For example, the same mutational signatures that arise from passenger mutations during oncogenesis are present in a broad range of cancer types—signature 2 has been found in 22 cancer types and attributed to the activity of the AID/APOBEC family of cytidine deaminases [30•]—and could enable cancer diagnoses that reflect the aetiology in a tumour-agnostic manner. This evidence concerns the gene CDA and cancer.