[67Ga]Ga-US2 showed significantly higher accumulation in the HT-29 tumor (2.98−4.63% injected dose/g) than that in the MDA-MB-231 tumor (1.64−2.58% injected dose/g) at all evaluated timepoints, indicating the selective accumulation in CA-IX high-expressing tumors. The gene discussed is CA9; the disease is neoplasm.