Interleukin-6 Induces Stem Cell Propagation through Liaison with the Sortilin-Progranulin Axis in Breast Cancer

Unraveling the complex network between cancer cells and their tumor microenvironment is of clinical importance, as it might allow for the identification of new targets for cancer treatment. Cytokines and growth factors secreted by various cell types present in the tumor microenvironment have the potential to affect the challenging subpopulation of cancer stem cells showing treatment-resistant properties as well as aggressive features. By using various model systems, we investigated how the breast cancer stem cell-initiating growth factor progranulin influenced the secretion of cancer-associated proteins. In monolayer cultures, progranulin induced secretion of several inflammatory-related cytokines, such as interleukin (IL)-6 and -8, in a sortilin-dependent manner. Further, IL-6 increased the cancer stem fraction similarly to progranulin in the breast cancer cell lines MCF7 and MDA-MB-231 monitored by the surrogate mammosphere-forming assay. In a cohort of 63 patient-derived scaffold cultures cultured with breast cancer cells, we observed significant correlations between IL-6 and progranulin secretion, clearly validating the association between IL-6 and progranulin also in human-based microenvironments. In conclusion, the interplay between progranulin and IL-6 highlights a dual breast cancer stem cell-promoting function via sortilin, further supporting sortilin as a highly relevant therapeutic target for aggressive breast cancer.

Optimized alginate-based 3D printed scaffolds as a model of patient derived breast cancer microenvironments in drug discovery

The cancer microenvironment influences tumor progression and metastasis and is pivotal to consider when designingin vivo-like cancer models. Current preclinical testing platforms for cancer drug development are mainly limited to 2D cell culture systems that poorly mimic physiological environments and traditional, low throughput animal models. The aim of this work was to produce a tunable testing platform based on 3D printed scaffolds (3DPS) with a simple geometry that, by extracellular components and response of breast cancer reporter cells, mimics patient-derived scaffolds (PDS) of breast cancer. Here, the biocompatible polysaccharide alginate was used as base material to generate scaffolds consisting of a 3D grid containing periostin and hydroxyapatite. Breast cancer cell lines (MCF7 and MDA-MB-231) produced similar phenotypes and gene expression levels of cancer stem cell, epithelial-mesenchymal transition, differentiation and proliferation markers when cultured on 3DPS and PDS, contrasting conventional 2D cultures. Importantly, cells cultured on 3DPS and PDS showed scaffold-specific responses to cytotoxic drugs (doxorubicin and 5-fluorouracil) that were different from 2D cultured cells. In conclusion, the data presented support the use of a tunable alginate-based 3DPS as a tumor model in breast cancer drug discovery.

Patient-derived scaffolds influence secretion profiles in cancer cells mirroring clinical features and breast cancer subtypes

BACKGROUND

Breast cancer is a common malignancy with varying clinical behaviors and for the more aggressive subtypes, novel and more efficient therapeutic approaches are needed. Qualities of the tumor microenvironment as well as cancer cell secretion have independently been associated with malignant clinical behaviors and a better understanding of the interplay between these two features could potentially reveal novel targetable key events linked to cancer progression.

METHODS

A newly developed human derived in vivo-like growth system, consisting of decellularized patient-derived scaffolds (PDSs) recellularized with standardized breast cancer cell lines (MCF7 and MDA-MB-231), were used to analyze how 63 individual patient specific microenvironments influenced secretion determined by proximity extension assays including 184 proteins and how these relate to clinical outcome.

RESULTS

The secretome from cancer cells in PDS cultures varied distinctly from cells grown as standard monolayers and besides a general increase in secretion from PDS cultures, several secreted proteins were only detectable in PDSs. Monolayer cells treated with conditioned media from PDS cultures, further showed increased mammosphere formation demonstrating a cancer stem cell activating function of the PDS culture induced secretion. The detailed secretomic profiles from MCF7s growing on 57 individual PDSs differed markedly but unsupervised clustering generated three separate groups having similar secretion profiles that significantly correlated to different clinical behaviors. The secretomic profile that associated with cancer relapse and high grade breast cancer showed induced secretion of the proteins IL-6, CCL2 and PAI-1, all linked to cancer stem cell activation, metastasis and priming of the pre-metastatic niche. Cancer promoting pathways such as "Suppress tumor immunity" and "Vascular and tissue remodeling" was also linked to this more malignant secretion cluster.

