Multicenter study validates PITX2 DNA methylation for risk prediction in tamoxifen-treated, node-negative breast cancer using paraffin-embedded tumor tissue

Abstract

505 Background: In hormone receptor positive, node-negative breast cancer, many patients receive chemo-endocrine therapy although endocrine therapy alone would have been sufficient in view of their excellent prognosis. In a microarray study, we recently reported that PITX2 methylation correlates strongly with the risk of recurrence after adjuvant tamoxifen. Here, we present results from a large multicenter study initiated to validate PITX2 methylation as an outcome predictor for adjuvant tamoxifen using paraffin-embedded tumor tissue. Methods: A real-time PCR assay was developed to test PITX2 methylation in paraffin-embedded tissue. Matched frozen and embedded samples (n=89) were analyzed to ensure comparability of Results: Then, we analyzed paraffin-embedded tumors of 422 node-negative patients from 9 clinical centers treated with tamoxifen alone; none of the patients had been included in the prior studies. Results: Results from the matched pairs indicated that the assay works well on paraffin-embedded material (correlation coefficient = 0.81). In the independent cohort, PITX2 methylation was strongly correlated with outcome (Cox proportional hazard model, p=0.025). In the group with low PITX2 methylation (45% of the cohort), 98% of the patients were metastasis-free after 10 years, compared to only 85% in the group with high PITX2 methylation. In a multivariate model, PITX2 methylation added significant information to conventional factors such as tumor size, grade, and age. Conclusions: This study validates PITX2 methylation as outcome predictor after adjuvant tamoxifen. Together with our previous studies, we have now analyzed over 750 patients, using two different Methods: In all studies, PITX2 methylation was consistently associated with poor outcome. Furthermore, we have now shown that PITX2 methylation can be reliably measured in paraffin-embedded tissue. The results provide substantial evidence that PITX2 DNA methylation is suitable for routine clinical use in order to predict outcome in node-negative, tamoxifen-treated patients, and to identify low-risk patients who can be spared the burden of additional cytotoxic therapy.