Immunohistochemistry of breast tumor markers on archived bouin-fixed paraffin-embedded tissues

Neutral-buffered formalin is the most commonly used tissue fixative in pathology laboratory. Among other fixatives, Bouin's solution has been used in several laboratories and is still in use for particular tissues. In this project, we determine if we can study breast clinical markers on archived Bouin-fixed tissue samples with immunohistochemistry (IHC) protocols optimized for tissue fixed in neutral-buffered formalin. To evaluate the concordance of IHC results between formalin-fixed and Bouin-fixed tissues, we calculated the concordance percentage and the κ statistic of 12 clinical IHC markers quantified by an automated system on breast cancer tissues fixed in neutral-buffered formalin and their corresponding tissues fixed in Bouin's solution. When positivity threshold of immunostaining was setup at ≥10% for both fixation conditions, we observed a concordance percentage of 83.9% (κ=0.65). However, when positivity threshold of immunostaining was lowered to 3% to 4% for Bouin-fixed tissues, concordance percentage was then of 96.8% (κ=0.92). Our data demonstrate that we can study IHC markers on archived Bouin-fixed tissue from patients with long clinical follow-up using IHC protocols optimized for formalin-fixed tissues after an adjustment of the positivity threshold of immunostaining quantified by an automated system.