In this phase II clinical trial with an explorative nature, the efficacy of the combination of monalizumab and trastuzumab is assessed in patients with metastatic or locally incurable HER2-positive breast cancer. Clinical efficacy will be assessed in patients with high stromal tumor-infiltrating lymphocytes (sTILs) or low sTILs in two separate cohorts (higher or equal to 5% versus lower than 5%). Since the combination of monalizumab and trastuzumab has not been administered before, dose limiting toxicities (DLTs) will be monitored throughout the trial using the Pocock-type boundary rules for continuous monitoring of toxicity in phase II trials.~In the first stage, 11 patients will be accrued per cohort. If there are 1 or fewer responses in these 11 patients, the study will be stopped. Otherwise, 8 additional patients will be accrued for a total of 19 patients.~The study will start with two cohorts (sTILs high and sTILs low), a total of 22 (2x11) patients will be included in the first stage. Dependent on the interim analysis (continuation of no cohorts, 1 or 2 cohorts), a maximum of 38 patients will be included.
In this phase II clinical trial the efficacy of the combination of monalizumab and trastuzumab is assessed in patients with metastatic or locally incurable HER2-positive breast cancer