High-plex immunofluorescence imaging and traditional histology of the same tissue section for discovering image-based biomarkers

Precision medicine is critically dependent on better methods for diagnosing and staging disease and predicting drug response. Histopathology using hematoxylin and eosin (H&E)-stained tissue (not genomics) remains the primary diagnostic method in cancer. Recently developed highly multiplexed tissue imaging methods promise to enhance research studies and clinical practice with precise, spatially resolved single-cell data. Here, we describe the 'Orion' platform for collecting H&E and high-plex immunofluorescence images from the same cells in a whole-slide format suitable for diagnosis. Using a retrospective cohort of 74 colorectal cancer resections, we show that immunofluorescence and H&E images provide human experts and machine learning algorithms with complementary information that can be used to generate interpretable, multiplexed image-based models predictive of progression-free survival. Combining models of immune infiltration and tumor-intrinsic features achieves a 10- to 20-fold discrimination between rapid and slow (or no) progression, demonstrating the ability of multimodal tissue imaging to generate high-performance biomarkers.

56 Quantitative evaluation of the tissue micro-environment by high-resolution 17-plex immunofluorescence reveals distinct cell populations

Background

Inflammatory tumor micro-environments contain cells of various types and sub-types. The composition and spatial location of the cell populations reflects the host reaction to the inflammatory stimulus and increasingly is understood to influence responsiveness to tumor immunotherapies. Multiplexed imaging technologies allow identification of cell types and states within the spatial context of tissue architecture. We present here a prototype workflow that combines rapid high-resolution, whole-slide highly multiplexed immunofluorescence imaging with advanced image analysis tools for 1) segmenting tissues, cells, and quantifying cellular phenotypes based on multiple markers and 2) determining regional densities and proximity between cells. We apply the workflow to comparative assessment of three lymphoid tissues: tonsil (follicular hyperplasia); lymph node (quiescence); lymphoma (architectural effacement).

Methods

Formalin-fixed, paraffin-embedded 5 micron sections of tonsil, lymph node and chronic lymphocytic leukemia/small lymphocytic lymphoma were deparaffinized, subjected to alkaline pH epitope retrieval, and then manually stained with a 17-plex panel including CD45 (leukocytes); CD20 (B cells); CD3d, CD4, CD8 (T cells); FOXP3 (T reg cells); CD68, CD163 (macrophages); CD45RO (activated cells); PD-L1, PD-1 (checkpoint markers); CD31 (vascular and lymphatic endothelial cells); cytokeratin, E-cadherin (epithelial cells); PCNA, Ki-67 (proliferating cells); and a nuclear dye. Stained slides were coverslipped and imaged on the Orion Instrument (RareCyte) generating .ome tiff image files. The HighPlex FL module of the HALO image analysis platform from Indica Labs with embedded HALO AI performed nuclear and cell segmentation, nuclear phenotyping, and user-defined thresholds were applied to each of the biomarkers to define positivity for the appropriate subcellular localization (nuclear, cytoplasmic, and/or membrane) for phenotypic analysis. H & E images from either the same or serial sections were integrated with the multiplex images using the HALO Serial Stain module.

Results

Regional masks that were defined by predominance of B-cells (CD20) or T-cells (CD3d) matched known lymphoid micro-anatomy of follicles and inter-follicular cortex respectively. Within the regions, populations and sub-populations of B-cells, T-cells, macrophages and vessels were measured, and their densities calculated and compared between tissues. Rare cell types of potential importance in immuno-oncology were investigated. The results demonstrate differences between the tissues at a phenotypic level that correspond to the morphologic differences seen by light microscopy.

Conclusions

Orion imaging combined with HALO image analysis provides a powerful and intuitive workflow for visualization and quantification of distinct microenvironment populations for use in translational and clinical research.

