In occasional conversations the question is often raised about the skin and cancer. How common is it for metastases to arise on the skin of the foot or leg? This article looks at some literature on this topic to review if the foot is frequently involved.
Metastases represent secondary spread of cancer from a primary tumour to a remote site. Cancerous cells break away from the primary tumour and then are spread through the lymphatics or bloodstream. In some cases, this may be to the skin (a cutaneous metastases [CM]). In most cases the metastases develop after the initial diagnosis has been made - often late in the disease, but occasionally can be the before the primary tumour has been discovered.
Multiple secondaries manifesting on the skin
A study from Ireland [1] undertook a twenty-year review from a regional cancer centre to quantify how often internal malignancies demonstrate secondary cutaneous spread. In twenty-five years only 65 cases of cutaneous metastases were reported. The distribution amongst men and women was equal but the mean age was 63 years. The three most common cancers showing this trait were breast (33%), lung (16.9%) and colon cancers (13.8%). From this data, the presence of metastases were the first manifestation of the disease in just 6.2% of cases. Interestingly, only four CM’s were reported in the lower limb with no specific mention of the foot.
Going back to earlier research from the USA, a 30 year period (1971-2000) at a large academic medical centre reviewed cases of metastases to soft tissue [2]. In this period 118 cases were identified. The average age of these patient was slightly younger (53 years of age). In this cohort, 27% of CM’s were the initial manifestation of malignant disease. In this series, only one CM was reported in the foot in an elderly patient.
Around 5% - 10% of patients with metastases will develop them in the skin. Other work has shown how the skin is the 18th most frequent site for metastasis [3]. From these studies, it would appear that breast and lung cancers are most liable to form CM’s. These tend to occur on skin local to the tumour in these cases most often of the chest. However, malignant melanoma, a skin cancer, may also produce CM’s which can arise in the skin remotely as well but wasn’t covered in these studies as it is a primary skin cancer.
Consequently, it is generally accepted the breast, skin (melanoma), lung, colon, stomach, upper aerodigestive tract (nasal sinuses, larynx, oral cavity), kidney and uterus are the most frequent organs to produce cutaneous metastases [4]. From the available data, it would appear that the foot rarely demonstrates cutaneous metastases.
Despite their rarity, it is important to be mindful of their presentation [4].
· Patients may present with a rapidly developing nodule.
· Lesions can be single or multiple.
· Nodules are often round or oval, firm or rubbery in texture.
· The nodules are usually flesh coloured, although they may be red-purple, brown or blue- black.
Summary
Metastases may arise in the skin as secondaries from internal cancers (particularly breast and lung) and melanoma. In around a quarter of patients, it may be the first sign of malignancy. From available literature, it would appear cutaneous metastases rarely arise on the foot, however podiatrists should always be suspicious of rapidly growing nodules arising on the foot and should always consider referring patients on for a definitive diagnosis.
References
1. Keeling, E., et al., Review of cutaneous metastases from internal malignancies: A 20-year review from a regional cancer treatment centre. Clinical and Experimental Dermatology, 2021. 46(5): p. 923-924.
2. Plaza, J.A., et al., Metastases to soft tissue. Cancer, 2008. 112(1): p. 193-203.
3. Scolyer, R.A., R. Murali, and J.F. Thompson, 17 - Cutaneous Metastases, in Dermatopathology, K.J. Busam, Editor. 2010, W.B. Saunders: Philadelphia. p. 637-650.
4. Cunliffe, T. Cutaneous Metastases. 2013 [cited 2021 March]; Available from: http://www.pcds.org.uk/clinical-guidance/skin-metastases.