Maarten Vermeer, MD, PhD, Leiden University Medical Center, Leiden, Netherlands, gives an overview of the multimarker approach to biomarker research and its role in the quantification of circulating tumor cells (CTCs) for diagnosis and treatment-response analysis in cutaneous T-cell lymphoma (CTCL). This interview took place at the EORTC Cutaneous Lymphoma Group 20-21 meeting in Marseille.