What are the common pedal skin tumours?
Skin tumours are a source of concern for the patient and podiatrist alike, and suspicious lesions should be dutifully referred for urgent assessment where malignancy is suspected. From an academic perspective, looking through the literature, a bewildering array of rare and not-so-rare tumours on the feet have been reported over the years but little data exists on their incidence. In the journal "Clinical and Experimental Dermatology", a large retrospective data set (1) reviewing 802 acral tumours was published which begins to give some insight into the profile of skin tumours we may encounter on the foot.
Amelanotic Melanoma – Cantwell & Van Damm (2019) (2)
Reproduced under Creative Commons Licence
The study was conducted at two centres in Korea where they collated the data from a 10-year period (2009-2019) of all skin tumours with a confirmed diagnosis from a biopsy arising in acral areas. The term acral can have different meanings but for the purpose of this study, it included the palms, soles and nails of all digits but excluded the dorsum of the foot and hand.
For analysis, the researchers classified lesions into six distinct locations – the palms, the volar surfaces of the fingers, the fingernail and the soles, the volar surface of the toes and the toenail. In total, over 10 years, 802 lesions were diagnosed in patients (58.5% women, 41.5% men). The average age at diagnosis was 43.8 years old and the mean duration of the lesions were nearly 69 months (5 years and 9 months).
Focusing on foot lesions of the 802 lesions, 515 (64.3%) occurred on the foot. This was broken down as follows:
408 on the sole (79.2%)
58 on the toes (11.3%)
49 in the toenail (9.5%)
Of the lesions arising on the foot, 304 were benign (59%) and 211 (41%) were malignant. The most common benign lesions were moles (200) [66%], followed by epidermal cysts (32) [11%], fibromas (18) [6%], pyogenic granuloma (13) [4%]. The malignant lesions were as follows:
173 [83%} melanoma
17 [8%) squamous cell carcinoma
6 [3%] verrucous carcinoma
1 [>1%] basal cell carcinoma
1 [>1%] metastatic carcinoma
The majority of nail lesions were melanoma with only 1 case of squamous cell carcinoma (SCC) and one verrucous carcinoma (VC).
This research gives an insight into profile of skin tumours on the foot (soles, nails and volar surfaces of the toes) but does not include the dorsum of the foot. Moles were the most reported benign lesion on the foot in this study, making up 66% of all benign lesions and along with epidermal cysts, fibroma and pyogenic granulomas together accounting for nearly 89% of benign lesions. Epidermoid (or epidermal) cysts are not a common clinical diagnosis within podiatry but are usually only discovered through pathology reports following excision of plantar lesions. Typically, they are a tumour of the sebaceous glands but as there are none on the sole of the foot, it probably represents a foreign body reaction in the foot or traumatic sequestration of epidermis into the dermis leading to the development of a swelling or tumour (3).
From this work, it would appear the malignant melanoma (MM) is the most common malignant skin tumour arising on the foot by some margin. This has been reported in another study and confirms this earlier observation (4). The vast majority of MM (81%) arising on the soles with just 8% in the nail unit and the remainder on the volar surface of the toes. MM in these typically acral locations are most often the acral lentiginous melanoma (ALM) sub-type of the disease. ALM are not strongly related to sun exposure (unlike other types of melanomas) however it is not clear what their actual aetiology is.
Squamous cell carcinoma is a less common tumour on the foot, occasionally found on the soles of older adults. Many of these tumours may mimic ulcers and are frequently delayed in their diagnosis (5-7). As they are predominantly due to excessive UV exposure, they are rare on the sole of the feet. However, they can arise in areas of chronic inflammation and sites of trauma which may explain their occasional appearance in this area. Verrucous carcinoma are highly differentiated squamous cell carcinoma variants occurring mostly on the soles of the feet in older adults (8). They and are often slow growing lesions which may resemble verrucae.
It is important to state that this research was conducted at a tertiary hospital centre. The rate of malignant to benign lesions was probably elevated compared to primary care as it only included patients who had had a biopsy. Many benign lesions would be diagnosed without a biopsy in the community. Moreover, tertiary care centres are often predominantly focussed on skin cancers and pigmented lesions, and this may be reflected in the findings of this work
1. Park HK, Choi YD, Yun SJ. Clinical characteristics and differences of 802 acral tumours, categorized by anatomical sites. Clin Exp Dermatol. 2022;47(2):312-8.
2. Cantwell P, Van Dam H. Acral Amelanotic Melanoma Mimicking a Non-Healing Arterial Ulcer. Case reports in dermatology. 2019;11(1):77-81.
3. Ramakrishnaiah SB, Rajput SS, Gopinathan NS. Epidermoid Cyst of the Sole - A Case Report. J Clin Diagn Res. 2016;10(11):Pd06-pd7.
4. Barnes B, Seigler H, Saxby T, Kocher M, Harrelson J. Melanoma of the foot. J Bone Joint Surg Am. 1994;76:892-8.
5. MacIntyre K, Goodfellow T, Bristow I. Case Report: Squamous cell carcinoma or diabetic foot ulcer? Diabetic Foot Journal. 2008;11(1):22-4.
6. Mandal PK, Bhattacharyya NK, Mookerjee SK, Chaudhuri B. Primary squamous cell carcinoma with mucormycosis in a diabetic foot ulcer. J Indian Med Assoc. 2013;111(2):125-6.
7. Chiao HY, Chang SC, Wang CH, Tzeng YS, Chen SG. Squamous cell carcinoma arising in a diabetic foot ulcer. Diabetes Res Clin Pract. 2014;104(2):e54-6.
8. Gordon DK, Ponder EN, Berrey BH, Kubik MJ, Sindone J. Verrucous carcinoma of the foot, not your typical plantar wart: A case study. The Foot. 2014;24(2):94-8.