(ChemotherapyAdvisor) – A newly developed molecular signature predicts whether breast cancer patients will be sensitive to radiotherapy, according to an international team of researchers. This conclusion is based on a study entitled “Validation of a Radiosensitivity Molecular Signature in Breast Cancer,” which was published online in Clinical Cancer Research.

The design of this study is based on the prior development of a radiosensitivity molecular signature (RSI), which uses a specific set of breast cancer-associated genes to measure the sensitivity of 2 populations of breast cancer patients to radiotherapy. In this study, the investigators evaluated the same RSI using 2 new populations of breast cancer patients at 2 different medical centers: the Karolinska University Hospital (n=159) and Erasmus Medical Center (n=344).

Using the RSI as an outcome measure, the investigators found that “patients predicted to be radiosensitive (RS) had an improved 5-year relapse-free survival when compared with radioresistant (RR) patients (95% vs. 75%, P = 0.0212).” The investigators also found that the RSI was specific to treatment with radiotherapy as no difference in RSI was found between RS and RS patients treated without radiotherapy (71% vs. 77%, P = 0.6744).

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“Similarly, in the Erasmus dataset, radiotherapy-treated RS patients had an improved 5-year distant-metastasis-free survival over RR patients (77% vs. 64%, P = 0.0409), but no difference was observed in patients treated without radiotherapy (P = 0.9425),” the investigators wrote.

The most important observation in this study was that this RSI can predict the outcome of radiotherapy for estrogen receptor-positive breast cancer patients (HR=2.64, P = 0.0085), allowing further personalization of therapy for this population.