10 NCCN Guidelines for Patients ® : Melanoma, 2018 1 Melanoma basics How melanoma spreads Melanoma skin tumors are made of abnormal pigment cells (melanocytes) that have become cancer cells. See Figure 3 . These tumors are usually brown or black in color because the cells still make melanin. Melanoma is more dangerous than most other common skin cancers because it is more likely to spread if it isn’t found early. However, most melanomas—about 84 out of 100—are found early before they have spread and so are likely to be cured with treatment. Melanoma has the potential to spread through the dermis to nearby tissues and other parts of the body. The deeper a melanoma grows into the dermis, the higher the risk of spreading through lymph vessels or blood vessels. This is why finding melanoma as early as possible is so important. Most people can be cured if melanoma is found and treated early. Melanocytes are located at the bottom of the epidermis. These cells make melanin, which spreads to the top of the epidermis and gives skin its color. Melanoma tumors are made of abnormal melanocytes that have become cancer cells. How melanoma spreads Unlike normal cells, cancer cells can spread to other parts of the body. This process is called metastasis. The uncontrolled growth and spread of cancer cells makes cancer dangerous. Cancer cells can replace or deform normal tissue causing organs to stop working. Cancer cells often spread to nearby and distant sites through lymph or blood. Lymph is a clear fluid that gives cells water and food. Lymph leaks out of blood vessels and then flows through tiny tubes called lymph vessels mostly in one direction toward the heart, where lymph re-enters the blood. Lymph also has white blood cells that fight germs. A lymph node is a small group of special disease- fighting cells. Lymph nodes filter lymph and remove germs. Lymph nodes are connected to each other by lymph vessels. Lymph vessels and nodes are found throughout the body. But, the main nodal basins are found in the head and neck, armpits, and groin area. See Figure 4. Once melanoma has grown into the dermis, it can reach the lymph vessels. The melanoma cells can then travel through the lymph vessels to the lymph nodes and other parts of the body. Melanoma can spread anywhere in the body, including the brain. Cancer that spreads from the primary site to a new location is called metastasis. Metastasis to a nearby body part is called a local metastasis. Metastasis to a body part far from the first tumor is called a distant metastasis. Melanoma that has spread into a nearby lymph vessel, but not to lymph nodes, is called an in-transit metastasis. Melanoma that has spread to a small area of skin near the first tumor is called a satellite metastasis.