This is a multicenter, open-label, single-arm study of E7777 in participants with recurrent or persistent Cutaneous T-Cell Lymphoma (CTCL). The study will consist of an initial lead-in phase (in which a dose of E7777 will be selected), followed by the Main Study. Participants will move through three phases while on study: Pretreatment Phase, Treatment Phase, and Extension Phase and a Follow-up Period.