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Addressing drug resistance is a core challenge in cancer research, but the degree of heterogeneity in resistance mechanisms in cancer is unclear. In this study, we conducted next-generation sequencing (NGS) of circulating tumor cells (CTC) from patients with advanced cancer to assess mechanisms of resistance to targeted therapy and reveal opportunities for precision medicine. Comparison of the genomic landscapes of CTCs and tissue metastases is complicated by challenges in comprehensive CTC genomic profiling and paired tissue acquisition, particularly in patients who progress after targeted therapy. Thus, we assessed by NGS somatic mutations and copy number alterations (CNA) in archived CTCs isolated from patients with metastatic breast cancer who were enrolled in concurrent clinical trials that collected and analyzed CTCs and metastatic tissues. In 76 individual and pooled informative CTCs from 12 patients, we observed 85% concordance in at least one or more prioritized somatic mutations and CNA between paired CTCs and tissue metastases. Potentially actionable genomic alterations were identified in tissue but not CTCs, and vice versa. CTC profiling identified diverse intra- and interpatient molecular mechanisms of endocrine therapy resistance, including loss of heterozygosity in individual CTCs. For example, in one patient, we observed CTCs that were either wild type for ESR1 ( n = 5/32), harbored the known activating ESR1 p.Y537S mutation ( n = 26/32), or harbored a novel ESR1 p.A569S ( n = 1/32). ESR1 p.A569S was modestly activating in vitro , consistent with its presence as a minority circulating subclone. Our results demonstrate the feasibility and potential clinical utility of comprehensive profiling of archived fixed CTCs. Tissue and CTC genomic assessment are complementary, and precise combination therapies will likely be required for effective targeting in advanced breast cancer patients. Significance: These findings demonstrate the complementary nature of genomic profiling from paired tissue metastasis and circulating tumor cells from patients with metastatic breast cancer. Cancer Res; 78(4); 1110-22. ©2017 AACR ., (©2017 American Association for Cancer Research.)

This is an exciting time to be in cancer medicine. New technologies, such as next-generation sequencing (NGS), have increased our understanding of the molecular aberrations that define cancer. This, in turn, has led to the identification of cancer-specific molecular targets and potential drugs to confront these targets. As these new technologies move toward clinical application, a new vocabulary of "genome medicine" has been introduced to the field of oncology. Unfortunately, unclear or incorrect use of the new terminology has led to semantic misunderstandings that impair communication between the basic research and clinical practice arenas. These misunderstandings have led to assumptions regarding the clinical application of NGS and other technologies that may or may not be true. For example, some organizations that perform NGS testing on clinical samples have endorsed use of the results of such tests to direct specific therapies based on laboratory hypotheses, but without clinical testing of the hypotheses to show utility for these potential predictive claims. Here, we review some simple, and hopefully universally acceptable, definitions, concepts, and trial designs so that laboratory researchers and clinicians can move closer toward speaking the same language., (©2015 American Association for Cancer Research.)

Circulating tumor cells (CTC) are emerging as a powerful prognostic and predictive biomarker in several types of cancer, including breast, colon, and prostate. Studies of CTC in metastasis and further development of CTC as a biomarker in cancer have been limited by the inability to repetitively monitor CTC in mouse models of cancer. We have validated a method to enumerate CTC in blood samples obtained from living mice using a modified version of an in vitro diagnostic system for quantifying CTC in patients. Different routes of blood collection were tested to identify a method to reproducibly recover CTC from tumor-bearing mice without interference from contaminating normal murine epithelial cells. CTC are present in blood samples from mice bearing orthotopic xenografts of several different breast cancer cell lines and primary breast cancer cells from patient biopsies. We also show that this technology can be used for serial monitoring of CTC in mouse xenograft models of human breast cancer. These results establish a new method for studying CTC in mouse models of epithelial cancer, providing the foundation for studies of molecular regulation of CTC in cancer and CTC as biomarker for therapeutic efficacy.