Circulating Tumors Cells as a Biomarker of Radiation Benefit

Based on the findings of multiple prospective, randomized, phase 3 clinical trials showing improved local control and disease-free survival and the Early Breast Cancer Trialist's Collaborative Group (EBCTCG) meta-analysis showing overall survival benefit, adjuvant radiation therapy has become the standard of care after breast-conserving surgery (BCS) for patients with early-stage breast cancer. In addition, similar randomized clinical trial data and meta-analyses demonstrate the benefit of postmastectomy radiation therapy for women with axillary node–positive disease. Despite evidence of a benefit from radiation therapy in these unselected populations, no accepted biomarkers are available to predict the benefit from adjuvant radiation therapy for individual patients. In contrast, the development and proven utility of molecularly based gene expression signatures to guide decisions on the use of adjuvant systemic chemotherapy suggest that a risk-adapted, personalized biomarker strategy might also be feasible to predict benefit from radiation. OncotypeDx (Genomic Health), Prosigna (NanoString), MammaPrint (Agendia), EndoPredict (Myriad Genetics), Mammostrat (Clarient Diagnostic Services), and the Breast Cancer Index are examples of gene-expression signatures in early-stage breast cancer; several tests are used in clinical practice to predict the additional benefit of adding chemotherapy to adjuvant endocrine therapy. Studies from multiple groups developing gene expression signatures for a response to radiation therapy have been published, but none are ready for clinical adoption.

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