General and Systemic Histopathology, C601&C602
    Slide 151: Seborrheic Keratosis of Skin
    It's not real easy to see what we're looking for in this biopsy, although once you recognize it, you'll be surprised how abnormal the epidermis can look.  The thickening of the epidermis involves pretty much the whole surface.  This is a very common skin abnormality.

    See this slide with the virtual microscope.

    This may fool you by looking a bit like cancer, but it's not. This is a very common lesion. You have seen them very likely as dark brown greasy looking spots on the face, and especially around the temple, of older people. Note the hyperkeratosis and acanthosis, that is to say the thickening and hyperplasia of the acanthotic region and keratotic layers of the epidermis. You will also see what appears to be little keratin inclusions cysts in the thickened epidermis. These are often referred to as "pseudohorn" cysts and keratin tunnels. Even though this lesion may look a little spooky, it is really not. Why do you suppose this is not considered malignant? 

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