Understanding How Melanoma Spreads Beneath the Skin

You’ve likely heard that melanoma is the most serious type of skin cancer, but what makes it so dangerous is its ability to grow and spread. Understanding how this process works beneath the surface is key to recognizing its seriousness and the critical importance of early detection. This guide breaks down the patterns of melanoma growth, according to dermatological science.

The Two Primary Growth Phases of Melanoma

When a melanoma first develops, it typically goes through two distinct phases of growth. How it behaves during these phases determines its potential to become life-threatening. Dermatologists look closely at these patterns to understand the stage and severity of the cancer.

1. The Radial Growth Phase (Spreading Outward)

The first phase is called the radial growth phase. During this stage, the cancerous cells grow horizontally within the epidermis, which is the very top layer of your skin.

Think of it like a stain spreading slowly across the surface of a piece of paper. The mole or lesion might get wider, change shape, or develop irregular borders, but it remains thin and confined to the skin’s surface.

This is the most crucial time for detection. When melanoma is identified and treated during the radial growth phase, it is almost always curable because the cancer cells have not yet reached the deeper structures that would allow them to travel to other parts of the body. This is why regular skin checks, either by yourself or a dermatologist, are so important.

2. The Vertical Growth Phase (Growing Downward)

The second and more dangerous phase is the vertical growth phase. This is the “beneath the skin” spread that the ad refers to. In this stage, the cancer cells stop spreading outward and begin to grow downward, invading the deeper layers of the skin, such as the dermis.

Once the melanoma cells reach the dermis, they gain access to two critical transportation networks in your body:

• Blood Vessels: Tiny blood vessels in the dermis can pick up cancer cells, allowing them to travel through your bloodstream to distant organs.
• Lymphatic System: This network of vessels, which helps your body fight infection, can also carry melanoma cells to nearby lymph nodes and then to other parts of the body.

The transition from the radial to the vertical growth phase is the single most important event in the progression of melanoma. It marks the point where the cancer gains the ability to metastasize, or spread to other organs.

How Dermatologists Measure and Stage the Spread

To determine how far a melanoma has spread, dermatologists and pathologists use very specific measurements after a biopsy is performed. These measurements are critical for determining the prognosis and the best course of treatment.

Breslow’s Depth

The most important factor in predicting the outcome of a melanoma is its thickness, measured in millimeters. This is known as the Breslow’s depth. It measures the distance from the top layer of the epidermis down to the deepest point of the tumor.

• Thin Melanomas (less than 1.0 mm): These have a very high cure rate, often with surgery alone. They are typically still in the radial growth phase or have only just begun the vertical phase.
• Thick Melanomas (greater than 1.0 mm): As the Breslow’s depth increases, so does the risk that the melanoma has spread to the lymph nodes or other parts of the body. These require more aggressive treatment and follow-up.

Ulceration

Another key factor dermatologists look for is ulceration. This refers to whether the skin over the top of the melanoma has broken down. An ulcerated melanoma is considered more aggressive and has a higher risk of spreading, regardless of its thickness.

Metastasis: When Melanoma Spreads Beyond the Skin

If melanoma is not caught before or during the early vertical growth phase, it can metastasize. This means it has traveled from the original site on the skin to other parts of the body.

The process usually follows a pattern:

1. Local Spread: The cancer cells first travel to the nearby lymph nodes. Your doctor may recommend a sentinel lymph node biopsy, a procedure to check the first few lymph nodes where cancer is likely to spread.
2. Distant Spread: If the cells get past the lymph nodes, they can travel through the bloodstream or lymphatic system to almost any organ in the body. The most common sites for melanoma metastasis are the lungs, liver, brain, and bones.

Once melanoma has spread to distant organs, it is classified as Stage IV and is much more difficult to treat. However, recent advances in treatments like immunotherapy and targeted therapy have significantly improved outcomes for patients with advanced melanoma.

The key takeaway from dermatologists is clear: the danger of melanoma lies in its depth. By understanding its growth patterns, we can appreciate why early detection is not just important, it is the single most effective tool we have to fight this disease.

Frequently Asked Questions

What are the warning signs of the vertical growth phase? A mole that becomes raised, firm, or starts to grow like a bump is a classic warning sign of vertical growth. Other signs can include itching, bleeding, or crusting on a pre-existing or new mole. Any of these changes warrant an immediate visit to a dermatologist.

How quickly does melanoma spread? The speed of growth and spread can vary greatly from person to person and depends on the specific type of melanoma. Some types, like nodular melanoma, are aggressive and begin the vertical growth phase almost immediately. Others may stay in the radial phase for years. Because this is unpredictable, any changing spot should be evaluated promptly.

Can melanoma be cured if it starts to spread? Yes. If it has only spread to nearby lymph nodes (Stage III), treatments like surgery and adjuvant therapy (immunotherapy or targeted therapy) can still be curative. Even for Stage IV melanoma, modern treatments can lead to long-term remission in some patients. However, the prognosis is always best when the cancer is caught before it spreads at all.