Ref:Harrison&;s principle of internal medicine ,18 th edition, page no. 739 The diagnosis of lung cancer most often rests on the morphologic or cytologic features correlated with clinical and radiologic findings. Immunohistochemistry may be used to verify neuroendocrine differentiation within a tumour, with markers such as neuron specific enolase (NSE),CD56 or neural cell adhesion molecule (NCAM), synaptophysin, chromograin, and Leu7.Cytokeratin 7 and 20 used in combination can help narrow the differential diagnosis; Non-Small Cell Lung Cancer , Small Cell Lung