SAN ANTONIO – Patients with estrogen receptor–positive breast cancers who had up-regulation of the APOBEC3B enzyme – a DNA-mutating enzyme – had a shorter time to progression on tamoxifen. In addition, suppressing levels of the enzyme in a preclinical model reduced tamoxifen resistance. In an interview, Reuben Harris, Ph.D., professor in the department of biochemistry, molecular biology, and biophysics at the University of Minnesota, Minneapolis, discussed the study’s findings and what they mean for the conduct of clinical trials and for future research.