PDCD1LG2 and cancer: In addition to the expected deletion of chr9q, consistent with the loss of heterozygosity of PTCH1, we also detected frequent duplication/amplification of chr9p, encompassing the PDL1 and PDL2 genes (which encode the two immune checkpoint proteins PD-L1 and PD-L2, the overexpression of which enables cancer cells to evade the host immune system).