To prove this hypothesis, we first analyzed RNA microarray data from the METABRIC human breast cancer cohort (online supplemental figure S1A).16 Here, we found a significant positive correlation between the RNA expression levels of formyl peptide receptor 1 (FPR1), an established marker gene of neutrophils, and of CXCR4, whose gene product increases during neutrophil aging on the surface of these immune cells,10 with higher tumor stages. Here, CXCR4 is linked to breast carcinoma.