High-grade tumor showing histologic features of SCLC on H&E (high N:C ratio, nuclear molding, and finely granular chromatin) and high Ki-67 proliferative index (70%). However, all NE markers (with the exception of rare cells labeling weakly with INSM1) and TTF-1 are negative. Various other markers were initially evaluated to exclude an alternative diagnosis (including p40 to exclude squamous cell carcinoma), and were negative. Subsequently performed POU2F3 provides direct support for the diagnosis of SCLC.
Abbreviations: CHRA chromogranin A, H&E hematoxylin and eosin, IHC immunohistochemistry, N:C nuclear-to-cytoplasmic, NE neuroendocrine, SYN synaptophysin