Melanoma cancer. Coloured transmission electron micrograph (TEM) of a section through human skin showing cancer cells (small black/green dots). These are melanocytes, the cells that produce the brown pigment melanin in the skin. Cancer cells undergo continuous division, growing chaotically and forming tumours that can impair the normal functioning of the affected organ. Melanoma cells are highly malignant, invading and destroying surrounding tissues and migrating (metastasizing) to other parts of the body, where they seed secondary tumours. Treatment is by excision, followed by radiotherapy or chemotherapy if the cancer has spread. Magnification unknown.