[Tumors developing in an epidermal cyst].

The paper presents clinical and morphological characteristics of neoplasms arising in epidermal cysts (73 observations). It is emphasized that the epithelium of epidermal cyst may be the source of growth of not only benign cystic epithelioma ("proliferating epidermal cyst" as designated by the foreign authors) but also of squamous cell carcinoma. Cystic epithelioma (54 observations) is a slowly growing tumor represented by outgrowths in the cyst lumen of differentiated squamous epithelium apt to form smaller cysts. A predominance in cystic epithelioma of the basal type cells and complexes of squamous epithelial cells with hyperchromic and slightly polymorphous nuclei (7 observations) is considered to be the initial sign of malignancy of the noninvasive cancer type. Cancer arising in epidermal cyst (11 observations) is characterized by rapid growth, invasion into derma and trend for relapses. Frequently it has the structure of keratinizing squamous cell carcinoma. A malignant tumor is described characterized by a combination of cystic epithelioma, squamous cell carcinoma of pseudosarcomatous structure in some areas and glandular formations whose origin is obscure.