ABSTRACT
We have studied 49 breast cancers in order to evaluate the Ki-67 polyclonal antibody in immunohistochemical assessing of the proliferating cell index on paraffin embedded tissue sections. Polyclonal Ki-67 immunostaining has been compared with monoclonal Ki-67 immunostaining on frozen sections. This study has been performed on two groups of breast cancers: the first using a prospective method including 22 consecutive cases observed in 1994; the second one, in a retrospective analysis of 27 consecutive cases observed in 1987-1988. Frozen section have been shortly fixed with formalin, methanol and acetone and subsequently processed with Ki-67 monoclonal antibody. The paraffin sections, routinely fixed in formalin and embedded in paraffin, have been pretreated in a microwave oven before processing with Ki-67 polyclonal antibody. The proliferating cell index, expressed in a semi-quantitative evaluation as percentage of stained nuclei, resulted differently in the mean and in the median values between the frozen and the paraffin groups. The difference is bigger and significant in the retrospective group observed in 1987-88. On the contrary, the results obtained from frozen and paraffin sections of the prospective group observed in 1994 are comparable. The prospective and the retrospective groups significantly differ in the fixation time. In 1994 the specimens were fixed for no more than 36 hours while previously the fixation time wasn't standardized and often exceeded 36 hours. The Ki-67 polyclonal antibody on paraffin sections is comparable to the Ki-67 monoclonal antibody on frozen sections on condition that fixation is strikingly standardized. The immunostaining with vimentin as antigenicity preservation control is also advisable.