CONCLUSION

PDSs repopulated with cancer cells can be used to assess how cancer secretion is effected by specific and varying microenvironments. More malignant secretion patterns induced by specific patient based cancer microenvironments could further be identified pinpointing novel therapeutic opportunities targeting micro environmentally induced cancer progression via secretion of potent cytokines. Video abstract.

Characterization of cell-free breast cancer patient-derived scaffolds using liquid chromatography-mass spectrometry/mass spectrometry data and RNA sequencing data

Patient-derived scaffolds (PDSs) generated from primary breast cancer tumors can be used to model the tumor microenvironment in vitro. Patient-derived scaffolds are generated by repeated detergent washing, removing all cells. Here, we analyzed the protein composition of 15 decellularized PDSs using liquid chromatography-mass spectrometry/mass spectrometry. One hundred forty-three proteins were detected and their relative abundance was calculated using a reference sample generated from all PDSs. We performed heatmap analysis of all the detected proteins to display their expression patterns across different PDSs together with pathway enrichment analysis to reveal which processes that were connected to PDS protein composition. This protein dataset together with clinical information is useful to investigators studying the microenvironment of breast cancers. Further, after repopulating PDSs with either MCF7 or MDA-MB-231 cells, we quantified their gene expression profiles using RNA sequencing. These data were also compared to cells cultured in conventional 2D conditions, as well as to cells cultured as xenografts in immune-deficient mice. We investigated the overlap of genes regulated between these different culture conditions and performed pathway enrichment analysis of genes regulated by both PDS and xenograft cultures compared to 2D in both cell lines to describe common processes associated with both culture conditions. Apart from our described analyses of these systems, these data are useful when comparing different experimental model systems. Downstream data analyses and interpretations can be found in the research article “Patient-derived scaffolds uncover breast cancer promoting properties of the microenvironment” [1].

Abstract P1-04-01: Breast cancer patient derived scaffolds as a platform for studying cancer promoting properties of the microenvironment

Despite great efficiencies of today’s anti-cancer therapies in breast cancer medicine, recurrences and metastasis still remains a major challenge. The tumor initiating population of cancer stem cells (CSC) is believed to promote metastasis and drug resistance, suggesting that selectively targeting CSC and their niche may be a potential beneficial therapeutic strategy. However, specific driving factors in the microenvironment influencing the CSC niche remains unknown. To study the influence of specific cancer microenvironments, we have developed a novel three-dimensional cell culture platform, using cell-free patient derived scaffolds (PDS) from decellularized breast cancer tumors. We confirmed that our novel patient derived scaffold (PDS) recapitulates the native microenvironment where the cancer cells originate and, retains their biological properties. Our data demonstrate that culturing breast cancer cell lines in PDSs promotes CSC and EMT-like properties and decreases proliferation, similarly to in vivo conditions. Additionally, global gene expression profiling revealed that PDS cultures exhibit transcriptional patterns more similar to patient derived xenografts than to traditional monolayer cultures. Moreover, we analyzed the expression of cells cultured in 108 PDSs made from breast cancer tumors with clinical follow-up data, using a gene panel representative of relevant breast cancer related processes. This revealed that expression changes of several EMT markers and other CSC related genes in the PDS cultured cancer cells were correlated to clinical parameters such as grade, lymph node metastasis, patient survival and disease recurrences. Altogether, our data shows that PDS can reveal unique additional information about the malignancy-inducing properties of specific tumor microenvironments, potentially provides a complementary diagnosis tool for breast cancer tumors in vitro, and is a promising platform for drug screening of anti-cancer therapies.

Citation Format: Elena Garre, Anna Gustafsson, Maria del Carmen Leiva-Arrabal, Paul Fitzpatrick, Pernilla Gregersson, Anders Ståhlberg, Göran Landberg. Breast cancer patient derived scaffolds as a platform for studying cancer promoting properties of the microenvironment [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P1-04-01.

