Abstract LB-353: Mutational profile of metastatic breast cancers using whole-exome sequencing: a retrospective analysis of 216 samples from SAFIR01 / 02 / SHIVA / MOSCATO trials
Authors: Kamal Maud , Lefebvre Celine , Bachelot Thomas , Filleron Thomas , Pedrero Marion , Campone Mario , Soria Jean-Charles , Massard Christophe , Levy Christelle , Arnedos Monica , Garrabey Julie , Boursin Yannick , Deloger Marc , Fu Yu , Commo Frederic , Scott Veronique , Lacroix Ludovic , Martin Emmanuel , Dieras Veronique , Goncalves Anthony , Ferrero Jean-Marc , Romieu Gilles , Vanlemmens Laurence , Mouret-Reynier Marie-Ange , Thery Jean-christophe , Kerbrat Pierre , Guiu Severine , Dalenc Florence , Clapisson Gilles , Bonnefoi Hervé , Jimenez Martha , Le Tourneau Christophe , Andre Fabrice 
Published: July 2016

Abstract
Background: Major advances have been achieved in the understanding of breast cancer biology using high throughput technologies at the DNA and RNA levels. Most of these advances were made in early breast cancers (eBC) which are cured in about 80% of the cases. Nevertheless, little is known about metastatic breast cancers (mBC) which remain lethal in most of the cases.
Methods: Whole-exome sequencing was performed on 216 tumour-normal pairs from mBC patients who underwent a biopsy in the context of the SAFIR01/SAFIR02/SHIVA or MOSCATO prospective trials. TCGA dataset (n = 772) was used to assess frequency of mutations in eBC.
Findings: Twelve genes (TP53, PIK3CA, GATA3, ESR1, MAP3K1, CDH1, AKT1, MAP2K4, RB1, PTEN, CBFB, CDKN2A) were identified as drivers using MutSig algorithm (FDR&lt;0.1). Eight genes (ESR1, FSIP2, FRAS1, OSBPL3, EDC4, PALB2, IGFN1, AGRN) were more frequently mutated in mBC as compared to eBC (TCGA, FDR&lt;0.01). HR+/Her2- mBC presented a high prevalence (6.3%) of mutations on genes located on mTOR pathway (TSC1, TSC2) as compared to HR+/Her2- eBC (0.7%, p = 0.0004). A subset of HR+/Her2- mBC (n = 17, 12%) presented a high mutational load (&gt;150 non-synonymous mutations). This subset was observed in 2% of early breast cancers (TCGA, p = 7.1e?06). The prevalence of this subset increased with the time from diagnosis of metastasis to biopsy. Highly mutated HR+/Her2- mBC (n = 17) presented higher rate of PIK3CA mutations (n = 12, 70%), high number of neoantigens, an APOBEC mutational signature and a poor outcome (multivariate analysis, HR = 4.68, 95%CI: 1.8-12.1, p = 0.001).
Interpretation: Whole exome sequencing of metastatic breast cancers identifies a subset of HR+/Her2- mBC who present a high mutational load. RB1, PALB2 and TSC1/2 mutations were found enriched in either mBC or HR+ mBC.
Fundings: Breast Cancer Research Foundation, Fondation ARC, Fondation Lombard-Odier “Philanthropia”, Odyssea, Operation Parrains Chercheurs, Dassault Foundation, French NCI: INCa-DGOS-INSERM 6043
Citation Format: Maud Kamal, Celine Lefebvre, Thomas Bachelot, Thomas Filleron, Marion Pedrero, Mario Campone, Jean-Charles Soria, Christophe Massard, Christelle Levy, Monica Arnedos, Julie Garrabey, Yannick Boursin, Marc Deloger, Yu Fu, Frederic Commo, Veronique Scott, Ludovic Lacroix, Emmanuel Martin, Veronique Dieras, Anthony Goncalves, Jean-Marc Ferrero, Gilles Romieu, Laurence Vanlemmens, Marie-Ange Mouret-Reynier, Jean-christophe Thery, Pierre Kerbrat, Severine Guiu, Florence Dalenc, Gilles Clapisson, Hervé Bonnefoi, Martha Jimenez, Christophe Le Tourneau, Fabrice Andre. Mutational profile of metastatic breast cancers using whole-exome sequencing: a retrospective analysis of 216 samples from SAFIR01 / 02 / SHIVA / MOSCATO trials. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-353.