Figure 1.

Representation of the progression from healthy melanocyte, to the radial growth phase (RGP), to the vertical growth phase (VGP), to metastatic (MET) melanoma. (A) Healthy melanocytes exist in a fixed ratio to keratinocytes in the basal layer of the epidermis; (B) RGP cells exhibit uncontrolled cell division and over-production of melanin; (C) VGP cells can spread throughout the epidermis and no longer respond to proliferation, inhibiting cytokines; and (D) MET cells are able to break through the basement membrane and enter the circulation.