Objective:To evaluate the real-time fluorescent quantitative-polymerase chain reaction approach(fqRT-PCR) of cytokeratin 19(CK19)targets for its feasibility to estimate the number of circulating tumor cells(CTCs)in the patients with lung carcinoma during radiotherapy and to correlate our observation to clinical findings.Methods:Samples of 5ml peripheral blood were taken from each lung cancer patients(n=30)both before and after the radiotherapy course.Meanwhile tumour size was determined by chest X-ray or computed tomography.The blood samples were subjected to real time RT-PCR assay.All patients with lung cancer were treated with primary definitive and mediastinal radiotherapy.Results:Compared to with that before the-treatment

the value of CK19 mRNA in PB after therapy decreased dramaticall(y5.093 2±1.062 8 vs 4.249 3 ±0.832 3

t=3.192

P=0.007).The change of CK19 mRNA level before and after radiotherapy was closely related to the typ(esquamous cell cancer/adenocarcinoma vs.small cell cancer

0.538 9±0.903 0 vs 1.682 6±0.946 7

t=2.146 5

P=0.051).Meanwhile

there was a close link between the grade(Well/Mod vs Poor)and the change of CK19 mRNA(0.502 4 vs 1.527 1

t=2.017

P=0.065).The change of CK19 mRNA level in peripheral blood(PB)was related to variation of tumour burden during radiotherapy(r=0.057 5

P=0.025).Of the 30 cases studied

24 cases were positive before radiotherapy (24/30

80%).The positive rate was 53%(16/30)after radiotherapy

meaning that 8 cases were converted intonegative after radiotherapy. Conclusion:The disseminated cancer cells cannot be completely eradicated by radiotherapy

suggesting further more systemic adjuvant treatment should be conducted.Early assessment of the therapeutic response might be possible by serial quantitative of CTCs.Detection of tumour cells disseminated in peripheral blood can provide clinically important data that are of value for tumour staging and possibly for prognostication.