How Melanoma Develops

From Cells to Tumors

To keep the body healthy, normal skin cells continually grow, divide, mature, and, after a set period of time, die and are sloughed off. When we are young, the cell growth happens quickly to keep up with the building and developing of the body. As we age, the new cells that are produced are created to replace worn-out or dying cells. Sometimes though, cells keep dividing when new cells are not needed, or fail to heed signals to stop growing and die. This mass of cells forms a growth or tumor.

Cancer cells develop because of damage to genes in a cell’s DNA, the part of a cell that carries genetic information and passes it from one generation to the next. This damage is called a mutation, and a mutation can lead to inappropriate growth of the cells. Mutations can cause a cell to acquire the ability to move and survive in locations in the body where it was not supposed to be. Because a cell copies its own DNA before it divides to make new cells, any mutations in the original cell will be passed along to the cells that follow.

  • DNA (deoxyribonucleic acid) is a very large molecule that acts like a recipe book for a cell.
  • The cell uses the information stored within the DNA molecule to create all the proteins that a cell needs to survive and perform its vital functions.
  • Each section of the DNA that codes for a protein is called a gene. In this analogy, each gene is a unique recipe. A mutation is a change in the DNA code and is like changing a word in a recipe.
  • Some of the proteins made from the DNA act as controls that promote or inhibit a cell’s ability to replicate itself. If the genes, or recipes for the proteins that control cell growth and division, are changed, they do not work as they should.

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

Birth to 39 (%) 40 to 59 (%) 60 to 69 (%) 70 and older (%)


0.15 %
(1 in 656)

(1 in 164)

0.66 %
(1 in 151)

(1 in 64)


0.26 %
(1 in 389)

(1 in 200)

(1 in 297)

(1 in 140)

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