The present invention describes methods and probe composition for an automated FISH assay of a blood sample containing circulating tumor cells expressing the IGF-1R gene. The assay provides genetic analysis of suspect circulating tumor cells that have been identified after immunomagnetic selection and fluorescent labeling. Using unique, repeat-free probes to the IGF-1R locus and a chromosome 15 reference probe, cell lines expressing an aberrant number of IGF-1R and Chr 15 signals were detected, including one cell line with a low level of IGF-1R amplification. The ability to directly examine the genetic profile of IGF-1R on circulating tumor cells may provide an automated means for assessing disease and patient response to therapy.