(typical vertial growth)
In this field (same lesion as Fig. 16), small nests and individual tumor cells infiltrate the reticular dermis among collagen bundles of the reticular dermis. Inflammatory infiltrates are not associated with this population of neoplastic migrants. The cells have abandoned the security of a community of cells (level III invasion) for the hazards of a migration (level IV invasion; level IV pattern0.
In this more advanced pattern of growth, the clustered small nests and the individual cells form an ill-defined, small expansile nodule. In this limited area, it is by pattern, rather than its small size, tjat such an area can be appropriately characterized as melanoma. Obviously, this is level IV invasion; it is representative of a more advanced pattern of neoplastic progression; the cells have acquired the properties of universal migrants. The patient should be examined and followed. Some consideration should be given to sentinel node biopsy.