TOP2A and cancer: Results from the HR subgroups showed that HR− patients received an OS benefit from H regardless of whether an anthracycline- or non-anthracycline-containing regimen was administered, whereas HR+ patients received OS benefit from an anthracycline-containing regimen with H. This difference may be due to coamplification of topoisomerase II alpha (TOP2A), which occurs in about a third of HER2+ cancers, and results in increased anthracycline sensitivity, longer progression-free survival, and improved OS [43–45].