These cells are located in the uppermost layer of the skin. They are responsible for producing melanin, a dark pigment that helps screen the body against the harmful effects of ultraviolet light.
Contents of this article:
- Foot melanoma is a rare but serious form of skin cancer.
- It constitutes 1 percent of skin cancers but more cancer deaths than any other type of skin cancer.
- Between 3 and 15 percent of melanomas occur on the foot.
- The first symptom in most cases of foot melanoma is a changing or unusual mole.
- Check symptoms with the acronym CUBED. Is it Colored, Uncertain, Bleeding, Enlarged, or is there Delay in the healing of lesions?
What is foot melanoma?
Foot melanoma can appear on the sole or under a nail, and is often not detected until an advanced stage of the cancer.
Foot melanoma is a type of cancer that affects the skin cells in the foot. In cancer, cells grow too fast and do not die off as healthy cells do.
Melanoma is not the only type of skin cancer. It accounts for only 1 percent of skin cancers, yet it accounts for the highest number of deaths from skin cancer. Between 3 and 15 percent of melanomas occur on the foot.
Various types of melanoma can appear on the foot and under the toenails.
Acral lentiginous melanoma (ALM): Around half of the cases of melanoma that appear on the feet are of this type. ALM grows equally all skin types, but it appears more often on darker skin. In the early stages, it can be hard to see, presenting as a light patch of discoloration of the skin.
Nodular melanoma (NM): This is a pigmented, or colored, lesion that appears to have small nodules when viewed with the naked eye. NM is the type most likely to affect older patients.
Superficial spreading melanoma (SSM): SSM is the most common melanoma. It grows outwards across the skin, rather than inwards towards the body's organs and systems. It most often occurs on the upper surface of the foot.
Amelanotic melanoma: These have no color and may be flesh-like in appearance. As a result, they are often misdiagnosed as more benign conditions, such as ulcers.
Different types of melanomas can have similar characteristics. The exact type may only be confirmed under a microscope or through laboratory testing.
Signs and symptoms
The first sign of melanoma is often a change in the size, shape, color, or texture of an existing mole.
Most people have moles, and most are harmless, but identifying changes is crucial to catching melanoma early. This applies to any unusual sores, lumps, blemishes, or markings on the skin surface.
Most melanomas have a black or blue-black area. Melanoma may appear as a new or unusual mole.
Two acronyms can help you remember what to look out for.
The acronym ABCDE provides a handy way to remember the signs of melanoma generally.
- Asymmetry: One-half of the lesion is not identical to the other.
- Border: The lesion has an irregular, ragged or indistinct border.
- Color: The lesion is more than one color.
- Diameter: The lesion has a diameter greater than 6 mm.
- Evolution: The lesion changes in size, shape or color.
If you have any of these warning signs, have your skin checked by a doctor.
Foot melanoma usually appears on the sole or under a toenail, but can appear anywhere on the foot or ankle. A new acronym, specifically for foot melanoma, is CUBED:
- Colored: A lesion has a color different to normal skin.
- Uncertain: A lesion does not have a definite diagnosis.
- Bleeding: A lesion on the foot or under the nail bleeds or oozes fluid.
- Enlargement: A lesion or ulcer that grows or worsens despite therapy.
- Delay: Any lesion that takes longer than 2 months to heal.
Other warning signs for foot melanoma include:
- a sore that does not heal
- pigment spreading from the border of a lesion to surrounding skin
- redness or new swelling beyond the border of a lesion
- change in sensation such as itchiness, tenderness, or pain
- change in the surface of a mole including scaliness, oozing, bleeding, or the appearance of a bump or nodule
If two of the above are present, the doctor will normally refer the patient to a specialist for further assessment.
Causes and risk factors
Ultraviolet (UV) light, whether from the sun or an artificial source such as a tanning bed, is a major cause of skin cancer. UV rays damage the DNA in skin cells, which affects how they grow and divide.
Irregular and intense exposure to sunlight significantly increases the risk of melanoma.
