ER and PR Immunohistochemistry and HER2 FISH versus Oncotype DX: Implications for Breast Cancer Treatment

Estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor (HER2) concordance between immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH), and Oncotype DX, a commercially available RT‐PCR‐based assay which recently began reporting biomarker results was assessed. ER concordance was 98.9% (262/265), Pearson correlation coefficient (r) = 0.42, and Spearman's rank correlation (ρ) = 0.25. Positive percent agreement for ER was 98.9% (262/265). One patient with discordant ER results was not offered hormone therapy based on the preferential use of Oncotype DX. PR was concordant in 91.3% (242/265), r = 0.80, ρ = 0.75, and Cohen's kappa (κ) = 0.63. Positive percent agreement for PR was 90.5% (218/241) and negative percent agreement was 100% (24/24). HER2 concordance was 99.2% (245/247), r = 0.35, ρ = 0.28, and κ = 0.12. Positive percent agreement for HER2 was 0% (0/2) and negative percent agreement was 100% (245/245). Of the three FISH HER2‐amplified cases, two were negative and one was equivocal, and all FISH HER2‐equivocal cases (n = 3) were negative by Oncotype DX. Patients that were FISH HER2‐amplified, Oncotype DX HER2‐negative did not receive trastuzumab. Although our results demonstrated high concordance between IHC and Oncotype DX for ER and PR, our data showed poor positive percent agreement for HER2. Compared to FISH, Oncotype DX does not identify HER2‐positive breast carcinomas. The preferential use of Oncotype DX biomarker results over IHC and FISH is discouraged.