In addition, Tono et al. conducted a single center feasibility study of ETP therapy in 10 Japanese women with previously treated advanced HER2-positive breast cancer to investigate the safety of ETP therapy and the QOL of patients, as well as to analyze biomarkers (e.g., serum HER2 extracellular domain [sHER] levels, PIK3CA gene mutation status, and circulating peripheral regulatory T cell levels) [36]. Here, ERBB2 is linked to breast cancer.