Melanoma is a skin cancer that develops in pigment-producing cells called melanocytes. A melanoma’s growth behavior helps classify its potential risk and determines the approach to treatment.
The Radial Growth Phase Explained
Melanoma develops in two distinct growth phases: radial and vertical. The radial growth phase is the initial stage, where cancer cells spread horizontally across the epidermis, the skin’s outermost layer. During this period, the lesion expands outwards as a flat or slightly raised patch, and the malignant cells have not yet penetrated deeper skin layers.
In contrast, the vertical growth phase occurs when the tumor grows downwards into the dermis. This invasion allows cancer cells to reach blood and lymph vessels, increasing the risk of metastasis, or spreading to other parts of the body. The term “radial melanoma” describes any melanoma currently in the initial, horizontal growth stage.
This distinction matters because a melanoma confined to the radial growth phase has a very low potential to spread. The transition to vertical growth signals more aggressive tumor behavior and a more serious prognosis.
Visual Identification and Symptoms
Recognizing a melanoma in its radial growth phase relies on careful skin observation. The “ABCDE” rule is a guide for identifying suspicious moles or spots.
- Asymmetry: One half of the mole does not match the other.
- Border: The edges are irregular, scalloped, or poorly defined.
- Color: There are varied shades of brown, tan, and black, or patches of red, white, or blue.
- Diameter: The mole is often larger than 6 millimeters, though they can be smaller.
- Evolving: The mole changes in size, shape, color, or elevation, or develops new symptoms like bleeding or itching.
A spot that looks different from others on your body, known as the “ugly duckling sign,” is another warning signal. In its radial phase, a melanoma appears as a flat or slightly raised patch with a smooth or scaly surface. While helpful, not all melanomas display every feature, and many cause no discomfort.
Diagnosis and Prognosis
Diagnosing a suspected melanoma begins with a visual examination by a dermatologist, who may use a handheld magnifying tool called a dermatoscope. This device offers a detailed view of the mole’s structure and pigment, helping the doctor decide if a biopsy is necessary.
If a lesion is suspicious, a skin biopsy provides a definitive diagnosis. A tissue sample is removed and sent to a pathologist, who analyzes the cells to determine if melanoma is present and identify its characteristics.
The pathology report includes the tumor’s “Breslow depth,” which measures how deeply it has invaded the skin. For melanomas in the radial growth phase, the Breslow depth is very thin, often under 1 millimeter. Since the cancer has not penetrated deeply, the prognosis is excellent, with a 5-year survival rate over 99% for localized melanoma.
Medical Treatments
The standard treatment for a radial phase melanoma is a wide local excision. This surgical procedure involves removing the tumor along with a surrounding margin of healthy skin. A pathologist then examines the excised tissue to confirm the margins are clear of cancer cells.
For melanomas on the face or other cosmetically sensitive areas, Mohs surgery may be an option. This technique involves removing the tumor one thin layer at a time. Each layer is immediately examined under a microscope, and the process continues until no cancer cells are detected, which preserves healthy tissue.
For melanomas treated during the radial growth phase, surgical excision is curative, and no further treatment is necessary. Follow-up care focuses on regular skin examinations to monitor for new or changing lesions.