The Clark level is a measure of depth of invasion into the skin used as a prognostic indicator for skin cancers: level I: confined to the outermost layer of the skin, epidermis; level II: penetration into the dermis; level III to IV: invasion through the dermis into deeper dermal layers, yet still confined to the skin; level V: penetration through the dermis and into the fat and hypodermis.

 Skin Cancer