The prognosis of patients with metastatic melanoma has improved significantly with targeted therapeutic agents and immunotherapies. Detection of early melanoma recurrence after treatment will be beneficial to switch patients who fail on one therapy to different modalities. Circulating tumor cells (CTCs) are cancer cells released by a tumor into the peripheral blood. These cells hold potential as prognostic, predictive, and pharmacodynamic biomarkers for treatment. In this issue, Khoja et al. report that melanoma CTCs can be detected using Melcam and high molecular weight melanoma-associated antibody. They found that in 101 stage IV melanoma patients, CTC numbers ranged between 0 and 36/7.5 ml blood; 26% of the patients had ≥ 2 CTCs at baseline. The CTC number (≥ 2 CTCs) at baseline was significantly prognostic for median overall survival (OS) in univariate and multivariate analysis. Patients receiving treatment where CTC numbers remained ≥ 2 CTCs during their treatment had shorter median OS than those who maintained <2 CTCs (7 vs. 10 months, hazard ratio 0.34, 95% confidence interval 0.14-0.81, log-rank test P=0.015). The implications of this work are substantial in counseling patients about their prognosis and in helping to assess responses to systemic therapies.