For the initial quantification of target expression at baseline and after several cycles of immunotherapy (anti-programmed cell death protein 1 (αPD-1)/anti-cytotoxic T-lymphocyte-associated protein 4 (αCTLA-4)) in a MC38 syngeneic colon cancer model via CXCR3-targeted PET, we used a commercially available anti-mouse CXCR3 antibody (α-CXCR3). The gene discussed is PDCD1; the disease is malignant colon neoplasm.