How the Tumor Grows

How Melanoma Progresses

Primary melanoma is the first place melanoma develops and usually appears in the top layers of the skin. When melanoma is caught at an early stage, chances are good that the entire tumor can be removed surgically, before it spreads to other parts of the body.

Most primary melanomas will grow and spread horizontally along the epidermis, or the top layer of skin, before they begin to penetrate deeper into the layers of the skin and develop an ulceration (where the top layer of the skin over the melanoma is not fully covering it).

In early stages, melanoma spreads laterally across the top layer of the skin

As it grows deeper into the skin, it may become ulcerated

When the melanoma grows deeper, it reaches the blood vessels and lymph nodes of the dermis

When the melanoma grows deeper into the skin, it reaches the lymph nodes and blood vessels of the dermis, which may allow cancerous cells access to your entire system.

  • When cancer cells break away from the primary tumor, they enter lymph vessels. They may spread along these lymph vessels. Cancer that grows from melanoma cells that are “en route” to a regional lymph node are called “in-transit” metastases.
  • When cancer cells invade blood vessels, they may be able to travel through the bloodstream to distant parts of the body. When this happens, it is called metastatic melanoma. The most common areas where melanoma can metastasize are the lungs, the abdominal organs, the brain, and bone.

Probability of Developing Melanoma of the Skin

GenderBirth to 49 (%)50 to 59 (%)60 to 69 (%)70 and older (%)


(1 in 297)

(1 in 238)

(1 in 127)

(1 in 45)


(1 in 206)

(1 in 321)

(1 in 242)

(1 in 107)

Note: Based on data from 2010-2012.

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