CD44 and neoplasm: Notably, TREM1+ PMN-MDSCs were also involved in pro-tumor signaling pathways, such as FN1 and ANNEXIN. In the FN1 signaling pathway, the FN1 - CD44 ligand-receptor interaction contributed most significantly, while in the ANNEXIN signaling pathway, the ANXA1 - FPR1 ligand-receptor pair was notably active (Supplementary Fig. 6B, C).