Abstract P6-06-14: Analysis of secreted proteome in an in vivo like human 3D model of breast cancer

Background: Breast cancer is the most common form of cancer amongst women and affects millions worldwide each year. The tumor micro environment plays a key role in cancer progression and disease outcome of which a highly important factor is the secreted proteome which includes cytokines, chemokines and other proteins. Cancer cells influence neighboring cells by both autocrine and paracrine secretion which affects cancer cell characteristics such as stem-like properties, proliferation and metastatic capacity. Due to the importance of cancer cell signaling and cell to cell communication, when studying the cancer cell secretome in a three-dimensional environment new signaling pathways and new possible drug targets can be investigated.

Methods: To understand the complexity of breast cancer cell secretion, the human in vivo like system patient derived scaffolds (PDS) was used as a modeling system whereby patient specific extracellular matrix mediated cellular secretion in both ERα+ and ERα- cell lines were investigated. 54 human breast cancer tumors were decellularized and the PDS were repopulated with either MCF7 or MDA-MB-231 cells. Cell lines were grown on scaffolds for 21 days. At day 16 cell media was changed and at day 21 conditioned media was collected for secretome analysis. Multiplex Proximity Extension Assay (OLINK, Uppsala Sweden) was performed on conditioned media and 184 proteins were analyzed for each sample.

Results: The secretome from cells grown in PDS culture differs distinctly from the secretome from cells cultured in standard monolayer cultures, both in numbers and amount of secreted proteins. Secreted proteins from cells grown in PDS cultures were also shown to increase the cancer stem cell population compared to secretome from cells cultivated in monolayer culture. By comparing secretomic profiles from MCF7 cells grown in 54 PDSs, three clusters were created with an unsupervised clustering method. When these three clusters were correlated to clinical information about the specific tumors in each cluster, patients in one of the clusters were found to have a significantly lower chance of relapse-free survival and a higher frequency of high-grade tumors. Further, cells grown in PDS from this cluster also showed a different genetic profile with increased expression of markers related to epithelial-mesenchymal transition.

Conclusion: Breast cancer cells grown in a three-dimensional in vivo-like model have a distinct different secretomic profile compare to monolayer cultured cells and the secretion can be related to the original characteristics of the breast tumor. This highlights the importance of the tumor microenvironment induced secretion and the possibility to target secreted proteins as a therapeutic strategy.

Citation Format: Emma Persson, Pernilla Gregersson, Paul Fitzpatrick, Anna Gustafsson, Anders Ståhlberg, Göran Landberg. Analysis of secreted proteome in an in vivo like human 3D model of breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P6-06-14.

Patient-derived scaffolds uncover breast cancer promoting properties of the microenvironment

Tumor cells interact with the microenvironment that specifically supports and promotes tumor development. Key components in the tumor environment have been linked to various aggressive cancer features and can further influence the presence of subpopulations of cancer cells with specific functions, including cancer stem cells and migratory cells. To model and further understand the influence of specific microenvironments we have developed an experimental platform using cell-free patient-derived scaffolds (PDSs) from primary breast cancers infiltrated with standardized breast cancer cell lines. This PDS culture system induced a series of orchestrated changes in differentiation, epithelial-mesenchymal transition, stemness and proliferation of the cancer cell population, where an increased cancer stem cell pool was confirmed using functional assays. Furthermore, global gene expression profiling showed that PDS cultures were similar to xenograft cultures. Mass spectrometry analyses of cell-free PDSs identified subgroups based on their protein composition that were linked to clinical properties, including tumor grade. Finally, we observed that an induction of epithelial-mesenchymal transition-related genes in cancer cells growing on the PDSs were significantly associated with clinical disease recurrences in breast cancer patients. Patient-derived scaffolds thus mimics in vivo-like growth conditions and uncovers unique information about the malignancy-inducing properties of tumor microenvironment.

