Melanoma is a form of skin cancer, and stage 3 melanoma is the fourth stage of development of the cancer. Types of cancer are "staged" according to how widespread the cancer is. In the case of melanoma, staging depends on how deep within the skin the tumor is, how large the tumor itself is, and whether the cancer has spread through the skin to other parts of the body. Melanoma starts in the skin cells that make melanin, which is the protective pigment that gives skin color. By the time it reaches stage 3, the melanoma has spread from the skin through the underlying tissue into the lymph nodes closest to the melanoma. Stage 3 melanoma is serious but may be treated with a combination of surgery and other treatments.