Furthermore, ID1, but not ID3 expression, was also found to be on average threefold higher (and up to ninefold higher) in PBMCs from patients with metastatic breast cancer (n=7) and colorectal cancer (n=6) compared with healthy, age-matched controls (n=10, Mann–Whitney test; P<0.01; Supplementary Fig. 6A,B). Here, ID3 is linked to colorectal cancer.