Immunotherapy using checkpoint inhibitors has dramatically improved melanoma treatment response. However, only a subset of patients show durable remissions. Hong et al. studied circulating tumor cells (CTCs) from the blood of 49 melanoma patients to identify biomarkers that may predict therapeutic outcomes. They developed a two-part test, wherein an RNA digital PCR (polymerase chain reaction) gene signature was combined with microfluidic enrichment for CTCs. A reduced CTC score within the first 7 weeks of therapy correlated with progression-free survival and overall survival in the small cohort studied. Liquid biopsy strategies may provide a means to distinguish which patients are the best candidates for immunotherapy using checkpoint blockade.
