%0 Journal Article
%T Impact of the OncotypeDX score and HER2 RNA PCR levels on HER2-low IHC levels in primary and metastasized tumors.
%A Feldman D
%A Sinberger LA
%A Salmon-Divon M
%A Ben-Dror J
%A Shachar SS
%A Sonnenblick A
%J BMC Cancer
%V 23
%N 1
%D 2023 Oct 24
%M 37875892
%F 4.638
%R 10.1186/s12885-023-11530-w
%X <B>OBJECTIVE: </B>One-half of hormone receptor-positive (HR +) breast cancer (BC) patients have low expression of HER2 (HER2-low) and may benefit from trastuzumab deruxtecan (TDXd). This study aimed to identify parameters associated with HER2-low levels in primary and metastatic tumors. We specifically sought to determine whether OncotypeDX and HER2 mRNA levels could identify patients who would otherwise be considered HER2-negative by immunohistochemistry (IHC).<BR><B>METHODS: </B>This retrospective analysis of all consecutive HR + patients who underwent OncotypeDX from January 2004 to December 2020 was conducted in a single medical center (n = 1429). We divided HER2-negative cases into HER2-low (IHC = 1 + or 2 + and non-amplified fluorescent situ hybridization) and HER2-0 (IHC = 0). HER2 RT-PCR was evaluated from the OncotypeDX results.<BR><B>RESULTS: </B>HER2-low cases exhibited significantly higher HER2 RT-PCR scores (p = 2.1e-9), elevated estrogen receptor (ER) levels (p = 0.0114), and larger tumor sizes compared to HER2-0 cases (> 2 cm; 36.6% vs. 22.1%, respectively, p < 0.00001). Primary tumors > 2 cm were more likely to be HER2-low (OR = 2.07, 95% CI: 1.6317 to 2.6475, p < 0.0001). Metastatic BCs expressed higher HER2 IHC scores compared with primary BCs (Wilcoxon signed-rank, p = 0.046). HER2 IHC scores were higher for low-risk vs. medium-risk OncotypeDX (p = 0.0067). No other clinical or pathological parameters were associated with the increase in HER2 levels in the metastatic samples.<BR><B>CONCLUSIONS: </B>It might be beneficial to use clinical data from the primary tumor, including the HER2 RT-PCR score, to determine a HER2-low status.