Abstract P5-07-07: Mapping clonal evolution and tumor heterogeneity by whole exome sequencing of tissue and plasma circulating tumor DNA in metastatic breast cancer

Abstract Tumor heterogeneity in breast cancer tumors is widely recognized but evolution of the breast cancer genome is complex and not yet understood. Characterizing the evolutionary landscape of breast tumors can provide biological understanding of tumor progression and metastasis may be important for directing effective treatments. We performed copy number profiling and mutation detection based on whole exome sequencing of primary tumors, lymph node and distant metastasis as well as on plasma circulating tumor DNA from twelve metastatic breast cancer patients. Preliminary data shows diverse patterns of tumor evolution. Although linear evolution with late dissemination of metastatic cells was common, parallel evolution with early dissemination from primary tumor to distant sites was evident in some cases. Comparing tissue biopsies with plasma samples, we could detect variants mirroring primary tumor and/or metastasis, depending on the time span between the progression steps. The genomic discordance between the different stages of tumor evolution in these patients not only emphasizes the importance of molecular profiling of metastatic tissue but also the possibilities of liquid biopsies for real-time tracking of tumor clonal evolution. Citation Format: Stephanie Kavan, Torben A Kruse, Lars Andersen, Martin Larsen, Malene G Hildebrandt, Anne-Marie Bak Jylling, Marianne Ewertz, Marianne Vogsen, Mads Thomassen. Mapping clonal evolution and tumor heterogeneity by whole exome sequencing of tissue and plasma circulating tumor DNA in metastatic breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-07-07.