Used primarily in the treatment of T-cell acute lymphoblastic leukemia (T-ALL) and T-cell lymphoblastic lymphoma, especially in patients who have not responded to or have relapsed after prior chemotherapy. It is a prodrug of ara-G, which gets phosphorylated in T-cells to an active metabolite that interferes with DNA synthesis, leading to cell death. Due to its selective toxicity toward T-cells, it is particularly effective in aggressive T-cell malignancies. Administered intravenously, it is often part of salvage therapy regimens in pediatric and adult patients.