CytoLyt fixation significantly inhibits MIB1 immunoreactivity whereas alternative Ki-67 clone 30-9 is not susceptible to the inhibition: Critical diagnostic implications.

Background: The Ki-67 proliferation marker has multiple diagnostic and prognostic applications. Although several clones to the Ki-67 antigen are commercially available, the MIB1 clone is widely recommended in the surgical pathology literature for neuroendocrine tumors. In our cytopathology practice, we have encountered unexpectedly low MIB1 immunoreactivity in CytoLyt-fixed cell blocks (CBs).