Epidermal neoplasms commonly present with hyperkeratosis, acanthosis, or papillomatosis. These may manifest clinically as a cutaneous horn, scale, palpable induration, a velvety or filiform appearance, or a smooth lesion raised above the surrounding skin surface. As an example, epidermal nevi tend to be raised and linear in configuration, following Blaschko lines. They may be hyperpigmented, hypopigmented, fleshy, or keratotic in appearance.
Cysts and dermal epithelial neoplasms displace the overlying skin and may produce overlying atrophy, erythema, or telangiectasia. The presence of tumor-associated vascularity lends a red or blue appearance, depending on the speed of blood flow and oxygen saturation of the blood. The presence of cytoplasm lends a yellow appearance due to carotenoids dissolved in the aqueous phase of cytoplasm. A brown appearance most commonly relates to melanin within the epithelial cells and underlying dermis, but can also be a result of dermal hemosiderin or lipofuscin deposition. Lipofuscin dissolved in apocrine sweat often lends a blue appearance to portions of sweat gland tumors as a result of diffraction of light (the Tyndall effect). Sebaceous elements lend a yellow or orange appearance. An appreciation of the color, morphology, and distribution of the lesions will help the physician narrow the differential diagnosis.