Circulating tumor cells as emerging tumor biomarkers in lung cancer

Enumeration of circulating tumor cells (CTCs) has been shown to correlate with poor progression free survival (PFS) and overall survival (OS) in breast, colorectal, and prostate cancers. In lung cancer, there is a large need for more and multiple tumor biomarkers that will allow monitoring of patient progress over the course of therapy. Studies have suggested that the primary treatment for lung cancer, surgery, can lead to an increase of CTCs (1,2). This may lead to a different sort of residual disease even in successful cases of full tumor resection. In CTC studies involving lung cancer, CTC enumeration as a method to monitor patient progress has not been as convincing because CTCs were not found in many study patients, and those patients with CTCs had numbers far lower than other cancer types (3-5). In order for CTCs to become a useful biomarker for lung cancer, there is a need to look beyond enumeration and an understanding of the molecular characteristics of the CTCs and their similarities and differences from their tumor of origin. The ability to quickly define a patient’s disease based on molecular signatures as well as identify whether a patient is responding to therapy is potentially a powerful clinical tool for a fast-acting disease.