CA9 and neoplasm: The reason probably is that targeted nanobubbles carrying CAIX polypeptides actively aggregated in CAIX-positive tumor tissues, so the number of targeted nanobubbles in the cross-sections of CAIX-positive transplanted tumor tissues was significantly more than others, including the number of blank nanobubbles in CAIX-positive transplanted tumor tissues and the number of targeted nanobubbles in CAIX-negative transplanted tumor tissues.