INVASIVE SQUAMOUS CELL CARCINOMA THAT IS PRODUCING ABUNDANT KERATIN
Neoplasia of keratinocytes, or any other cell line for that matter, can be associated with a variety of observable departures from the normal cell line. Nuclear atypia and  invasive properties come to mind, but there can also be a derangement in function. Inasmuch as normal keratinocytes produce keratin, it is not surprising that abnormal keratin production may occur in some squamous cell carcinomas. The keratin in this case is so abundant that it could be confusing. Intracytoplasmic, amorphous blobs of keratin are seen in some areas, and  targetoid  or concentric intracytoplasmic keratin formation is seen in others. Both combine to form a large amount of extracellular material not unlike the fused mass of keratinous cellular remnants seen in normal trichilemmal keratinization. The best example of the latter is seen in sebaceous (trichilemmal or pilar) cysts.

This is a biopsy from the left temple of an 82 year old male:
 
Composite low power view. The material between the cells is not amyloid.
A high power view showing the cytology of the cells and the production of amorphous blobs of the material. Severe nuclear atypia is present.
A high power view showing a nuclear remnant (NR) plus production of the material that has more of a targetoid architecture. The keratinous material remains after cell necrosis in this case.
High power view of this material having a targetoid configuration.
High power view of the structure shown above as seen with polarized light. Keratin is birefringent and is best seen at the tip of the arrow. There is a small amount demonstrated elsewhere in the tumor. Normal surface keratin is seen at the top of the picture.

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