Abstract PO5-02-09: Discordance of the PAM50 intrinsic subtypes with the immunohistochemistry-based subtypes in HER2-negative early breast cancer treated with neoadjuvant chemotherapy

Abstract Background The PAM50 (Prosigna Breast Cancer Gene Signature Assay) can be used to assess the expression levels of 50 genes in early breast cancer biopsies, including formalin-fixed paraffin-embedded (FFPE) tissue from human epidermal growth factor receptor 2 (HER2)-negative patients. However, there is currently no practical molecular assay for intrinsic subtype in real-world practice that addresses the problems of cost and run-time. Methods In the phase 2 HER2E-PAM/PAMILIA study (NCT04817540), we prospectively analyzed molecular subtyping through the PAM50 test in low HER2 (HER2 IHC 1+ or 2+ SISH-) breast cancer patients. PAM50 intrinsic subtypes were determined according to 50 cancer genes using the NanoString nCounter Analysis System. This study was originally designed to determine whether adding HER2-targeted treatment in HER2 enriched molecular subtype increases the pathologic complete rate (pCR). We aimed to analyze the discordance between immunohistochemistry (IHC)-based surrogate subtyping of pre- 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-02-09.