The use of exosome and immune profiling to analyze a phase 2 study on the addition of patritumab or placebo to cetuximab and a platinum agent for recurrent / metastatic head and neck cancer (R/M HNSCC) patients.

6043Background: The use of patritumab (Daiichi Sankyo), an internalizing anti-HER3 monoclonal antibody, in combination with cetuximab and cisplatin was investigated in a cohort of patients with R/M HNSCC in a Phase II trial (NCT02633800). We investigated the EGFR-HER3 dimer (an established marker of cetuximab resistance within a previous study) in the circulating exosomes from patients enrolled in this trial. The objective was to identify non-invasive treatment stratification and longitudinal monitoring markers. Since antibody-directed cytotoxicity is involved as a mechanism of action for these therapies, exosomal microRNAs (miR21 and miR142), which promote the expansion of functional myeloid-derived suppressor cells (MDSC), as well as other suppressive adaptive and innate immune cell components are postulated as potential immune monitoring parameters. Methods: We extracted exosomes from patient serum at 2 timepoints: pretreatment (c1) and pre-cycle 2 (c2, day 1). Exosomes were stained with fluorescently ...