The findings revealed that cancer patients receiving ICIs with lower CEA levels had significantly improved OS (HR: 1.84, p < 0.001) and PFS (HR: 1.64, p < 0.001), along with higher DCR (OR: 1.81, p = 0.001), ORR (OR: 0.53, p = 0.001), and pCR (OR: 0.58, p < 0.001) compared to those with elevated CEA levels. Here, CEACAM5 is linked to cancer.