Nelarabine (Atriance®) is recommended for restricted use within NHS Wales for the treatment of patients with T-cell acute lymphoblastic leukaemia (T-ALL) and T-cell lymphoblastic lymphoma (T-LBL) whose disease has not responded to, or has relapsed, following treatment with at least two chemotherapy regimens. Treatment should be restricted to patients in whom there is an intention to proceed to allogeneic stem cell transplantation, as it is not cost effective when used for palliation. Nelarabine (Atriance®) is not suitable for shared care within NHS Wales.