Forodesine hydrochloride is primarily used in the treatment of certain types of cancer, particularly T-cell acute lymphoblastic leukemia (T-ALL) and T-cell lymphoblastic lymphoma (T-LBL). It works by inhibiting the enzyme purine nucleoside phosphorylase (PNP), which is crucial for the survival of T-cells. By blocking this enzyme, the drug induces apoptosis in malignant T-cells, thereby slowing down or stopping the progression of the disease. It is often considered for patients who have not responded well to other treatments or for those with relapsed or refractory conditions. Additionally, research is ongoing to explore its potential in treating other hematologic malignancies and autoimmune disorders.