69-year-old man comes for evaluation of a 1-week history of difficulty swallowing. He has a 10-year history of acid reflux disease controlled with antacids as needed. He does not smoke cigarettes or drink alcoholic beverages. Physical examination shows no abnormalities. Results of a barium swallow test are positive. Endoscopy shows a fungating mass in the lower portion of the esophagus. A biopsy specimen of the mass is obtained, and an immunohistochemical stain is applied.
The antibodies used in this stain are specific for which of the following proteins?
A. Cytokeratin
B. Desmin
C. Desmoglein
D. Tubulin
E. Vimentin