MPO and neoplasm: Interestingly, we observed that increased STAT3 expression in tumor tissue was positively correlated with the expression of neutrophil-specific markers in both cancer types (NCF2 for HNC and CD66b, MPO, and NCF1 for melanoma), suggesting that neutrophils play a role in the high expression of STAT3 in tumors (Fig. 1b and Supplementary Fig. 1b–d).