hughes MW, Tang M-J, Yang C-C: Mechanical forces in skin disorders. J Dermatol Sci 2018, 90:232-240.
4. Dwyer PK, Mackie RM, Watt DC, Aitchison TC: Plantar malignant melanoma in a white Caucasian population. Br J Dermatol 1993, 128:115-120.
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6. Broit N, Johansson PA, Rodgers CB, Walpole ST, Hayward NK, Pritchard AL: Systematic review and meta-analysis of genomic alterations in acral melanoma. Pigment Cell Melanoma Res 2022, 35:369-386.
7. Jung HJ, Kweon SS, Lee JB, Lee SC, Yun SJ: A clinicopathologic analysis of 177 acral melanomas in Koreans: relevance of spreading pattern and physical stress. JAMA Dermatol 2013, 149:1281-1288.
8. Dika E, Veronesi G, Altimari A, Riefolo M, Ravaioli GM, Piraccini BM, Lambertini M, Campione E, Gruppioni E, Fiorentino M, et al: BRAF, KIT, and NRAS Mutations of Acral Melanoma in White Patients. Am J Clin Pathol 2020, 153:664-671.
9. Zhang N, Wang L, Zhu GN, Sun DJ, He H, Luan Q, Liu L, Hao F, Li CY, Gao TW: The association between trauma and melanoma in the Chinese population: a retrospective study. J Eur Acad Dermatol Venereol 2014, 28:597-603.
10. Richard MA, Grob JJ, Avril MF, Delaunay M, Gouvernet J, Wolkenstein P, Souteyrand P, Dreno B, Bonerandi JJ, Dalac S, et al: Delays in diagnosis and melanoma prognosis (I): the role of patients. Int J Cancer 2000, 89:271-279.
11. De Giorgi V, Maida P, Salvati L, Scarfì F, Trane L, Gori A, Silvestri F, Venturi F, Covarelli P: Trauma and foreign bodies may favour the onset of melanoma metastases.Clin Exp Dermatol 2020, n/a.
12. Cho KK, Cust AE, Foo MY, Eslick GD: Melanomas and stress patterns on the foot: a systematic review and meta-analysis. J Am Acad Dermatol 2020.
13. Minagawa A, Omodaka T, Okuyama R: Melanomas and Mechanical Stress Points on the Plantar Surface of the Foot. N Engl J Med 2016, 374:2404-2406.
14. Costello CM, Pittelkow MR, Mangold AR: Acral Melanoma and Mechanical Stress on the Plantar Surface of the Foot. N Engl J Med 2017, 377:395-396.
15. Gong HZ, Zhang S, Zheng HY, Qu T, Li J: The role of mechanical stress in the formation of plantar melanoma: a retrospective analysis of 72 chinese patients with plantar melanomas and a meta-analysis.J Eur Acad Dermatol Venereol 2020, 34:90-96.