Current WHO criteria for LCNEC diagnosis include (i) neuroendocrine morphology (trabeculae, palisading, organoid nesting and/or rosette formation), (ii) high proliferation rate (>10 mitoses per 10 high-power fields), (iii) extensive geographic necrosis and (iv) IHC expression of at least one neuroendocrine marker (chromogranin-A, synaptophysin, NCAM/CD56) (Fig. 1). The gene discussed is NCAM1; the disease is large cell neuroendocrine carcinoma.