Foot melanoma, a type of acral melanoma, is a variant of skin cancer that develops on the feet. It can appear anywhere on the foot, including on the sole or under a nail. It starts in a type of skin cell called a melanocyte.
These cells are present 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 (UV) light.
Foot melanoma is often treatable in the early stages. However, people will usually receive a diagnosis during the later stages, as the symptoms may not be easily noticeable.
If foot melanoma spreads, or metastasizes, it can be life threatening. Foot melanoma most often initially spreads to the lymph nodes.
In this article, we explain the different types of foot melanoma, how to recognize the early symptoms, and ways to prevent and treat them.
Cancer develops when cells grow uncontrollably and do not die at the usual point in their life cycle.
Foot melanoma is a type of cancer that affects the pigment-producing skin cells in the foot. Around 3–15% of melanomas occur on the foot.
Melanoma can spread. However, the outlook tends to be better when a person receives early diagnosis and treatment.
Various types of melanoma can appear on the foot and under the toenails.
Different types of melanoma can have similar characteristics. A doctor can only confirm the exact type by sending a tissue sample for examination under a microscope or laboratory testing.
The different types of foot melanoma include:
Acral lentiginous melanoma
Around half of all cases of melanoma that appear on the feet are acral lentiginous melanoma. This type of melanoma develops equally in all skin colors but represents a greater proportion of melanomas in darker-skinned people.
In the early stages, it can be hard to identify. It presents as a darker patch of discoloration of the skin. It can also occur in the nail and appear as a wide, dark streak on the nail. However, it is important to note that not all dark streaks on the nail indicate melanoma.
This is typically a very dark blue-black papule. Nodular melanoma is the type most likely to develop in older adults.
Superficial spreading melanoma
Superficial spreading melanoma is the most common type of melanoma. It grows outward across the skin, rather than inward toward the body's organs and systems.
When on the foot, it most often occurs on the upper surface.
These have no color and may resemble a person's flesh. As a result of this, when they occur on the foot, doctors may misdiagnose them as less aggressive conditions.
The first sign of melanoma is often a change in the size, shape, color, or texture of an existing mole. However, it may also present as a new mole.
Many people have moles, and most moles are harmless.
However, identifying changes in moles is crucial to catching melanoma early. This applies to any unusual sores, lumps, blemishes, or markings on the surface of the skin. Most melanomas have a black or blue-black area.
Two acronyms can help a person remember the signs of a changing mole.
The acronym ABCDEis a handy way to remember the signs of melanoma generally:
- Asymmetry: 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 millimeters.
- Evolution: The lesion gradually changes in size, shape, or color.
If a person notices any of these symptoms, it is important to seek consultation with a doctor.
Foot melanoma usually appears on the sole or under a toenail but can appear anywhere on the foot or ankle. One set of 2010 guidelines in the Journal of Foot and Ankle Research suggests an acronym specifically for foot melanoma: CUBED.
This reads as follows:
- Colored: A lesion has a color different to the rest of the skin.
- Uncertain: A lesion does not have a definite diagnosis.
- Bleeding: A lesion on the foot or under the nail bleeds or leaks fluid.
- Enlargement: A lesion or ulcer grows or gets worse despite treatment.
- Delay: A lesion 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
- changes in sensation, such as itchiness, tenderness, or pain
- changes in the surface of a mole, including scaling, oozing, bleeding, or the appearance of a bump or nodule
If two of the above symptoms are present, a doctor will normally refer a person to a skin cancer specialist for further assessment.
UV light is a major cause of skin cancer, whether from the sun or an artificial source, such as a tanning bed. UV rays damage the DNA in skin cells. This affects how they grow and divide.
Regular and intense exposure to sunlight significantly increases the risk of melanoma.
However, the role of UV light in the development of melanomas on nonexposed areas, such as the sole of the foot, remains unclear.
Melanoma on rarely exposed areas of skin may result from genetic changes that are different from those in areas that receive regular exposure to sunlight.
