8 NCCN Guidelines for Patients ® : Melanoma, 2018 1 Melanoma basics Layers of the skin | About melanoma You’ve learned that you have or may have melanoma. Part 1 explains some basics about this cancer that may help you learn about it and start to cope. These basics may also help you start planning for treatment. Layers of the skin The skin is the largest organ of the body. The skin has two layers. The outer layer, which can be seen, is called the epidermis. The second layer, under the epidermis, is called the dermis. Under the dermis is the subcutaneous tissue. See Figure 1 . Epidermis The main job of the epidermis is to protect the body and help control body temperature. It is made up of four types of cells, including pigment cells called melanocytes. Melanocytes are located at the bottom of the epidermis. These cells make a pigment called melanin, which moves to the top of the epidermis and gives skin its color. People with darker skin have the same number of melanocytes as people with lighter skin. The darkness of skin is based on how much melanin is made by the melanocytes. Higher levels of melanin cause the skin to be darker. Dermis The dermis is much thicker than the epidermis. It contains hair roots, blood vessels, lymph vessels, glands, and nerve endings. Blood and lymph vessels in the dermis bring nutrients to the dermis and epidermis. Glands make fluids or chemicals the body needs. Connective tissue holds all these structures in place and allows the skin to stretch. Under the dermis is the subcutaneous tissue. Subcutaneous means “below the skin.” It is mostly made of fat and connective tissue. It is not part of the skin but connects the skin to muscles and bones. It also saves body heat, stores energy, and absorbs shock to protect the body from injury. About melanoma Cells are the building blocks that form tissue in the body. Genes are the instructions in cells for making new cells and controlling how cells behave. Abnormal changes (mutations) in genes can turn normal cells into cancer cells. Normal cells divide to make new cells. New cells are made as the body needs them to replace injured or dying cells. Normal cells stay in one place and do not spread to other parts of the body. When normal cells grow old or get damaged, they die. Cancer cells do not do this. Cancer cells don’t stay in place as they should. Cancer cells make new cells that aren’t needed and don’t die quickly when old or damaged. Over time, cancer cells grow and divide enough to form a malignant tumor. See Figure 2 . The first tumor formed by the overgrowth of cancer cells is called the primary tumor. Researchers are still trying to learn what causes genes to mutate and cause cancer.