Analysis of the muscle invasive bladder cancer (BLCA) cohort from The Cancer Genome Atlas (TCGA) (20) identified 31 different JAK1 variants in 25/412 TCGA BLCA samples, including single nucleotide variants predicted to alter JAK1 protein function and non-sense/frameshift variants predicted to impair JAK1 signaling (Figure 1A). Here, JAK1 is linked to bladder transitional cell carcinoma.