High ICOS (⩾75 percentile RNA rank) was present in 14% of 514 cancers and independently associated with high PD-1 (p = 0.025), PD-L1 (p < 0.0001), and CTLA-4 RNA expression (p < 0.0001) and with patients not having colorectal cancer (p = 0.0009; multivariate analysis). The gene discussed is CTLA4; the disease is cancer.