Superficial Spreading Melanoma
The radial phase of superficial spreading melanoma (SSM) shows proliferation of atypical melanocytes arranged singly or in clusters throughout all levels of epidermis. The appearance is similar to Paget's disease. The tumor cells are epithelioid with abundant cytoplasm, pleomorphic nuclei, prominent nucleoli, frequent mitoses, and dusty melanin pigmentation. The atypical melanocytes are also present in the outer layers of the hair follicle in this image. Note the dermal melanophages. The invasive component, when present, is epithelioid as well.
With SSM, there is usually little or no actinic damage. The epidermis is acanthotic and there is partial or complete loss of rete ridges.