ABSTRACT
INTRODUCTION There is a wide clinicopathologic spectrum of epidermal tumors. Some, such as seborrheic keratoses, have a characteristic appearance that can be easily recognized. Others, such as the dermatitic appearance of extramammary Paget disease, can be more difficult. There is also great histologic variability expressed by these epidermal growths. The keratin-filled sac of an epidermoid cyst is diagnosed at low power with a rapid glance. However, the proliferation of atypical keratinizing squamous epithelium can make differentiation of a keratoacanthoma (KA) from a squamous cell carcinoma more subtle.
