A 56 year old Chronic smoker, mass in bronchus resected. Most useful immunohistochemical marker to make a proper diagnosis would be -

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.