CXCR4 and small cell lung carcinoma: Combined analysis of exosomal protein expression and patients' CTCs revealed that the subgroup of SCLC patients with CXCR4 exosomal overexpression (47 out of 58), who harbored four or more CTCs with the (CK+CXCR4+JUNB−) phenotype, exhibited lower PFS [3 months (range 0.74–5.26) vs 4.99 months (range 4.01–5.97), respectively; P = 0.047, HR = 0.31 (95% CI: 0.09–1.11); Fig. 6], compared to patients that had three or less (CK+CXCR4+JUNB−) CTCs.