PDCD1 and neoplasm: Analysing the distribution of the immune checkpoint molecules in the different CMS subgroups more closely further revealed an increased fraction of Tcyt cells expressing PD-1 in CMS1 tumours, but also in selected CMS3 and CMS4 tumours, while increased fractions of Tcyt cells expressing CTLA-4 was found mainly in selected CMS3 tumours (Figure 3b).