Estrogen receptor (ER), progesterone receptor (PR), and HER-2/neu studies are variably submitted for pathology review but are influential in treatment choices for breast cancer patients seeking second opinion or transferring care.
To determine the frequency of interinstitutional discordance for the interpretation of ER/PR and HER-2/neu immunohistochemical slides and assess the resulting clinical significance.
One thousand one hundred thirty-nine ER, 1111 PR, and 663 HER-2/neu immunohistochemistry stains from 1139 cases were reviewed at contributing and referral centers and compared for concordance and clinical impact of discordance.
Interinstitutional concordance for individual stains was excellent (ER: κ = 0.93; PR: κ = 0.90; HER-2/neu: κ = 0.93). One hundred four (9.1%) had interinstitutional discordance in 1 or more stains; however, the majority of the discordance was clinically insignificant. Seven patients (0.6%) had a clinically significant change in treatment recommendation based on review and 2 (0.2%) had interpretation changes that would likely have resulted in treatment change had they not already completed therapy. Two patients (0.2%) had change in treatment despite concordant interpretations.
Overall, there was excellent interinstitutional concordance for pathology review of ER, PR, and HER-2/neu immunohistochemistry stains. However, a small but significant number of patients (0.8%) received potential benefit from review, justifying inclusion of these slides along with other pathology slides to be reviewed for all breast cancer patients being seen at another institution who have not yet completed hormonal and/or chemotherapy.