Superficial spreading melanoma, light micrograph. Superficial spreading melanoma (SSM) is the most common subtype accounting for almost 70% of all cutaneous melanomas. This light photomicrograph shows the radial growth phase, which consists of proliferation of atypical melanocytes arranged singly or in clusters throughout all levels of epidermis. The appearance is similar to Paget's disease. The tumour cells are epithelioid with abundant cytoplasm, pleomorphic nuclei, prominent nucleoli, frequent mitoses, and dusty melanin pigmentation. Note the dermal melanophages.