Melanoma can spread very quickly, and the rate of spread depends on various factors unique to each individual and their cancer. Once a melanoma spot reaches the size of a dime on your skin, it has a 50% chance of spreading. Melanoma can grow extremely quickly and can become life-threatening in as little as six weeks if left untreated. It can spread to almost any area of the body, including lymph nodes, lungs, liver, bones, brain, and gastrointestinal tract. Melanoma is staged from 0 to 4, and the lower the number, the less cancer has spread. The five-year survival rate for people with melanoma is about 99% if the cancer is detected early, but it drops to about 15% if the cancer has spread to other parts of the body. Once a tumor has spread to distant body sites such as organs, it is considered a stage IV melanoma, with an estimated five-year survival rate of only 18% in the US.