Abstract 5384: Analytic validation of an assay to detect androgen receptor splice variant ARv7 protein expression on circulating tumor cells from prostate cancer patients

Circulating tumor cells (CTCs) can provide information on drug target expression, response to therapy, and disease prognosis from a non-invasive blood draw. Currently, investigating biomarkers on CTCs is difficult due to challenges of developing multiplexed assays that also identify rare cells. Presence of the androgen receptor splice variant ARv7 in prostate cancer cells is associated with resistance to second generation anti-androgen therapies. We report here the analytical validation of an immunofluorescence assay for characterization of ARv7 protein expression on CTCs using the RareCyte platform - an end-to-end platform that combines CTC sample preparation, multiparameter fluorescence staining, digital imaging, and single cell retrieval. Blood samples spiked with positive and negative cell lines for ARv7 expression were processed using the AccuCyte Sample Preparation System. Slides were auto-stained by immunofluorescence with the RarePlex ARv7 CTC Panel Kit comprised of a three-channel CTC detection base plus an ARv7 biomarker channel. The detection base consists of a nuclear dye, anti-CD45 antibody to exclude white blood cells, and cocktailed antibodies to cytokeratin (CK) and epithelial cell adhesion molecule (EpCAM). Stained slides were imaged with the CyteFinder Instrument. CTCs were identified using machine learning-based algorithms and confirmed by user review. Mean fluorescence intensity (MFI) measurements were used as a metric for ARv7 expression on confirmed CTCs. Analytic validation studies of the AR-V7 CTC assay were performed using 22RV1 (high), LNCaP (low), and BT-474 (negative) cell lines. Performance characteristics tested for ARv7 included accuracy, sensitivity, specificity, repeatability, and inter-stainer run coefficient of variation. Performance metrics for CTC recovery were calculated on spike-in and clinical samples. For recovery calculations, the number of CTCs found with the ARv7 assay was compared to the number of CTCs found with the CTC detection base assay. An ARv7 MFI threshold that segregated negative and positive cell lines was statistically defined. This threshold identified 80% of 22RV1 cells as positive for ARv7, 97% of BT-474 cells as negative, with an overall accuracy of 90%. When the assay was applied to clinical prostate cancer samples, staining with proper nuclear localization was observed. CTC recovery was at least as high with the ARv7 assay as with the base CTC detection assay.

Citation Format: Daniel Campton, Edward Lo, Lillian Costandy, Brady Gardner, Ryan Houston, Jeffery L. Werbin, Kyla Teplitz, Daniel E. Sabath, Alisa C. Clein, Celestia S. Higano, Tanisha M. Mojica, Kristin Province, Eric P. Kaldjian, Arturo B. Ramirez, Tad George. Analytic validation of an assay to detect androgen receptor splice variant ARv7 protein expression on circulating tumor cells from prostate cancer patients [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5384.

Abstract 6442: Investigation of custom biomarkers on circulating tumor cells from clinical samples using RarePlex® Developer Kits

Enumeration and phenotypic profiling of circulating tumor cells (CTCs) can give important information about tumor progression, presence of therapeutic targets, and metastatic potential. New and informative cancer-specific biomarkers are being discovered at a rapid pace, so there is a strong need for tools that enable investigator driven assays to best study and utilize these biomarkers. Through the RareCyte platform, we provide sensitive and specific assays that are optimized and validated for CTC enumeration and biomarker expression. RarePlex Developer Kits enable the addition of user-selected antibodies against biomarkers of interest to a CTC detection assay. Here we demonstrate the application of RarePlex Developer Kits to study the presence of a variety of cancer related biomarkers. Using the Developer strategy, we present results for several biomarkers, including HER2, ER, PR, EGFR, Ki67, AR, ARv7, PDL1, and PSMA. We also characterized clinical samples from prostate (AR and ARv7) and breast (HER2 and ER) cancer patients. The biomarkers demonstrated proper localization on or within model CTC control cells when using default antigen retrieval and fixation conditions. For each biomarker, fluorescence intensity cut-offs that segregated negative and positive cell lines were statistically defined to maximize classification accuracy. For clinical samples, breast and prostate cancer sample staining showed expected localization based on available clinical information. In conclusion, RarePlex Developer Kits provide a flexible tool for custom CTC assay development that enables researchers to develop assays in their own lab for characterization of phenotypic heterogeneity.

Citation Format: Edward Lo, Daniel Campton, Arturo Ramirez, Lillian Costandy, Brady Gardner, Ryan Houston, Heather Itamoto, Jeffery L. Werbin, VK Gadi, Tanisha Mojica, Alisa Clein, Celestia Higano, Daniel E. Sabath, Eric P. Kaldjian, Tad George. Investigation of custom biomarkers on circulating tumor cells from clinical samples using RarePlex® Developer Kits [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6442.

