Maarten Vermeer, MD, PhD, Leiden University Medical Center, Leiden, Netherlands, outlines unmet needs in cutaneous T-cell lymphoma, highlighting challenges around the quantification of tumor cells in CTCL, due to heterogeneity in cell surface markers both between and within individual patients. Dr Vermeer also comments on how improving tumor cell quantification could be used to enhance therapeutic approaches such as extracorporeal photopheresis and mogamulizumab. This interview took place at the EORTC Cutaneous Lymphoma Group 20-21 meeting in Marseille.