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3433 CANCER SEPTEMBER 15, 2017 3 Content in this section does not reflect any official policy or medical opinion of the American Cancer Society or of the publisher unless otherwise noted. © American Cancer Society, 2017. I a recent study conducted by the Wellcome Trust Sanger Institute in Hinxton, United Kingdom, collaborators discovered that a number of breast cancers are genetically similar to rarer cases with faulty BRCA1 or BRCA2 genes.1 As a result, they estimate that up to 20% of breast cancer patients may be able to be treated with poly(adenosine diphosphateribose) polymerase (PARP) inhibitors, which previously were thought to be effective for women with inherited BRCA1 or BRCA2 mutations only. Between 1% and 5% of breast cancer cases are caused by inherited mutations in BRCA1 and BRCA2 genes, which are linked to higher risks of both breast and ovarian cancers. PARP inhibitors are designed to treat tumors with these faulty genes and are also being investigated for use against prostate cancer. In the study, researchers analyzed the breast cancer genomes of 560 patients and examined every possible mutation. They then developed a computer-based tool called HRDetect to identify patterns of mutations in the tumors that were similar to mutations in the BRCA1 and BRCA2 genes. The researchers found that many breast cancer patients had mutational signatures that were identical to those of people with faulty BRCA1 and BRCA2 genes, even though they had not inherited the mutations. The authors say the findings suggest that approximately 1 in 5 breast cancer patients could benefit from existing PARP inhibitor treatment, although clinical trials would be needed to verify that hypothesis. Researchers add that uncovering previous defects in patients’ DNA repair machinery was possible only with the sequencing of the entire genome of the cancers, and additional work is needed to determine whether there are tumors with the same mutational signatures elsewhere in the body that may respond to the drugs.