Percentage of cells expressing epithelial, NE genes (e.g., UCHL1, NCAM1, SYP, and CHGA) or SCLC lineage-specific genes (e.g., ASCL1, NEUROD1, etc.) in the CTC population and non-CTC populations. Validation of CTC identification within a patient liquid biopsy by positive expression of epithelial, NE and SCLC genes.