The epidermal component of nodular melanoma consists of epithelioid melanocytes with abundant cytoplasm and large vesicular nuclei with prominent nucleoli. The intraepidermal atypical melanocytes are not seen beyond three epidermal ridges on either side of the tumor nodule - i.e. the epidermal component does not extend laterally in relationship to the dermal component.
The dermal component (shown here) is indistinguishable from the vertical (invasive) growth phase of superficial spreading melanomas. The atypical dermal melanocytes form infiltrating nests or large sheets (as shown here) and show no tendency to maturation. Mitotic activity is brisk. Features of regression are frequently seen. The host immune response is variable. The tumor can display a variety of morphologic patterns, including spindle cell, epithelioid, and balloon cell types and contains variable amounts of melanin.