However, the role of UV light in melanomas of non-exposed areas, such as the sole, is unclear.
Melanoma on areas of skin rarely exposed to the sun may result from genetic changes that are different from those in areas exposed to sunlight.
Other known risk factors for melanoma skin cancer development include:
- existing moles
- pale skin, freckles, and light hair
- family or personal history of melanoma
- xeroderma pigmentosum: This is a rare genetic disorder that leads to an impaired ability of the skin cells to repair damaged DNA, and can increase the risk of melanoma in younger people.
Cancers of the foot and ankle can be difficult to identify. If a person approaches a doctor with concerns about skin changes on the foot, the doctor will examine the area and ask about any family history of skin cancer.
They will assess
- the approximate date of the lesion's appearance
- any changes in size and appearance
- additional signs or symptoms such as pain, itching, or bleeding
- any other suspicious moles
- the lymph nodes near the abnormal area, to rule out any spread, or metastasis
If the doctor suspects melanoma, they will refer the patient to a dermatologist. The dermatologist will use a dermatoscope to see spots on the skin more clearly.
Biopsy types and uses
A biopsy involves taking a skin sample for examination under a microscope. The type of biopsy depends on the affected area and size of the lesion.
- Skin biopsy: A skin sample is taken under local anesthetic.
- Shave biopsy: Samples are taken from the top two layers of skin. A shave biopsy cannot assess the depth of a lesion beneath the skin.
- Punch biopsy: A "cookie-cutter" tool retrieves a sample of all layers of skin, including the subcutaneous layer underneath.
- Incisional or excisional biopsy: Part or all of a mole is removed and examined. This is often preferred for suspected melanomas.
In some cases, a fine needle aspiration (FNA) or surgical biopsy may be used to check nearby lymph nodes for melanoma. This can show if the cancer has spread.
In some cases, a melanoma lesion can form on the skin and then disappear. However, the cells can travel through the body, and cause cancer to develop elsewhere.
A biopsy can show whether the cells are cancerous, and which type of cancer is present. It can also show how thick a tumor is, and how fast it is progressing.
If the cancer is limited to one site, it is classified as Stage I cancer. By stage 4, it has spread to distant organs and systems.
Diagnosing cancer at Stage I greatly increases the chance of successful treatment.
Imaging tests may be used, such as an x-ray, CT, or MRI scan. These can help assess whether the cancer has spread, how well treatment is working, and whether cancer has returned after treatment.
Genetic testing may reveal other factors that can affect treatment. Cells may also be tested for any genetic qualities that may impact the course of treatment. Cells with the BRAF gene, for example, may respond more effectively to certain treatments.
Treatment and prevention
Surgery is the main treatment for melanoma that is diagnosed early.
In the early stages, melanoma can be surgically removed without significant functional or aesthetic impairment, but recurrences may need more radical intervention.
If the melanoma does not go away with treatment, regular immunotherapy, targeted therapy, or other treatments may help keep the cancer in check.
The risk of melanoma is higher in people who have had more exposure to UV light.
The sole is rarely exposed to the sun, but the following precautions may help reduce the risk of foot melanoma.
- Wearing water shoes or shoes and socks instead of being barefoot or wearing flip-flops.
- Using adequate sunscreen in areas unprotected by clothing or shoes, and apply sunscreen on the soles as well as the tops of feet.
- Inspecting all areas of the feet daily, including the soles, underneath the toenails, and between the toes.
- Removing nail polish occasionally, if you wear it, to inspect the skin underneath the toenails. Avoid using UV drying lamps during a pedicure.
- Avoiding UV radiation between 10 and 4 pm. Sun exposure is especially damaging to children and adolescents. Infants should be kept out of intense sunlight.
Any time you are in the sun, it is a good idea to protect yourself from UV rays by wearing sunglasses that block all UV rays and a wide-brimmed hat.
It is important to check the feet, including the nails and the soles, for any skin changes, and to seek medical attention if any unusual features appear.