Used primarily in the treatment of T-cell acute lymphoblastic leukemia (T-ALL) and T-cell lymphoblastic lymphoma (T-LBL), particularly in patients who have not responded to or have relapsed after standard chemotherapy regimens. It works by interfering with the DNA synthesis of cancer cells, leading to their destruction. Administered intravenously, it is often considered when other treatment options have failed. Careful monitoring is required due to potential side effects, including neurological toxicity.