A drug used with other drugs to treat acute lymphoblastic leukemia (ALL). It is used in patients whose cancer has not already been treated or who cannot be treated with asparaginase. It is also being studied in the treatment of other types of cancer. PEG-asparaginase is a form of the drug asparaginase that is linked to a substance called PEG, which makes the drug stay in the body longer. Asparaginase is an enzyme that breaks down the amino acid asparagine and may block the growth of cancer cells that need asparagine to grow. It is a type of protein synthesis inhibitor. Also called Oncaspar and pegaspargase.