The present invention provides antisense oligonucleotides useful for identifying drug targets for cancer therapies and for enhancing current cancer therapies. The oligonucleotides of the invention are complementary to thymidylate synthase mRNA and affect expression of at least one other gene. For the enhancement of cancer therapies, such antisense oligonucleotides can be used in conjunction with standard chemotherapeutic agents in order to target thymidylate synthase, as well as other appropriate targets. The antisense oligonucleotides and the methods of the invention constitute improved antisense therapies with application to a variety of cancers.