Smith

 
"The principal histologic criterion for the diagnosis [of melanoma] is the presence of dermal invasion by atypical melanocytic cells (melanoma cells) from the overlying epidermis. In most tumors, the atypical cells within the epidermis are arranged in nests or clusters at the epidermal-dermal junction; however, individual cells or a row of cells may be present. If the cells are confined to the epidermis, but show definite atypical cytologic features, the designations atypical junctional nevus and melanoma in situ are used. Not until the atypical cells have actually invaded the dermis is the lesion diagnosed as a malignant melanoma." Smith Jr JL. Pigmented nevi and malignant melanoma. In: Graham JH, Johnson WC, Helwig EB. Dermal Pathology. Maryland: Harper and Row Publishers, Inc., 1972:491.
 

Brief Critique

 
As mentioned already, the notion of invasion being recognizable morphologically is fallacious. The phrase "atypical junctional nevus" does not convey anything meaningful, especially in the context of that nevus being employed as a synonym for melanoma in situ. The other findings mentioned by Smith are of no assistance in coming to a specific diagnosis of melanoma, all of them being noted not uncommonly in Spitz's nevi.