Squamous cell carcinoma. An 80-year-old man had a scalp lesion excised, which had been evident for three months. By light microscopy, this was a squamous cell carcinoma with an extensive clear cell component. Electron microscopy revealed typical squamous epithelial carcinoma cells attached by desmosomes and filled with bundles of electron-dense tonofilaments (arrows, A) in the cytoplasm. The clear cell component was comprised of glycogen-rich (B, arrows) squamous epithelial cells. The material for electron microscopy in (A) was processed by a standard method; in (B), the sample was postfixed in potassium ferrocyanide-reduced osmium to highlight glycogen stores which are electron dense (B, arrows). A: ×8,000; B: ×6,000. Original magnifications: (A), ×8,000; (B), ×6,000. (Courtesy of Ann M. Dvorak, MD, Beth Israel Deaconess Medical Center, 330 Brookline Ave, Boston, MA 02215.)