Hypoxia-induced secretion stimulates breast cancer stem cell regulatory signalling pathways

It is well known that tumour cells are dependent on communication with the tumour microenvironment. Previously, it has been shown that hypoxia (HX) induces pronounced, diverse and direct effects on cancer stem cell (CSC) qualities in different breast cancer subtypes. Here, we describe the mechanism by which HX-induced secretion influences the spreading of CSCs. Conditioned media (CM) from estrogen receptor (ER)-α-positive hypoxic breast cancer cell cultures increased the fraction of CSCs compared to normal growth conditions, as determined using sets of CSC assays and model systems. In contrast, media from ERα-negative hypoxic cell cultures instead decreased this key subpopulation of cancer cells. Further, there was a striking overrepresentation of JAK-STAT-associated cytokines in both the ERα-positive and ERα-negative linked hypoxic responses as determined by a protein screen of the CM. JAK-STAT inhibitors and knockdown experiments further supported the hypothesis that this pathway is critical for the CSC-activating and CSC-inactivating effects induced by hypoxic secretion. We also observed that the interleukin-6-JAK2-STAT3 axis was specifically central for the ERα-negative hypoxic behaviour. Our results underline the importance of considering breast cancer subtypes in treatments targeting JAK-STAT or HX-associated processes and indicate that HX is not only a confined tumour biological event, but also influences key tumour properties in widespread normoxic microenvironments.

Abstract P5-07-08: Withdrawn

This abstract was withdrawn by the authors.

Citation Format: Persson E, Gregersson P, Fitzpatrick P, Ståhlberg A, Landberg G. Withdrawn [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 P5-07-08.

Abstract P2-06-11: Sortilin targeted therapy in breast cancer with elevated progranulin expression

Background: A major challenge concerning breast cancer therapy is the occasional lack of effects using drugs that target cancer cells unspecifically. One possible explanation for this treatment failure is the existence of the small subpopulation of breast cancer stem cells that are believed to be more resistant towards conventional therapy and possesses the ability to drive tumor formation and disease progression. Cytokines secreted by nearby cells and other factors in the surrounding tumor microenvironment further stimulate the cancer cells, contributing to a heterogeneous and potentially more treatment resistant tumor. Thus, a more specific treatment approach targeting the breast cancer stem cell niche is crucial in preventing disease recurrences. In a cytokine screen, we identified progranulin as one of the main compounds secreted from cells exposed to hypoxia, leading to cancer stem cell propagation. Progranulin is involved in biological processes such as wound healing, inflammation and cancer progression. Progranulin and its receptor sortilin are known to be highly expressed in subgroups of breast cancer and are further associated with a clinically aggressive phenotype.

Methods/Results: By carrying out a number of in vitro and in vivo like screening assays, we demonstrate that progranulin influences the stem cell population in breast cancer and is responsible for spreading a cancer stem cell promoting signal to normoxic tumor areas. In breast cancer, progranulin induces a dedifferentiation process in the receiving cancer cells and expression of cancer stem cell markers together with an EMT-associated gene expression profile, leading to cancer stem cell expansion. By using siRNA and pharmacological inhibition of sortilin, we show that sortilin is a functional receptor of progranulin and is responsible for driving progranulin induced breast cancer stem cell propagation. Supporting the role of progranulin in cancer progression, administration of progranulin in immunocompromised mice induce lung metastasis in our breast cancer xenograft models. The use of different approaches for blocking sortilin, such as sortilin inhibitors, down-modulators or sortilin-targeted antibodies can prevent this dedifferentiation process, both in vitro and in vivo, making the tumor cells less aggressive and metastatic.

Conclusion: Targeting progranulin through its associated receptors is a potential therapeutic strategy for the treatment of patients with breast tumors having elevated progranulin or sortilin expression. By inhibiting the secretion based breast cancer progression, we could possibly block the formation of metastasis and cancer cell infiltration.

Citation Format: Berger K, Rhost S, Hughes E, Harrison H, Rafnsdottir S, Jacobsson H, Gregersson P, Magnusson Y, Fitzpatrick P, Andersson D, Ståhlberg A, Landberg G. Sortilin targeted therapy in breast cancer with elevated progranulin expression [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 P2-06-11.

