Abstract CN08-02: Molecular detection and characterization of circulating tumor cells

Circulating tumor cells (CTCs) are shed from primary and metastatic tumor deposits into the bloodstream, where a small fraction may survive and ultimately give rise to distant lesions. As such, analysis of CTCs provides a noninvasive strategy to repeatedly sample tumor cells during the course of cancer progression and evolution, as well as to better understand the process of cancer metastasis. In addition, the early shedding of CTCs into the blood by localized but invasive cancers may present an opportunity for earlier detection and treatment of cancers, before metastases are established. We have previously described a microfluidic negative depletion platform, the CTC-iChip, which efficiently depletes blood specimens of normal hematopoietic cells, leaving behind untagged and unmanipulated CTCs. This technology, which is now automated, allows for enrichment of tumor cells from blood samples, without bias based on their expression of epithelial or other cell surface markers. Single-cell sequencing of CTCs captured in this way demonstrates high-quality RNA reads, enabling detailed molecular characterization, and some CTCs are viable, expanding in vitro to generate tumorigenic cell lines. In characterizing such cell lines derived from the blood of women with hormone receptor-positive breast cancer, we have identified both acquired treatment-associated mutations, as well as cell fate changes that may be of epigenetic origin. Among these, the acquisition of HER2 expression by initially HER2-negative breast cancer cells signals the emergence of a highly proliferative albeit chemotherapy-susceptible cell population, which appears to coexist and even interconvert with a less proliferative Notch1-dependent drug-resistant population. The interplay between these distinct cell populations in advanced hormone receptor-positive breast cancer and its impact on acquired drug resistance can be modeled using patient CTC-derived cultured cell lines. Finally, the intact CTCs isolated from patient blood samples using negative depletion microfluidic technologies also enable high-sensitivity, RNA-based digital PCR scoring of rare cancer cells within a blood specimen. Such highly quantitative and automatable analyses provide rapid measurements of tumor-specific burden from blood samples, before and after therapeutic intervention, and enable interrogation of intracellular signaling pathways that are targeted by drug treatment. In breast cancer, CTC-based scoring of estrogen receptor signaling pathways provides serial noninvasive monitoring of a major tumor driver, with implications for treatment selection. Taken together, technological advances in the isolation and analysis of CTCs present opportunities for cancer cell-based monitoring of breast cancer and other malignancies, in which distinct treatment options need to be molecularly targeted for individualized therapy. Citation Format: Daniel A. Haber. Molecular detection and characterization of circulating tumor cells [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr CN08-02.