Abstract 5368: A multiparameter assay for HER2 protein detection on circulating tumor cells in non-small cell lung cancer

Lung cancer biopsy can be difficult to perform successfully; it has a 30% adverse event risk and often provides insufficient material to test. Therefore, a liquid biopsy method to analyze the tumor is advantageous. Analysis of circulating tumor cells (CTCs) by multiparameter immunofluorescence (IF) microscopy allows non-invasive characterization of cancer cell biomarker expression. HER2 is a well-known therapeutic target in breast cancer and studies have shown that HER2 status on CTCs may provide prognostic information about response to anti-HER2 therapies. Less is understood about its frequency and clinical importance in non-small cell lung cancer (NSCLC). The RareCyte platform is uniquely suited for CTC identification and phenotypic characterization with a sensitive, accurate, simple and repeatable workflow from blood collection to CTC characterization and single-cell isolation. We developed an assay for detecting HER2 expression on lung CTCs using the RareCyte platform and validated the assay on model CTC spike-in samples with high (BT-474), medium (MDA-MB-453), low (H1650 and OVCAR-3) and absent (MDA-MB-468) HER2 protein levels. Blood was processed to slides using the AccuCyte Sample Preparation System and stained with anti-HER2 together with the RarePlex Kit for CTC identification (nuclear dye, anti-CD45 to exclude WBC, and anti-cytokeratin/EpCAM for CTCs). The spike-in samples showed the expected trend in per-cell HER2 mean fluorescence intensity values. The percentage of HER2-positive cells was > 90% for the HER2-high, medium and low cell lines, and < 5% for the HER2-negative cell line. The assay was applied to 10 advanced stage (III or IV) post-treatment NSCLC patient samples. At least 1 CTC was found in 6 samples (range 0-2043) and HER2 expression was confirmed in 5 out of the 6 samples, indicating this assay is useful for characterizing HER2 expression in CTCs in NSCLC.

Citation Format: Edward Lo, Daniel Campton, Lillian Costandy, Heather Itamoto, Ryan Huston, Braden Gardner, Steve Reese, Arturo Ramirez, Eric P. Kaldjian, Tad George, I-Ming Wang, Steven Pirie-Shepherd. A multiparameter assay for HER2 protein detection on circulating tumor cells in non-small cell lung cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5368.

Abstract P3-01-11: A novel six-parameter assay for comprehensive phenotyping of circulating tumor cells

Background. The presence and number of circulating tumor cells (CTCs) are prognostic for breast cancer treatment outcome. Direct imaging assays traditionally employ four markers to identify canonical epithelial CTCs: nucleus, exclusion (CD45), and inclusion (EpCAM and cytokeratin). There is intense interest in the ability to phenotype CTCs in order to provide a noninvasive means by which to predict treatment benefit from endocrine therapy and/or HER2-directed therapy in breast cancer. To address this, a 6-parameter assay for detection of ER and HER2 expression on CTCs was developed. We applied this assay to four well characterized breast cancer cell lines representative of various ER and HER2 phenotypes. Methods. BT474, MCF-7, SKBR3, or MDA-MB-231 cells were spiked into peripheral blood from healthy donors and processed using the AccuCyte® sample preparation system; nucleated cells, including CTCs, are captured onto glass slides (8 slides per 7.5 mL blood sample) for subsequent immunofluorescent staining. Slides were stained using the combined epithelial marker and ER/HER2 CTC assay and then analyzed with the CyteFinder® imaging system. CTCs were identified as nucleated cells with positive EpCAM and/or cytokeratin staining, and negative CD45 staining. ER and HER2 expression were assessed as present or absent. Results. All cell lines expressed both cytokeratin and EpCAM, except for MDA-MB-231 which was EpCAM-negative. The ER / HER2 expression patterns observed were consistent with reported phenotype: BT474 (+/+), MCF-7 (+/–), SKBR3 (–/+), and MDA-MB-231 (–/–). Conclusions. Identification of epithelial CTCs and phenotypic characterization of ER and HER2 status are feasible in a combined assay applied to a single blood sample. This approach has implications for efficiency and cost effectiveness, which are of particular importance given the interest in longitudinal testing. Assay evaluation is currently underway using blood samples from breast cancer patients with known receptor status, treatment history, and clinical outcomes. Results will be available for presentation at the meeting.

