Trastuzumab plus pertuzumab for HER2-amplified advanced colorectal cancer: Results from the drug rediscovery protocol (DRUP)

Background: In 2-5% of patients with colorectal cancer (CRC), human epidermal growth factor 2 (HER2) is amplified or overexpressed. Despite prior evidence that anti-HER2 therapy confers clinical benefit (CB) in onethird of these patients, it is not approved for this indication in Europe. In the Drug Rediscovery Protocol (DRUP), patients are treated with off -label drugs based on their molecular profile. Here, we present the results of the cohort 'trastuzumab/pertuzumab for treatment -refractory patients with RAS/BRAF-wild-type HER2amplified metastatic CRC (HER2+mCRC)'. Methods: Patients with progressive treatment -refractory RAS/BRAF-wild-type HER2+mCRC with measurable disease were included for trastuzumab plus pertuzumab treatment. Primary endpoints of DRUP are CB (defined as confirmed objective response (OR) or stable disease (SD) >= 16 weeks) and safety. Patients were enrolled using a Simon -like 2 -stage model, with 8 patients in stage 1 and 24 patients in stage 2 if at least 1/8 patients had CB. To identify biomarkers for response, whole genome sequencing (WGS) was performed on pre-treatment biopsies. Results: CB was observed in 11/24 evaluable patients (46%) with HER2+mCRC, seven patients achieved an OR (29%). Median duration of response was 8.4 months. Patients had undergone a median of 3 prior treatment lines. Median progression -free survival and overall survival were 4.3 months (95% CI 1.9-10.3) and 8.2 months (95% CI 7.2-14.7), respectively. No unexpected toxicities were observed. WGS provided potential explanations for resistance in 3/10 patients without CB, for whom WGS was available. Conclusions: The results of this study confirm a clinically significant benefit of trastuzumab plus pertuzumab treatment in patients with HER2+mCRC.