The present disclosure provides a method for of determining the level of circulating tumor cells (CTCs) in a sample having blood cells from a patient comprising obtaining a test sample from a human subject; enriching circulating tumor cells (CTC); hybridizing the enriched cells in the sample with labeled nucleic acid probes that hybridize to regions of chromosomal DNA; evaluating the signal pattern for the selected cells by detecting fluorescence in situ hybridization from cells; detecting CTCs based on the pattern of hybridization to the labeled nucleic acid probes to said selected cells; and identifying the subject at risk for the development of lung cancer when the number of CTC per sample is above a predetermined cutoff value.--