Sortilin inhibition limits secretion-induced progranulin-dependent breast cancer progression and cancer stem cell expansion

Background

Cancer progression is influenced by genetic aberrations in the cancer cell population as well as by other factors including the microenvironment present within a tumour. Direct interactions between various cell types as well as cellular signalling via secreted cytokines can drive key tumourigenic properties associated with disease progression and treatment resistance. Also, cancer stem cell functions are influenced by the microenvironment. This challenging subset of cells has been linked to malignant properties. Within a screen, using in vivo like growth conditions, we identified progranulin as a highly secreted cytokine affecting cancer stem cells in breast cancer. This cytokine is known to play a role in numerous biological and tumour-related processes including therapy resistance in a range of cancer types.

Methods

Different in vitro and in vivo relevant conditions were used to validate breast cancer stem cell expansion mediated by progranulin and its receptor sortilin. Small interfering ribonucleic acid (siRNA) and pharmacological inhibition of sortilin were used to elucidate the role of sortilin as a functional receptor during progranulin-induced breast cancer stem cell propagation, both in vitro and in vivo, using breast cancer xenograft models. In addition, single-cell gene expression profiling as well as a Sox2 reporter breast cancer cell line were used to validate the role of dedifferentiation mediated by progranulin.

Results

In various in vivo-like screening assays, progranulin was identified as a potent cancer stem cell activator, highly secreted in ERα-negative breast cancer as well as in ERα-positive breast cancer under hypoxic adaptation. Progranulin exposure caused dedifferentiation as well as increased proliferation of the cancer stem cell pool, a process that was shown to be dependent on its receptor sortilin. Subcutaneous injections of progranulin or its active domain (GRN A) induced lung metastases in breast cancer xenograft models, supporting a major role for progranulin in cancer progression. Importantly, an orally bioavailable small molecule (AF38469) targeting sortilin, blocked GRN A-induced lung metastases and prevented cancer cell infiltration of the skin.

Conclusion

The collective results suggest that sortilin targeting represents a potential novel breast cancer therapy approach inhibiting tumour progression driven by secretion and microenvironmental influences.

Electronic supplementary material

The online version of this article (10.1186/s13058-018-1060-5) contains supplementary material, which is available to authorized users.

Generation of a functional humanized Delta-like ligand 4 transgenic mouse model

Humanized mouse models are important tools in many areas of biological drug development including, within oncology research, the development of antagonistic antibodies that have the potential to block tumor growth by controlling vascularization and are key to the generation of in vivo proof-of-concept efficacy data. However, due to cross reactivity between human antibodies and mouse target such studies regularly require mouse models expressing only the human version of the target molecule. Such humanized knock-in/knock-out, KIKO, models are dependent upon the generation of homozygous mice expressing only the human molecule, compensating for loss of the mouse form. However, KIKO strategies can fail to generate homozygous mice, even though the human form is expressed and the endogenous mouse locus is correctly targeted. A typical strategy for generating KIKO mice is by ATG fusion where the human cDNA is inserted downstream of the endogenous mouse promoter elements. However, when adopting this strategy it is possible that the mouse promoter fails to express the human form in a manner compensating for loss of the mouse form or alternatively the human protein is incompatible in the context of the mouse pathway being investigated. So to understand more around the biology of KIKO models, and to overcome our failure with a number of ATG fusion strategies, we developed a range of humanized models focused on Delta-like 4 (Dll4), a target where we initially failed to generate a humanized model. By adopting a broader biologic strategy, we successfully generated a humanized DLL4 KIKO which led to a greater understanding of critical biological aspects for consideration when developing humanized models.

