The present invention relates to prognostic methods which are useful in medicine, particularly cancer chemotherapy. The object of the invention to provide a method for assessing TS and/or ERCC1 expression levels in fixed or fixed and paraffin embedded tissues and prognosticate the probable resistance of a patient's tumor to treatment with 5-FU and oxaliplatin-based therapies by examination of the amount of TS and/or ERCC1 mRNA in a patient's tumor cells and comparing it to a predetermined threshold expression level for those genes. More specifically, the invention provides to oligonucleotide primer pairs ERCC1 and TS and methods comprising their use for detecting levels of ERCC1 and TS mRNA, respectively.