Citation Format: Liu MC, Sun Y, Ramirez A, Campton D, George T, Haselkorn KE, Clein A, Gadi V, Sabath D, Kaldjian E. A novel six-parameter assay for comprehensive phenotyping of circulating tumor cells [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P3-01-11.

Abstract 5230: Development of a multi-parameter immunofluorescence assay for simultaneous detection of androgen receptor and androgen receptor variant 7 in prostate cancer circulating tumor cells

Background. Androgen receptor (AR) signaling is the primary driver of prostate cancer. Expression of the AR splice variant AR-V7, is predictive of resistance to anti-androgen therapies enzalutimide and abiratirone. There is great interest to non-invasively identify circulating tumor cells (CTCs) and investigate their expression of AR and AR-V7 and monitor them over time. RareCyte has developed a platform for automated visual identification of CTCs by immunofluorescence (IF) that allows up to 6-parameter assessment. We have developed a set of prototype assays using tyramide amplification to detect AR and AR-V7 individually and in combination with prostate membrane-specific antigen (PSMA). Using a novel method, we also developed an assay to identify AR and AR-V7 simultaneously. Methods. Normal human whole blood samples were spiked with prostate cancer lines serving as model CTCs (mCTCs). Prostate cancer blood from a patient with advanced and known high CTC count were collected under an IRB-approved protocol. Blood was processed onto microscope slides and stained on an automated stainer with CTC detection assays incorporating 4 core parameters (nuclear dye, CD45, pan-cytokeratin, EpCAM) plus the following markers: (1) AR; (2) AR-V7; (3) AR and PSMA; (4) AR-V7 and PSMA; (5) AR and AR-V7. Each assay was applied to the cancer cell lines PC3, LNCaP, and 22RV1 and to the patient sample. An antibody denaturing process was used to sequentially amplify two rabbit monoclonals for the assay containing both AR and AR-V7. No-primary (diluent only) staining controls were run to confirm success of the denaturing step. Results. Staining of spike-in CTC models confirmed the reported AR and AR-V7 phenotype of the cell lines, supporting the specificity of the assays. When applied to an equivalent volume of the patient sample, the assays identified a mean (SD) of 36 (11) CTCs. In the assays staining AR, the mean percent of AR+ CTCs was 70% (range 61 - 86) and for the assays staining AR-V7, the percent of AR-V7+ CTCs was 30% (range 26 - 39). In the assay staining both AR and AR-V7, 10 of 38 CTCs were AR-V7+ (26%); all of these were AR+; 15 CTCs were only AR+ (39%). Conclusions. We have developed multi-parameter IF assays for detection of AR and AR-V7 in prostate CTCs, including the first assay we are aware of to simultaneously visualize AR and AR-V7. It has been validated in prostate cancer CTC models. The percentages of AR and AR-V7-positive CTCs identified in a patient sample with the assay are consistent with the percentages observed when AR and AR-V7 are detected in independent assays, supporting the accuracy of the simultaneous detection assay. All AR-V7-positive CTCs were also AR-positive, supporting specificity of AR-V7 staining.

Citation Format: Yao Sun, Daniel Campton, Arturo Ramirez, Tanisha Mojica, Alisa Clein, Celestia Higano, Daniel Sabath, Stephen Plymate, Eric Kaldjian. Development of a multi-parameter immunofluorescence assay for simultaneous detection of androgen receptor and androgen receptor variant 7 in prostate cancer circulating tumor cells [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 5230.

Evidence for feasibility of fetal trophoblastic cell-based noninvasive prenatal testing

Objective

The goal was to develop methods for detection of chromosomal and subchromosomal abnormalities in fetal cells in the mother's circulation at 10–16 weeks' gestation using analysis by array comparative genomic hybridization (CGH) and/or next‐generation sequencing (NGS).

