Expression of cytokeratin 8 in lung cancer cell lines and measurement of serum cytokeratin 8 in lung cancer patients.

It has been reported that cytokeratin 8 (CK8) can be expressed in several cancers and expression of CK8 is correlated with increased invasiveness of the tumor in vitro and in vivo. In the present study, we investigated expressions of CK8 in human lung cancer cell lines. In addition, we also evaluated the clinical significance of CK8 measurements in sera of patients with lung cancer. Expression of mRNA for CK8 was semi-quantitatively evaluated by the competitive reverse transcriptase-polymerase chain reaction (competitive RT-PCR), using human lung cancer cell lines. The level of CK8 protein in culture supernatants of lung cancer cell lines and 70 sera of patients with lung cancer was measured by enzyme-linked immunosorbent assay (ELISA). Levels of serum CK8 according to clinical parameters were also examined. The level of expression of CK8 mRNA in non-small cell lung cancer (NSCLC) cell lines was significantly high compared with that of small cell lung cancer (SCLC) cell lines (P<0.05). The level of CK8 in culture supernatants in NSCLC was significantly high compared with that of SCLC. The level of serum CK8 in patients with NSCLC was significantly high compared with that of normal non-smokers and compared with that of SCLC (P<0.05). Patients with a CK8 value of 50.0 ng/ml, or higher, had a statistically significant diminished survival compared with those patients whose CK8 values were lower. In conclusion, CK8 was preferentially expressed in NSCLC. Increasing values of CK8 were significantly associated with tumor progression and decreased survival in patients with NSCLC. Therefore, CK8 in sera may become a novel tumor marker in patients with lung cancer.