Ki-67 immunostaining in neuroendocrine carcinoma

Photomicrographs (400x) of sections of neuroendocrine carcinoma immunostained for the Ki-67 antigen with the MIB-1 monoclonal antibody and counterstained with hematoxylin. Ki-67 immunopositivity is >20% by definition in neuroendocrine carcinomas, but may vary considerably: The panels depict two patients where Ki-67 positivity was 40% (A) versus 90% (B).