This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
Which among the following is a highly sensitive marker for carcinoma? 
Select and explain. 
A. Cytokeratin, B. Vimentin, C. CD45, D. Calretinin
A: Cytokeratin
Answer: A: Cytokeratin 
Explanation: Essentially all cells of epithelial origin express cytokeratins, which are therefore highly sensitive markers for carcinomas. Ref: Encyclopedia of Cancer, Volume 1 edited by Manfred Schwab, 2008, Page 1496