12P Updated findings from the first prospective HER2DX clinical decision impact study on early-stage HER2-positive (HER2+) breast cancer (BC)

HER2DX is a genomic test that provides prognostic (HER2DX risk score) and predictive information (pCR score) in HER2+ early BC. Here, we report an update of the results of the first ongoing decision impact study of HER2DX at Hospital Clinic of Barcelona. We conducted an observational, prospective, pilot, unicentric study, since Nov/21 (ongoing), to analyze the impact of HER2DX in clinical practice in early-stage HER2+ BC. Any medical oncologist of the Breast Unit could order the test. A survey was completed by the treating physician before and after receiving the result of HER2DX. The main objective was to assess the % of change in the therapeutic plan after obtaining the HER2DX report. We also assess the change in the physician´s confidence before and after the test. Due to the exploratory nature of the study, there was no sample size calculation. Descriptive statistics were used. We report the results after the inclusion of 128 pts (as of 27th of Jan/24). Median age was 54 (range 30-90) and 55% of pts were postmenopausal. Most pts had stage I (37%) or II (48%), grade 2 (51%) or 3 (42%), ductal histology (85%), hormone receptor positive (62%), median Ki67 of 35 (range 3-90) and median TILs of 12 (range 0-90). 77% of pts received neoadjuvant therapy and 23% upfront surgery. Any change in the treatment plan before and after the HER2DX result was observed in 71 of 128 (55%) of the cases. Among them, 34% (n=24) of pts escalated therapy (7/24 used more intense chemotherapy (CT), 8/24 added another antiHER2 and 9/24 escalated both CT and antiHER2). A de-escalation strategy was noted in 66% (n=47) of the pts who changed the therapy. Among them, 18/47 received less intense CT, 18/47 less anti-HER2 and 11/47 both less CT and antiHER2. In pts who de-escalated the antiHER2, 23/29 received less antiHER2 (i.e. avoidance of pertuzumab or neratinib) and 6/29 shortened the duration of trastuzumab. In a scale from 1 (very unconfident) to 5 (completely confident), the mean confidence of physicians improved after the test (3.8 vs 4.6, p=0.002). In this first prospective study, HER2DX impacted clinical care in early-stage HER2+ BC and improved the level of confidence of physicians.