Per E. Lønning

Mutational Signature 3 Detected from Clinical Panel Sequencing is Associated with Responses to Olaparib in Breast and Ovarian Cancers

Abstract Purpose: The identification of patients with homologous recombination deficiency (HRD) beyond BRCA1/2 mutations is an urgent task, as they may benefit from PARP inhibitors. We have previously developed a method to detect mutational signature 3 (Sig3), termed SigMA, associated with HRD from clinical panel sequencing data, that is able to reliably detect HRD from the limited sequencing data derived from gene-focused panel sequencing. Experimental Design: We apply this method to patients from two independent datasets: (i) high-grade serous ovarian cancer and triple-negative breast cancer (TNBC) from a phase Ib trial of the PARP inhibitor olaparib in combination with the PI3K inhibitor buparlisib (BKM120; NCT01623349), and (ii) TNBC patients who received neoadjuvant olaparib in the phase II PETREMAC trial (NCT02624973). Results: We find that Sig3 as detected by SigMA is positively associated with improved progression-free survival and objective responses. In addition, comparison of Sig3 detection in panel and exome-sequencing data from the same patient samples demonstrated highly concordant results and superior performance in comparison with the genomic instability score. Conclusions: Our analyses demonstrate that HRD can be detected reliably from panel-sequencing data that are obtained as part of routine clinical care, and that this approach can identify patients beyond those with germline BRCA1/2mut who might benefit from PARP inhibitors. Prospective clinical utility testing is warranted.

Constitutional BRCA1 Epimutations: A Key for Understanding Basal‐Like Breast and High‐Grade Serous Ovarian Cancer

Germline pathogenic genetic variants in the BRCA1 and BRCA2 genes are the most frequent causes of familial breast and ovarian cancer. Contrasting BRCA2, epimutations in the BRCA1 gene are frequently detected in tissue from triple‐negative breast (TNBC) and high‐grade serous ovarian cancers (HGSOC). While studies over the last decade have reported BRCA1 epimutations in white blood cells (WBC) from breast and ovarian cancer patients, the potential hazard ratio for incident TNBC and HGSOC was not formally assessed until recently.Conducting a prospective nested case‐control study on women participating in the American Women’s Health Initiative Study, we provided firm evidence that mosaic WBC BRCA1 epimutations, even at allele frequencies < 0.1%, are associated with a significantly increased risk of both incident HGSOC and TNBC > 5 years after WBC collection. In a second study assessing BRCA1 epimutations in WBC and matched tumor samples from TNBC, our results indicated such epimutations to be the underlying cause of around 20% of TNBC, far exceeding the percentage of cases carrying BRCA1 germline pathogenic genetic variants.We detected primary constitutional BRCA1 epimutations in tissues derived from all three germ layers. They occur independently of BRCA1 promoter haplotypes but are present on the same allele in all WBC within affected individuals. Moreover, epimutations are consistently found on the same allele in normal and tumor breast tissue as well as in WBC. This finding, together with BRCA1 epimutations detected in WBC from newborns, strongly indicates an early embryonic event with clonal expansion affecting all germ layers.Future work in the field must lead to an understanding of exactly when and how the BRCA1 epimutations occur and, most importantly, whether primary constitutional epimutations in genes other than BRCA1 may cause an elevated risk of other cancer types.