Trastuzumab-based chemotherapy has demonstrated clinical benefits in the treatment of HER2+ breast cancer. There is a percentage of patients who do not respond to therapy and have a poorer prognosis than those who respond. To better understand the mechanisms behind trastuzumab resistance, researchers in China studied the role of transcription elongation factor A protein-like 9 (TCEAL9) in resistance to trastuzumab-based chemotherapy in HER+ breast cancer.