AFP and rectal cancer: The plasma SIRT1 level of rectal cancer patients was negatively correlated with CEA (r = −0.250, p = 0.043), CA199 (r = −0.365, p = 0.003); the variables CA125, CA724, SCC, AFP, AFU, ALT, and AST did not exhibit a statistically significant connection (p > 0.05) with each other, as indicated in Table 6.