Beatson et al. have shown that MUC1-ST interacts with the sialic acid-binding protein Siglec-9 expressed on monocytes and macrophages: this interaction induces the development of tumour-associated macrophages showing increased expression of the PD-L1 checkpoint ligand as well as other proteins associated with tumour growth and metastases [53]. Here, MUC1 is linked to neoplasm.