Method

Nucleated cells from 30 mL of blood collected at 10–16 weeks' gestation were separated from red cells by density fractionation and then immunostained to identify cytokeratin positive and CD45 negative trophoblasts. Individual cells were picked and subjected to whole genome amplification, genotyping, and analysis by array CGH and NGS.

Results

Fetal cells were recovered from most samples as documented by Y chromosome PCR, short tandem repeat analysis, array CGH, and NGS including over 30 normal male cells, one 47,XXY cell from an affected fetus, one trisomy 18 cell from an affected fetus, nine cells from a trisomy 21 case, three normal cells and one trisomy 13 cell from a case with confined placental mosaicism, and two chromosome 15 deletion cells from a case known by CVS to have a 2.7 Mb de novo deletion.

Conclusion

We believe that this is the first report of using array CGH and NGS whole genome sequencing to detect chromosomal abnormalities in fetal trophoblastic cells from maternal blood. © 2016 The Authors. Prenatal Diagnosis published by John Wiley & Sons, Ltd.

What's already known about this topic?

Analysis of cell‐free DNA for noninvasive prenatal testing (NIPT) is widely practiced, and the frequency of amniocentesis and CVS has decreased.

However, cell‐free NIPT is not adequate for detecting smaller deletions and duplications with high specificity, sensitivity, and positive predictive value.

Although fetal nucleated red blood cells and trophoblastic cells are known to be present in the maternal circulation, it has not been possible to develop a reliable cytogenetic cell‐based form of NIPT.

What does this study add?

Fetal cytotrophoblasts were successfully recovered from maternal blood.

Although a clinical test has not been validated, for the first time, the feasibility of using array comparative genomic hybridization and next generation sequencing to detect chromosomal and subchromosomal abnormalities is demonstrated.

The results suggest the possibility of developing a cell‐based form of NIPT with ability to detect abnormalities with a similar accuracy as can currently be obtained with amniocentesis and CVS.

Abstract 4959: Multi-level analysis of prostate cancer circulating tumor cells allowing IHC-based identification, 6-parameter fluorescence phenotyping, and individual cell molecular analysis

Background. Analysis of circulating tumor cells (CTC) allows non-invasive investigation of prostate cancer biology and response to treatment. The primary level of analysis is the CTC count, which has been demonstrated to be prognostic of outcome. Deeper characterization of CTC phenotype and pertinent biomarkers can confirm cancer lineage and identify drug targets or drug-resistance markers. Single cell analysis of individual CTCs can provide genomic insight into cancer heterogeneity. RareCyte has developed AccuCyte® - CyteFinder® (AC-CF), an integrated technology platform for highly sensitive visual identification and retrieval of rare cells in blood by both immunohistochemistry (IHC) and immunofluorescence (IF) staining. Recently we have developed technology allowing 6-marker assays for broader phenotypic analysis.

Methods. Normal human whole blood samples were spiked with prostate cancer lines as model CTCs (mCTCs). Blood samples from University of Washington patients with advanced prostate cancer were collected under an IRB-approved protocol. Blood was processed using AccuCyte and the nucleated cell fraction was collected and spread onto microscope slides. Slides were stained on an automated stainer using (1) an IHC assay for cytokeratin, (2) a standard 4-wavelength IF assay (DAPI, CD45, cytokeratin and EpCAM) or (3) a novel 6-parameter IF assay using SYTOX-Orange (nuclear stain), cytokeratin, EpCAM, androgen receptor (AR), prostate-specific membrane antigen (PSMA) and CD45. An assay for AR variant 7 (ARv7) was applied to samples with mCTCs with the ARv7 splice variant. Percent recovery of IHC-stained slides (by blinded pathologist review) was compared to IF-stained slides (by CyteFinder image analysis). Individual IHC-stained CTCs were retrieved after on-slide visual identification and re-visualized after dispensing for confirmation. Whole genome amplification (WGA) of retrieved cells was performed, followed by X- and Y-chromosome gene-specific PCR.

