A composition comprising a main species HER2 antibody that binds to domain II of HER2, and an amino acid sequence variant thereof comprising an amino-terminal leader extension is disclosed. Pharmaceutical formulations comprising the composition, and therapeutic uses for the composition are also disclosed.本發明揭示一種包含主要物種為HER2抗體的組合物,該抗體鍵結到HER2的II區域;及其胺基酸序列變異物,其包含胺基終端領導延伸(leader extension)。本發明也揭示一種包含該組合物的醫藥調配物,及該組合物的治療用途。