<prompt> 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:CytokeratinParvalbuminHMB-45Hep-par1  <response>: 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. Histologically, this tumor is characterized by the presence of keratinization andor intercellular bridges. HMB melanoma, Hep par1 liver cancer and parvalbumin schizophrenia. 