APOBEC3B and neoplasm: To test the idea that the lack of tumor phenotypes in our original R26-A3B model16 may be due to low expression levels, we established a new C57BL/6 mouse model for inducible expression of high levels of human A3B by inserting a strong CAG promoter upstream of the transcription stop cassette (CAG-A3B versus R26-A3B schematics in Figure 1A; additional details in Figure S1).