Enzon Pharmaceuticals' ( ENZN) drug Oncaspar received expanded approval from the Food and Drug Administration to treat the rare blood cancer acute lymphoblastic leukemia. The approval was based on safety data from trials involving 2,000 children with the disease. Oncaspar would be used in combination with other chemotherapy drugs in treating the condition. The drug works by depleting leukemia cells of a certain amino acid necessary for their survival. Oncaspar was initially FDA-approved in 1994 to treat specific ALL patients who were overly sensitive to an enzyme known as L-asparaginase. The new labeling would allow Enzon to market the drug as a treatment for every patient with ALL, effectively doubling the market for the drug. While ALL is expected to affect no more than 4,000 people in 2006, according to the American Cancer Society, it's the most common form of cancer in children, representing 23% of cancer diagnoses in patients younger than 15 years old. Without treatment, most patients don't survive more than five months. Enzon's shares rose 28 cents, or 3.6%, to $7.98 Tuesday.