TOP2A gene amplification may define a subset of HER2-amplified breast cancers that are responsible for the markedly improved chemosensitivity seen in HER2-positive breast cancer.
In 31% of HER2+ tumors the amplicon extended to TOP2A, defining a subgroup of HER2+ breast cancer associated with estrogen receptor-positive status and with a trend of better survival than HER2+ breast cancers with deleted (18%) or neutral TOP2A (51%).