A 67 yr male with history of chronic smoking hemoptysis with cough. Bronchoscopic biopsy from centrally located mass shows undifferentiated tumor histopathologically. Most useful I.H.C. (immunohistochemical) marker to make a proper diagnosis would be

• The presence of chronic smoking, cough and hemoptysis in old man is a pointer towards a diagnosis of bronchogenic cancer. The central location suggests the possibility of a squamous cell cancer. • Robbins writes “Histologically, this tumor is characterized by the presence of keratinization and/or intercellular bridges”. Other options: HMB (melanoma), Hep par1 (liver cancer) and parvalbumin (schizophrenia).