Plantar melanoma is a form of skin cancer that originates on the soles of the feet, the toes, or beneath the toenails. This type of melanoma can be aggressive. Its concealed location often leads to delayed detection, making early identification important.
What is Plantar Melanoma?
Plantar melanoma is a specific type of skin cancer known as acral lentiginous melanoma (ALM), which commonly develops on the soles, heels, toes, or within the nail beds. Although relatively uncommon, it is frequently diagnosed at a more advanced stage due to its hidden location and potential for delayed discovery. Unlike many other melanomas, plantar melanoma is not primarily associated with sun exposure.
This form of melanoma is the most common type of melanoma found in individuals with darker skin tones, including those of Asian descent. Its occurrence is also linked to older age, a family history of melanoma, and sometimes previous trauma to the affected area. A significant challenge with plantar melanoma is its frequent misdiagnosis, often mistaken for benign conditions such as warts, corns, fungal infections, bruises, or non-healing ulcers. This misidentification can lead to a median delay in diagnosis of about nine months, potentially worsening the prognosis.
Recognizing the Signs
Healthcare professionals often use the “ABCDE” rule, adapted for acral melanoma, to help detect suspicious lesions.
“A” stands for Asymmetry, meaning one half of the spot does not match the other.
“B” refers to Border irregularity, where the edges of the lesion may appear ragged, blurred, or notched.
“C” denotes Color variability, indicating that the spot may contain multiple shades of black, brown, tan, or even areas of white, red, pink, or blue.
“D” represents Diameter, with melanomas often being larger than 6 millimeters, roughly the size of a pencil eraser, though some can be smaller. “E” signifies Evolving, highlighting any changes in the mole’s size, shape, color, or elevation over time, or new symptoms like itching or bleeding. Additionally, some guidelines suggest considering “F” for flat or “G” for growing as further indicators. A new, darkened streak in a toenail not caused by trauma, especially if it grows sideways or faster than the nail, can also be a sign.
Regular self-examinations of the feet, including hard-to-see areas like between the toes and under toenails, are encouraged. Any new, changing, or suspicious spots on the feet warrant immediate consultation with a healthcare professional.
Diagnosis and Treatment
Diagnosis of plantar melanoma begins with a clinical examination by a healthcare professional, often using a dermatoscope to get a magnified view of the skin lesion. The definitive diagnostic step is a biopsy, where a tissue sample is removed for laboratory testing. Common biopsy techniques include excisional biopsy, which removes the entire growth with a small margin of surrounding healthy tissue, or punch biopsy, which uses a circular blade to take a deeper sample.
Once melanoma is confirmed, staging determines how deeply the cancer has spread and its characteristics under a microscope. Tumor thickness is a factor in predicting outcomes. Staging also considers whether the melanoma has spread to nearby lymph nodes or distant organs. For melanomas deeper than 0.8 mm or those with ulceration, a sentinel lymph node biopsy may be performed to check for spread to the nearest lymph nodes.
The primary treatment for plantar melanoma is surgical removal of the tumor, along with a margin of healthy tissue. The recommended margin size depends on the melanoma’s thickness; for example, a 1 cm margin is often used for melanomas less than 1 mm thick, while a 2 cm margin is recommended for thicker lesions. For more advanced or metastatic cases, additional treatment modalities may be considered, including radiation therapy, chemotherapy, targeted therapy, and immunotherapy.
Living with Plantar Melanoma and Outlook
The prognosis for plantar melanoma is closely tied to the stage at which it is diagnosed and treated. Early detection and prompt intervention improve outcomes. While some reports suggest that melanomas on the palms and soles might have a poorer prognosis compared to similar melanomas on other body sites, other studies indicate that tumor thickness is the most influential prognostic factor.
After initial treatment, ongoing follow-up appointments are necessary to monitor for any signs of recurrence or the development of new lesions. These follow-up visits involve regular skin examinations and may include imaging tests or blood work, depending on the stage of the initial diagnosis. Patients are also encouraged to continue performing regular self-examinations of their feet. Beyond medical care, emotional and psychological support can be beneficial for patients and their families.