MKI67 and small cell lung carcinoma: Definitive diagnosis was confirmed through bronchoscopic biopsy and immunohistochemistry (Fig. 3A and B), revealing SCLC with the following profile:LCA-negative, TTF-1-positive, NapsinA-negative, focal chromogranin A expression, synaptophysin-positive, CD56-positive, INSM1-positive, pan-cytokeratin-positive, P40-negative, and Ki-67 proliferation index of 90%.