Reports which used serum to detect the expression of CK18 predicted a poor outcome of breast cancer (HR = 1.24, 95%CI: 1.11–1.38, P<0.0001), while studies which used tissue as specimen indicated a reverse result (HR = 0.71, 95%CI: 0.60–0.84, P<0.00001). Here, KRT18 is linked to breast carcinoma.