Carcinoma in situ of the skin

 
The most common form of CIS in the skin is squamous cell carcinoma in situ (SCCIS), which is a malignant epithelial neoplasm with squamous cell differentiation confined in the epidermis. For the purpose of this study, we will use SCCIS as a prototypical example of CIS of the skin. Thus, in this study, when the term CIS is used unmodified "in the skin," it refers to SCCIS. Normal skin (Fig. 1) and some examples of CIS of the skin are illustrated in the Figures 2 –6.

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View Figure  		Figs. 1A–B  Normal skin. The epidermis is a type of stratified squamous epithelium made up of keratocytes. The cells mature or differentiate orderly from the bottom (basal layer) to spinous cells (spinous layer), to granular cells (granular layer), and finally to cornified anucleated cells (cornified layer).

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View Figure  		Figs. 2A–C  Squamous cell carcinoma in situ, very early stage and small. There is focal aggregation of abnormal keratocytes with large atypical nuclei present within otherwise normal epidermis.

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View Figure  		Figs 3A–C  Squamous cell carcinoma in situ, early stage. The epidermis is slightly acanthotic. Note the decrease of maturation, nuclear enlargement, nuclear variation in size and shape, hyperchromasia, and heterochromasia.

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View Figure  		Figs. 4A-C  Squamous cell carcinoma in situ. As the pictures show, the silhouette of the epidermis is preserved, the boundary of dermoepidermal junction is sharp, and the rete ridges are broad and widened. There is abnormal cornification as exhibited morphologically by a parakeratotic layer at the surface of the lesion. Cytopathologically, nuclei of neoplastic keratocytes are large, crowded, overlapping, and pleomorphic. This abnormal cytology is even seen in the parakeratotic layer (arrow; B). Some neoplastic keratocytes are in mitosis.

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View Figure  		Figs. 5A-C  Squamous cell carcinoma in situ. In this example, there is abnormal cornification as seen morphologically as a thickened parakeratotic layer at the top of the lesion. Mitotic figures, including abnormal ones, can be seen in all layers. The neoplastic cells are distributed more or less evenly throughout of the thickened epidermis with a smooth and sharp demarcation between the epidermis and the dermis. Note the sharp border at the left and the contrast between neoplastic keratocytes and normal-looking ones.

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View Figure  		Figs. 6A–E  Squamous cell carcinoma in situ. Although the lesion is thick and there is marked acanthosis, the silhouette of the epidermis is preserved, the boundary of dermoepidermal junction is sharp, and the rete ridges are widened and merged together. The distribution of neoplastic cells is also more or less uniform throughout the thickened epidermis. Note the presence of single cell necrosis, nuclear pleomorphism, multinucleation, and mitotic figures, including abnormal ones and mitotic figures, including abnormal ones and multinucleation.