CPA4 and colorectal cancer: Further analysis indicated that the serum levels of CPA4 were 2480.47 ± 507.90 pg/mL in colorectal cancer without liver metastasis, 3717.89 ± 375.98 pg/mL in colorectal cancer with simultaneous liver metastasis, and 3692.12 ± 261.51 pg/mL in colorectal cancer with heterogeneous liver metastasis and the differences were significant (p < 0.05) (Figure 2A).