Danger of Malignant Melanoma and how you can spot it:

There are three forms of cancer of the skin or skin cancer. The most dangerous of all is a cancer in the melanocytes. Skin cancer in the melanocytes form a tumor in those cells that produce melanin, which is a substance which helps to color your skin. Compared to other skin cancers, Malignant Melanoma is a more rare type of skin cancer, but is most fatal. This means that we need to do anything and everything to spot, diagnose and treat in its early stages. Below is a list of ways to help you recognize it in its early stage.

A.One half is unlike the other half.
B.An irregular, scalloped or poorly defined border.
C.Is varied from one area to another; has shades of tan, brown, or black; or is sometimes white, red or blue.
D.Melanomas usually are greater than 6mm (the size of a pencil eraser) when diagnosed, but they can be smaller.
E.A mole or skin lesion that looks different from the rest or is changing in size, shape or color.
http://www.health-wellness-care.com/html/health_articles/malignant_melanoma.html
http://www.aad.org/skin-conditions/skin-cancer-detection/about-skin-self-exams