NCIt definition : A melanoma that arises from the skin 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.;