This 3B Scientific® Skin Pathology model shows healthy skin and 5 different stages of malignant melanoma on the front and back, enlarged 8 times:
healthy
malignant cells are found at the surface, within the epidermis
malignant cells fill the epidermis, a few invade the papillary layer
malignant cells fill the papillary layer
malignant cells invade the reticular layer
malignant cells have reached the subcutaneous fatty tissue, satellite cells approach a vein