Studies of various malignancies show the ability to identify circulating tumor cells (CTCs) even in early stage cancer. The number of CTCs correlates with disease outcome. Dynamics of CTCs after CT or bronchoscopy guided biopsy has not been evaluated so far. In the metastatic setting, the number of CTCs correlates to tumor response to chemotherapy in both small and non-small lung cancer (SCLC and NSCLC, respectively).