Small cell lung carcinomas (SCLC) show variable positivity for neural markers such as neurofilament, Leu7, chromogranin, synaptophysin, NCAM/CD56 (cell membrane staining; very sensitive but less specific; shown here), and neuron-specific enolase. Upto 10% of SCLC may be completely negative for neuroendocrine markers. SCLC is positive for low molecular weight keratins (dot-like paranuclear or diffuse cytoplasmic staining) but negative for high molecular weight keratins. BCL2 is expressed often. It is negative for CD99 (in contrast to Ewing Sarcoma/PNET). TTF-1 is positive in vast majority of cases whereas Napsin A is negative (marker of adenocarcinoma differentiation). CD117 (c-KIT) is expressed in about 60% of cases. Ki-67 proliferation index is 80-100%. Ultrastructurally, there are dense-core secretory granules in at least a few cells in the majority of cases of small cell carcinoma.