Although LunX has been previously reported to be the most sensitive marker among the five genes LunX, muc1, KS1/4, CEA and CK19, for detecting circulating NSCLC cells by real-time RT-PCR in a study distinguishing patients with NSCLC from healthy volunteers, the specificity of LunX for lung cancer cells has not been tested [13]. The gene discussed is CEACAM5; the disease is non-small cell lung carcinoma.