Other risk factors for melanoma include:
- existing moles
- pale skin, freckles, and light hair
- a family or personal history of melanoma
- xeroderma pigmentosum, 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
Melanomas rarely occur before puberty and are more likely to affect older adults.
Before 50 years of age, the risk of melanoma is higher among women. After this age, however, the risk becomes higher in men.
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 the person about any family history of skin cancer.
They will also assess:
- the approximate date of the lesion's development
- 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 make sure that the cancer has not spread
If the doctor suspects melanoma, they will refer the individual to a dermatologist. This is a doctor who specializes in treating skin conditions and cancers.
The dermatologist will use a dermatoscope to see spots on the skin more clearly, and they will perform a biopsy on the lesion if it appears suspicious.
Biopsy types and uses
In a biopsy, a health professional will collect a skin sample and send it for examination under a microscope. The type of biopsy depends on the affected area and size of the lesion.
- Skin biopsy: A health professional will collect a skin sample under local anesthetic. "Skin biopsy" is a general term that refers to any form of skin biopsy, including a shave or punch biopsy.
- Shave biopsy: A health professional will use a blade to remove the lesion of interest. It heals with a scar and does not require sutures.
- Punch biopsy: Using a "cookie-cutter" tool, a health professional will take a sample of all skin layers, including the subcutaneous layer under the skin. They will usually place a suture to close up the biopsy site, which they will remove 1–2 weeks later.
- Incisional or excisional biopsy: A health professional will remove part or all of a mole and send it for examination. This is often the preferred method for assessing suspected melanomas.
In some cases, a doctor may ask for further studies, such as surgical evaluation, to evaluate for lymph node involvement. This can also evaluate for the spread of the cancer.
In some cases, a melanoma lesion can form on the skin and then disappear. However, the cells may travel through the body and cause cancer to develop elsewhere.
A biopsy can identify whether the cells are cancerous and which type of cancer, if any, is present. It can also measure the thickness of a tumor.
If melanoma has not spread from its original site, it is a stage 1 cancer. By stage 4, it has spread to distant organs and systems. Melanoma can also be stage 0, meaning that it shows signs of being cancerous but has not yet invaded through the skin.
Diagnosing cancer at stage 1 greatly increases the chance of successful treatment.
A dermatologist or oncologist might request imaging tests, such as a CT or MRI scan. These can help assess whether the cancer has spread, how well treatment is working, and whether or not cancer has returned after treatment.
Genetic testing, meanwhile, may reveal other factors that can improve the outlook of treatment. Cells may also undergo genetic testing, as the genetic qualities of a cancer may impact the course of treatment.
For example, cells with the BRAF gene might respond more effectively to certain treatments.
Surgery is the main treatment option for melanoma that a dermatologist has diagnosed early.
In the early stages, a surgeon can remove the melanoma without significantly affecting a person's daily function or the appearance of their skin. However, if the melanoma returns, a person may need more radical intervention.
If the melanoma does not resolve 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 longer, more regular exposure to UV light.
The sole of the foot rarely has sun exposure, but taking the following precautions may help reduce the risk of foot melanoma:
- wearing water shoes or shoes and socks instead of going barefoot or wearing flip-flops
- using adequate sunscreen in areas that clothing and shoes do not protect
- inspecting all areas of the feet daily, including the soles, underneath the toenails, and between the toes
- removing nail polish occasionally to inspect the skin underneath the toenails
- not using UV drying lamps during a pedicure
- avoiding UV radiation from the sun between 10 a.m. and 4 p.m., especially for younger children and infants, who are particularly susceptible to the effects of UV radiation
People can also protect themselves from the sun's UV rays by wearing sunglasses that block all UV rays and a wide brimmed hat. Sunscreen is available to purchase online.
That said, experts do not believe that acral melanoma — which affects the soles of the feet — is related to sun exposure. Therefore, it is not possible to prevent this type of melanoma by protecting oneself from UV rays from the sun.
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.