74P Assessing the implementation of the HER2DX genomic test in a real-world setting for HER2-positive breast cancer

HER2DX genomic test is a valuable tool in clinical practice for patients (pts) with early-stage HER2+ breast cancer (BC). This study aims to share insights from the application of the test in a real-world setting, following its adoption in clinical use. This is the first analysis of 214 HER2DX tests performed in consecutive pts with HER2+ BC. HER2DX were conducted at a central lab in Spain (2022-2023). We focused on evaluating the turn-around time, success rate, and outcomes of the test. Results were correlated with clinical-pathological parameters (tumor size, nodal status, estrogen receptor (ER), Ki67, and TILs). We utilized chi-square tests and Student's t-tests. Cohort consisted of 214 pts (95% from Spain), median age of 56 years (range 32-90). ER+ were 71.1%, 59% had grade 2, 90% were invasive carcinoma NST and 5% lobular. Stage I, II, IIIA-B-C, IV disease represented 31.3%, 50.5%, 11.2%, 2.8%, 1.4% and 2.8%, respectively. Mean Ki67 was 35.8% and TILs were 16.0%. 74.8% were core needle biopsies. The success rate of tissue processing was 98.6%, and from there to generating a test report was 100%. Average turnaround time from receiving FFPE samples to reporting was 8.1 working days. Proportion of HER2DX high- and low-risk was 45.3% and 54.7%, respectively (varied according to clinical stage, except for stage II). Statistically significant differences in terms of grade and Ki67 was observed between HER2DX high- and low-risk, but not age, ER or TILs. In stage I, HER2DX high-risk according to a lower cutoff (i.e., 32) represented 26.9% of cases. Distribution across HER2DX pCR-high, -medium, and -low groups was 30.8%, 27.1%, and 42.1%, respectively. Significant differences in ER status, Ki67, TILs and grade were observed between HER2DX pCR-high and -low groups. Among the 10 lobular carcinomas, 90% were HER2DX pCR low/med, and 90% HER2DX low-risk. Finally, 15% of all tested cases had HER2DX ERBB2-low, and 88% (28/32) of them had HER2 2+. Implementation of the HER2DX test is feasible and is being used across a wide range of clinical scenarios. The moderate alignment of HER2DX scores with standard clinical-pathological metrics, fitting expected patterns, provides new and meaningful insights for healthcare providers and pts.