"Why is malignant melanoma so dangerous?

"Why is malignant melanoma so dangerous?Of the three most common skin cancers, malignant melanoma represents the only truly life-threatening form. As mentioned earlier, this disease stems from melanocytes, the cells that produce melanin in response to UV radiation. Initially, melanoma spreads along the surface of the skin. This is called the horizontal growth phase. This growth phase can last months to years, depending on the type of melanoma involved. The melanoma subsequently begins to invade the skin in a process called the vertical growth phase. During this phase of growth, the melanoma cells gain access to blood and lymphatic vessels, allowing the cells to travel to other parts of the body. After the melanoma cells spread, the chance for cure decreases significantly. The melanoma cells invade normal tissues and destroy them by infiltrating and replacing the normal cells. In contrast, the great majority of basal and squamous cancer cells don’t have this ability to spread and therefore only invade locally. This distinction accounts for the substantial difference in prognosis between the different types of skin cancers."Author(s): McClay, Edward F. MDMcClay, Mary-Eileen T.