Metastatic breast cancer is an advanced-stage disease in which the cancer cells have spread to distant organs. To understand the patterns of metastatic colonization in a patient who presented with aggressive disease, we have collected tumor biopsies at initial diagnosis, at mastectomy necessitated by the patient's relapse, twenty-six metastatic tumors across seven organs and two normal tissue control skin biopsies via a rapid autopsy procedure within hours after the patient's death.
All biopsy samples were subjected to 60X Illumina whole genome sequencing. Our analysis revealed extensive chromosomal changes including amplifications, deletions, LOH and translocations, as well as known driver mutations in RB1, TP53, and PTEN in all tumor samples. We used the CNV and LOH data to reconstruct the phylogenetic relationships among the tumor samples. We used the somatic SNV allele frequencies in copy number-normal regions to refine these phylogenetic relationships, and to establish the evolution of the tumor at the subclonal level across different metastatic sites, with an extension of our SubcloneSeeker algorithm.
Our analysis reveals the lung as the first metastatic site. In fact, this invasion occurred before relapse at the primary site in the breast, indicating early metastatic escape. This initial invasion was followed by distinct waves of massive metastatic expansion, beginning with the abdominal organs, then the lymph nodes, brain and bones. As the initial invasion, each metastatic wave involved other distinct sites in the lungs, these sites serving as incubators where subclones further evolved prior to seeding new metastatic sites. Finally, we see clear evidence for metastatic “recolonization” where such further evolved subclones invaded already established, earlier metastatic sites.
The high number of biopsied sites in this study, 30 in all, allowed us to reconstruct the evolution of the aggressive disease in our patient with unprecedented resolution, and to identify characteristic patterns of metastatic colonization. If confirmed in additional, similarly high resolution datasets, these patterns will lead to better understanding of the metastatic process, and guide effective clinical intervention.
Citation Format: Xiaomeng Huang, Yi Qiao, Samuel W. Brady, Adam Cohen, Andrea H. Bild, Gabor T. Marth. Temporal and spatial dynamics of metastatic colonization revealed by 26 rapid-autopsy tumor biopsies from a TNBC patient [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2195.