Results. There was strong linear correlation between IF and IHC counts of mCTCs over a range of ∼25 - 100 cells/mL (R2 = 0.99). The 6-parameter IF assay was successfully applied to mCTC and clinical samples. AR and PSMA were co-expressed in the majority of epithelial-marker positive clinical CTCs. The ARv7 assay identified mCTCs that express the splice variant. Individual IHC-stained mCTCs spiked into female donor blood were demonstrated to be male after WGA and PCR.

Conclusions. Light microscope identification of IHC cytokeratin-positive mCTCs approximated IF identification. 6-parameter phenotyping of prostate cancer CTCs is feasible and allows identification of lineage-specific markers. IHC-stained cells can be individually retrieved from slides for genome amplification and molecular analysis.

Citation Format: Daniel Campton, Rachel Needham, Josh Nordberg, Arturo Ramirez, Nick Drovetto, Alisa Clein, Daniel E. Sabath, Jackie Stilwell, Eric Kaldjian. Multi-level analysis of prostate cancer circulating tumor cells allowing IHC-based identification, 6-parameter fluorescence phenotyping, and individual cell molecular analysis. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4959.

Abstract P4-01-21: Analysis and single-cell retrieval of circulating tumor cells to monitor treatment response and assess genotype in triple-negative breast cancer

Introduction: We used a high-recovery rare cell analysis and single-cell picking system to enrich, visualize, and isolate circulating tumor cells (CTCs) for genomic analysis from the blood of patients with advanced triple-negative breast cancer (TNBC) undergoing treatment with cisplatin as part of a study to intensively characterize TNBC. CTCs were evaluated regularly during treatment to monitor CTC burden and characteristics that could be associated with treatment response or disease progression, and perform single-cell mutational analysis to inform clinical decision making. Methods: Patients were enrolled in the study at the University of Washington Center for Cancer Innovation after informed consent for participation in investigation of their disease, including molecular analysis of multiple biopsies of accessible tumor. CTCs were evaluated prior to treatment and tracked longitudinally. Density-based enrichment of blood cells was performed using the AccuCyte tube, float and collector system. Collected cells were processed and applied to microscopic slides. Fluorescently labeled antibodies to cytokeratin, CD45 and EpCAM, and a nuclear dye were applied to samples using an automated slide stainer. Slides were scanned on a digital microscope and candidate CTCs identified using image analysis software. CTCs were verified by appropriate morphology and expression of epithelial and nuclear stains without CD45 expression. Other antibodies used to characterize cells included Her2, EGFR, and Ki-67. A mutation hypothesized to lead to the activation of ROS1 was identified in the cancer cells isolated from the bone marrow of one patient. CTCs were picked using our integrated semi-automated system and evaluated for the ROS1 variant using whole genome amplification followed by nested PCR and Sanger sequencing. Results: Seven patients have been enrolled to date. At least 1 CTC/mL has been found in all patients. Pre-treatment CTC levels in the patient with the ROS1 mutation were extremely high (1500/mL). One week after treatment, CTC levels spiked to more than 5000/mL. CTC counts then dropped exponentially to 9/mL after 4 months. CTC clusters and Ki-67 positive cells also decreased during therapy. Treatment with cisplatin was discontinued in this patient due to toxicity and progression, and CTC levels increased to nearly 9000/mL over 4 months. The ROS1 mutation was found in approximately 50% of individually picked CTCs before treatment with crizotinib, a ROS1 inhibitor. A second patient was found to have somatic loss of BRCA1, and was therefore treated with the PARP inhibitor, veliparib. CTC levels increased during veliparib treatment up to 13/mL. The same patient was subsequently treated with ponatinib, an FGFR inhibitor, based on the identification of two linked somatic missense mutations involving FGFR2 (S252W and Y375C). After beginning ponatinib, CTCs fell to undetectable levels. Conclusions: Analysis of CTCs may provide a non-invasive measure of cancer progression/response and the molecular evolution of tumor cells in patients with TNBC. Single-cell CTC retrieval after slide-based immunofluorescent visualization is compatible with whole genome amplification and sequencing methods.

Citation Format: Arturo Ramirez, Daniel Campton, Elisabeth Mahen, Sibel Blau, Anthony Blau, Eric Kaldjian, Jackie Stilwell. Analysis and single-cell retrieval of circulating tumor cells to monitor treatment response and assess genotype in triple-negative breast cancer [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P4-01-21.