Comprehensive analyses of cancer genomes promise to inform prognoses and precise cancer treatments. A major barrier, however, is inaccessibility of metastatic tissue. A potential solution is to characterize circulating tumor cells (CTCs), but this requires overcoming the challenges of isolating rare cells and sequencing low-input material. Here we report an integrated process to isolate, qualify and sequence whole exomes of CTCs with high fidelity, using a census-based sequencing strategy. Power calculations suggest that mapping of >99.995% of the standard exome is possible in CTCs. We validated our process in two prostate cancer patients including one for whom we sequenced CTCs, a lymph node metastasis and nine cores of the primary tumor. Fifty-one of 73 CTC mutations (70%) were observed in matched tissue. Moreover, we identified 10 early-trunk and 56 metastatic-trunk mutations in the non-CTC tumor samples and found 90% and 73% of these, respectively, in CTC exomes. This study establishes a foundation for CTC genomics in the clinic.

Cancer is an inflammatory disease of tissue that is largely influenced by the interactions between multiple cell types, secreted factors, and signal transduction pathways. While single-cell sequencing continues to refine our understanding of the clonotypic heterogeneity within tumors, the complex interplay between genetic variations and non-genetic factors ultimately affects therapeutic outcome. Much has been learned through bulk studies of secreted factors in the tumor microenvironment, but the secretory behavior of single cells has been largely uncharacterized. Here we directly profiled the secretions of ELR+ CXC chemokines from thousands of single colorectal tumor and stromal cells, using an array of subnanoliter wells and a technique called microengraving to characterize both the rates of secretion of several factors at once and the numbers of cells secreting each chemokine. The ELR+ CXC chemokines are highly redundant, pro-angiogenic cytokines that signal via either or both of the CXCR1 and CXCR2 receptors, exerting profound impacts on tumor growth and progression. We find that human primary colorectal tumor and stromal cells exhibit polyfunctional heterogeneity in the combinations and magnitudes of secretions for these chemokines. In cell lines, we observe similar variance: phenotypes observed in bulk can be largely absent among the majority of single cells, and discordances exist between secretory states measured and gene expression for these chemokines among single cells. Together, these measures suggest secretory states among tumor cells are complex and can evolve dynamically. Most importantly, this study reveals new insight into the intratumoral phenotypic heterogeneity of human primary tumors.

Comprehensive analysis of cancer genomes in clinical settings holds the promise to inform prognoses and guide the deployment of precise cancer treatments. A major barrier, however, is the inaccessibility of adequate metastatic tissue for accurate genomic analysis. The recognition that circulating tumor cells (CTCs) are present in many advanced cancer patients suggests an exciting opportunity to overcome this challenge. For instance, if CTCs could be comprehensively sequenced, it would be possible to obtain an orthogonal sample of the tumor burden_including subsets of transiting cells bound for metastatic colonization_potentially yielding new insights to complement the static sampling of resected or biopsied lesions. We report an integrated process to isolate, qualify, and sequence whole exomes of CTCs with high fidelity, using a census-based sequencing strategy. We isolated CTCs by magnetic bead purification (Illumina MagSweeper) from the blood of patients with prostate cancer, and integrated a nanowell platform to automatically image and recover candidate single CTCs. We then developed a strategy to qualify individual CTC-derived libraries for DNA sequencing after whole genome amplification, and established an analytical framework for accurate calling of mutations using census-based sequencing and MuTect. Whole exome sequencing was performed on 20 single CTCs, obtained from a patient with advanced prostate cancer. We validated our sequencing process by comparing CTC-derived mutations to mutations found in a lymph node metastasis and nine separate cores of the primary tumor. 51 of 73 CTC mutations (70%) were observed in the metastasis or the primary tumor. Moreover, we identified 9 early trunk mutations and 56 metastatic trunk mutations in the non-CTC tumor samples and found 100% and 73% of these, respectively, in CTC exomes. Our work demonstrates the feasibility of CTC sequencing and the ability to confidently call somatic mutations. CTCs may therefore represent a non-invasive window into the mutational landscape of metastatic cancer, and may have utility for genomics in clinical practice. Citation Format: Viktor A. Adalsteinsson, Jens G. Lohr, Kristian Cibulskis, Atish D. Choudhury, Mara Rosenberg, Peter Cruz-Gordillo, Joshua Francis, ChengZhong Zhang, Alexander K. Shalek, Rahul Satija, John T. Trombetta, Diana Lu, Naren Tallapragada, Narmin T. Tahirova, Sora Kim, Brendan Blumenstiel, Carrie Sougnez, Daniel Auclair, Eliezer M. Van Allen, Mari Nakabayashi, Rosina T. Lis, Gwo-Shu M. Lee, Tiantian Li, Matthew S. Chabot, Mary-Ellen Taplin, Thomas E. Clancy, Massimo Loda, Aviv Regev, Matthew Meyerson, William C. Hahn, Philip W. Kantoff, Todd R. Golub, Gad Getz, Jesse S. Boehm, J Christopher Love. Whole exome sequencing of CTCs as a window into metastatic cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 993. doi:10.1158/1538-7445.AM2014-993