CBX4 and cancer: Chromobox homologue 4 (CBX4), also known as polycomb 2 (PC2) or NBP16, is located on chromosome 17q25.3 and encodes a polycomb repressive complex 1-associated protein (CBX4 protein) that is a member of the Polycomb group (PcG) of proteins.7 PcG proteins are transcriptional repressors that are mainly involved in regulating development, senescence, stemness, and cancer progression.8 The balance in PcG gene penetrance is crucial for proper stem cell homoeostasis and the prevention of CSC development.