Immunohistochemical stains were performed on the cell-block. The tumor cells were negative for TTF-1, synaptophysin, CD3, and PAX-5.

On the endobronchial biopsy sample, the tumor cells stained strongly positive for cytokeratin AE1/AE3, cytokeratin CAM 5.2, and CD56. The tumor cells stained negative for Napsin-A, TTF-1, synaptophysin, chromogranin, and p63. The controls stained appropriately. These cytomorphologic and immunohistochemical features were diagnostic of small cell carcinoma of the lung.