Identification of Distinct Breast Cancer Stem Cell Populations Based on Single-Cell Analyses of Functionally Enriched Stem and Progenitor Pools

The identification of breast cancer cell subpopulations featuring truly malignant stem cell qualities is a challenge due to the complexity of the disease and lack of general markers. By combining extensive single-cell gene expression profiling with three functional strategies for cancer stem cell enrichment including anchorage-independent culture, hypoxia, and analyses of low-proliferative, label-retaining cells derived from mammospheres, we identified distinct stem cell clusters in breast cancer. Estrogen receptor (ER)α+ tumors featured a clear hierarchical organization with switch-like and gradual transitions between different clusters, illustrating how breast cancer cells transfer between discrete differentiation states in a sequential manner. ERα− breast cancer showed less prominent clustering but shared a quiescent cancer stem cell pool with ERα+ cancer. The cellular organization model was supported by single-cell data from primary tumors. The findings allow us to understand the organization of breast cancers at the single-cell level, thereby permitting better identification and targeting of cancer stem cells.

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ERα+ and ERα− breast cancer stem cells share a quiescent cancer stem cell pool

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Single-cell analysis identified distinct cancer stem cell populations in breast cancer

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Identified ERα+ breast cancer cell populations were hierarchically organized

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Switch-like and gradual transitions exist between ERα+ stem and progenitor pools

Abstract LB-49: Defining hierarchical organization of breast cancer cells and cancer activated fibroblasts using single-cell gene expression profiling: switch-like and transient transitions between novel stem cell and progenitor pools

The cancer stem cell (CSC) model holds that cancers are organized in a hierarchical structure and derived from cellular populations with stem cell properties. CSC characteristics include self-renewal, tumorigenicity, multi-lineage differentiation as well as increased resistance to radio- and chemotherapy-induced cell death. In order to better understand the complex hierarchical structure of breast cancer cells in vivo as well as phenotypes of stromal cells as cancer associated fibroblasts, tools need to be developed, enabling analyses of key regulators and biomarkers on a single-cell level. We therefore established single-cell reverse transcription quantitative real-time PCR and gene expression profiling, including more than 100 key regulators associated with the cell cycle, differentiation, EMT, stemness and fibroblast activation and performed extensive single-cell PCR analyses, using cell lines and primary breast cancer samples.

Three strategies were used to enrich for cancer stem cells and progenitor populations corresponding to 1) cells surviving anchorage-independent growth conditions, 2) cells in mammospheres showing few cell divisions, defined by a cell division tracker and 3) cells grown under hypoxic conditions. All methods have earlier been shown to enrich for cells that have an increased cancer initiating ability in mouse model systems. Interestingly, all strategies increased two separate tumor subpopulations defined by lower proliferative features and various EPCAM, ERBB2, CDH1, ID1, ABCG2, POU5F1, NANOG and SOX2 levels. Besides, a clear switch-like transition between the various populations, a transition state linking the cancer stem cell and progenitor populations with the high proliferative main cluster was observed. When specifically analyzing the few cells that had only undergone one asymmetrical cell division in 5 days mammosphere cultures, it was clear that this potential stem cell pool had a distinctive expression profile based on the included key regulators.

We next analyzed immortalized primary fibroblasts and tumor activated counterparts using single-cell PCR analyses. The two cell types clearly separated from each other and showed various activation states defined by key regulators as COL1A1, ALDH1A3, TGFB, PDGFA, ACTA2, CXCL12 and cell cycle regulators. The data support a continuing transition towards myofibroblast differentiation with gradual loss of proliferation, whereas the activation markers peak in an intermediate state before entering a final low proliferative condition. When analyzing primary tumors we observed distinct clusters of epithelial cells and fibroblasts supporting the validity of the defined assay. A detailed description of primary breast cancer samples and important microenvironmental components combined with functional assays on a single cell level are now ongoing.

Within this comprehensive program we have identified diverse previously unknown CSC/progenitor pools or distinct cellular states and we are now able to model how cells actually transfer between various differentiation and stem cells states, thereby better understanding the hierarchical composition of breast cancer on a single cell level.

Citation Format: Anders Ståhlberg, Nina Akrap, Daniel Andersson, Pernilla Gregersson, Susann Busch, Göran P. Landberg. Defining hierarchical organization of breast cancer cells and cancer activated fibroblasts using single-cell gene expression profiling: switch-like and transient transitions between novel stem cell and progenitor pools. [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 LB-49. doi:10.1158/1538-7445.AM2014-LB-49