NCIt definition : A melanoma that arises from the skin, conjunctiva, and mucosal sites. It is characterized
by a vertical growth phase and lacks a significant radial growth phase. It may or
may not arise from a pre-existing nevus. Morphologically, it is characterized by the
presence of cohesive aggregates of neoplastic melanocytes in the dermis that often
exhibit an epithelioid appearance. The overlying epidermis is often involved.;