CDA and cancer: The discovery of cytidine deaminase enzymes such as A3A and/or A3B as a major source of mutation is ground-breaking not only in revealing a mechanism of somatic hypermutation in cancer genomes, but in revealing possible therapeutic targets for common forms of cancer, targets that spare normal cells because: 1) APOBEC enzymes are oftentimes over-expressed in cancer cells and not normal cells [13] and 2) they are non essential enzymes, so transitory or temporary inhibition of their activity may have little effect on normal cells [9].