A substance being studied in the treatment of cancer that has spread to the brain. It has also been studied in the treatment of other types of cancer. Cytochlor damages the DNA in cancer cells, which may make them easier to kill with radiation therapy. It is a type of radiosensitizing agent. OR An antimetabolite analogue of cytidine with a modified sugar moiety (arabinose instead of ribose). Cytarabine is converted to the triphosphate form within the cell and then competes with cytidine for incorporation into DNA. Because the arabinose sugar sterically hinders the rotation of the molecule within DNA, DNA replication ceases, specifically during the S phase of the cell cycle. This agent also inhibits DNA polymerase, resulting in a decrease in DNA replication and repair.