['Outcome and survival in anthracycline-based and cyclophosphamide/methotrexate/5-fluorouracil-based chemotherapy of invasive breast cancer are unpredictable. Insights into treatment prediction are expected from studies searching for an association between genetic polymorphisms and treatment outcome effects. A common feature of treatment with chemoreagents is therapeutically induced DNA damage. Therefore, we tested the hypothesis of a relationship between event-free survival and genotype distributions of seven polymorphic DNA repair enzymes and four cell cycle regulators.', 'This case-case comparison included 180 patients with primary invasive breast cancer diagnosed between 1986 and 2000 and subjected to adjuvant chemotherapy (anthracycline/cyclophosphamide or cyclophosphamide/methotrexate/5-fluorouracil). Ninety-two patients were reported without recurrence and 88 were reported with recurrences or dead. Median clinical follow-up was 61.7 months. Constitutional DNA isolated from archived tissues was genotyped at 19 loci by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Statistical analyses included adjusted risk estimates, Kaplan-Meier analyses, Cox proportional hazard model, and permutation testing.', 'Carriers of the XRCC1_1196_AA genotype had a reduced risk for recurrence/death (odds ratio adjusted 0.19; 95% confidence interval: 0.06-0.61), which was observed in survival analyses of all patients (P=0.003) and patients treated with chemotherapy but not radiotherapy (P=0.006). Multivariate analysis confirmed XRCC1 as a potential treatment predictor (hazard ratio 0.62; 95% confidence interval: 0.43-0.89). The result was stable upon permutation testing. No other significant associations were observed.'] Is polymorphism of the DNA repair enzyme XRCC1 associated with treatment prediction in anthracycline and cyclophosphamide/methotrexate/5-fluorouracil-based chemotherapy of patients with primary invasive breast cancer?