In fact, this observation is very well in line with existing evidence that S100A9 may serve as a prognostic marker in cancer,27 as well as a novel marker for monocytic MDSC.24 28 Knowing this, we decided to perform flow cytometry analysis in an independent cohort of patients with MM (n=20) undergoing PD-1 blockade. This evidence concerns the gene S100A9 and cancer.