Examination of a skin lesion demonstrates very abnormal squamous cells with a high nuclear/cytoplasmic ratio and clumped chromatin. These cells form nests within the epidermis that extend to the superficial surface of the epithelium. In some places, nests of these cells have central areas of abnormal keratin formation. The basement membrane is intact and no nests of cells are seen in the dermis. Which of the following terms best describes this lesion?

The lesion is an example of carcinoma in situ. The presence of keratin pearls and the distribution of abnormal cells all the way to the top of the epidermis distinguish this lesion from simple dysplasia, in which abnormal cells are seen only in the lowermost layers of the epidermis. Invasive carcinoma would be indicated by a disruption of the basement membrane or the presence of nests of cells in the dermis. The term metaplasia is used when a normal epithelium is replaced by another mature, differentiated epithelium. Ref: Wyatt C., Butterwoh IV J.F., Moos P.J., Mackey D.C., Brown T.G. (2008). Chapter 4. Neoplasia. In C. Wyatt, J.F. Butterwoh IV, P.J. Moos, D.C. Mackey, T.G. Brown (Eds), Pathology: The Big Picture.