Concordance of Breast Cancer Biomarker Status between Routine Immunohistochemistry/In Situ Hybridization and Oncotype DX qRT-PCR with Investigation of Discordance, a Study of 591 Cases.

Abstract Patients with estrogen receptor (ER)+/HER2-, lymph node-breast cancer with high recurrence risk benefit from adjuvant chemotherapy in addition to hormonal therapy. This study compares ER, progesterone receptor (PR), and HER2 status between routine immunohistochemistry (IHC)/in situ hybridization (ISH) and Oncotype DX (ODX) in 591 cases. ODX recurrence score (RS) and clinicopathologic features were compared between ER/PR-concordant and discordant cases. H&E slides from ER discordant cases were reexamined. Concordance was high between ODX and IHC for ER status (580/591, 98.1%) and moderate for PR status (512/591, 86.6%). All 11 ER discordant cases were ER+ by IHC but ER-by ODX and high risk by ODX. Histologically, all of these cases were grade III invasive ductal carcinoma (IDC), except one case diagnosed as IDC with apocrine features. Although this case was grade I and ER/PR+ by IHC, this patient received chemotherapy due to high RS. Of 79 PR discordant cases, 60 were PR+ by IHC but PR-by ODX. 584 cases had available HER2 data, with high negative agreement (580/582, 99.7%). However, both HER2+ cases by ISH were HER2-by ODX. Mean RS was higher for ER discordant than concordant cases (48.0 versus 17.1, p value