At one time, the need for IHC staining on frozen sections was important when antigens were feared to be destroyed by formalin-fixation. However, with the introduction and use of antigen unmasking/epitope retrieval methods for formalin-fixed, paraffin-embedded (FFPE) tissue, use of frozen sections for IHC is much less frequent. Frozen sections are primarily used for IHC only when a quick evaluation is necessary without the delay of fixation, tissue processing, and slide processing.
Adequate fixation of frozen section slides is as important as adequate fixation of FFPE tissue sections. This is done by placing air-dried frozen section slides in cold acetone. To ensure section adhesion, slides should be air-dried 1-2 hours before exposure to the cold acetone. The cold acetone preserves antigenicity, as well as morphology. Since acetone is not aldehyde-based, it does not create protein cross-linkages in the tissue section. Because of this, antigen unmasking/epitope retrieval steps are not needed.
IHC staining methods that are performed on frozen sections do require separate validation to those performed on FFPE sections. These validations must show that the frozen section staining methods are equivalent to protocols for IHC staining of formalin-fixed, paraffin-embedded (FFPE) tissue sections.
