Narrator: Melanoma may be diagnosed when a skin irregularity, thought to be a mole, becomes cancerous. The seriousness of the cancer is based primarily on tumor thickness.

Melanomas generally fit into two categories. The first group includes cancers that have not spread beyond the area bordering the skin irregularity. Wide surgical tumor removal is typically used for these cancers, and it's often effective. The tumor and a large area of surrounding normal skin are outlined by an elliptical border and then removed. Here, normal tissue is visible surrounding the tumor.

The second broad category of melanomas are those which progress beyond the visible cancer growth. Growth deeper into the skin may allow cancer cells to enter the small lymphatic vessels. There they may travel to distant locations in the body.

Cancer cells commonly migrate to a draining lymph node. Melanoma cells may reside undetected in the immune tissue for some time. If melanoma escapes immune system defenses, it can travel to other body sites. Here, an example of tumor spread to the lung is shown.