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
A 56 year old Chronic smoker, mass in bronchus resected. Most useful immunohistochemical marker to make a proper diagnosis would be - 
Select and explain. 
A. Cytokeratin, B. Vimentin, C. Epithelial membrane cadherin, D. Leucocyte common antigen
A: Cytokeratin
Answer: A: Cytokeratin 
Explanation: Mass in bronchus in an old chronic smoker suggest bronchogenic carcinoma. The marker of carcinoma, on immunohistochemistry, is cytokeratin.
Other epithelial markers for carcinoma are :-


Epithelial membrane antigen (EMA):- Breast, lung and Kidney's adenocarcinoma.
Carcino-embryonic antigen: - Carcinomas of GIT, pancreas, lung, breast, uterus and ovary.