Gasdermin B over-expression modulates HER2-targeted therapy resistance by inducing protective autophagy through Rab7 activation

Gasdermin B; HER2 breast cancer; Protective autophagyGasdermin B; Càncer de mama HER2; Autofàgia protectoraGasdermin B; Cáncer de mama HER2; Autofagia protectoraBackground Gasdermin B (GSDMB) over-expression promotes poor prognosis and aggressive behavior in HER2 breast cancer by increasing resistance to therapy. Decoding the molecular mechanism of GSDMB-mediated drug resistance is crucial to identify novel effective targeted treatments for HER2/GSDMB aggressive tumors. Methods Different in vitro approaches (immunoblot, qRT-PCR, flow cytometry, proteomic analysis, immunoprecipitation, and confocal/electron microscopy) were performed in HER2 breast and gastroesophageal carcinoma cell models. Results were then validated using in vivo preclinical animal models and analyzing human breast and gastric cancer samples. Results GSDMB up-regulation renders HER2 cancer cells more resistant to anti-HER2 agents by promoting protective autophagy. Accordingly, the combination of lapatinib with the autophagy inhibitor chloroquine increases the therapeutic response of GSDMB-positive cancers in vitro and in zebrafish and mice tumor xenograft in vivo models. Mechanistically, GSDMB N-terminal domain interacts with the key components of the autophagy machinery LC3B and Rab7, facilitating the Rab7 activation during pro-survival autophagy in response to anti-HER2 therapies. Finally, we validated these results in clinical samples where GSDMB/Rab7/LC3B co-expression associates significantly with relapse in HER2 breast and gastric cancers. Conclusion Our findings uncover for the first time a functional link between GSDMB over-expression and protective autophagy in response to HER2-targeted therapies. GSDMB behaves like an autophagy adaptor and plays a pivotal role in modulating autophagosome maturation through Rab7 activation. Finally, our results provide a new and accessible therapeutic approach for HER2/GSDMB + cancers with adverse clinical outcome.This study has been supported by the Ministerio de Ciencia, Innovación y Universidades, Agencia Estatal de Investigación (PID2019-104644RB-I00) -GMB-, the Instituto de Salud Carlos III (CIBERONC, CB16/12/00449 -JA-, CB16/12/00231 -DLN- and CB16/12/00295 -GMB-, PI19/01181 -JA-, PI18/00795, CP17/00063 and RTI2018-095611-A-I00 -DLN- and ERA-NET TRANSCAN-2 -JA- [all partly supported by FEDER funds]) and by the AECC Scientific Foundation (FC_AECC PROYE19036MOR -GMB- and LABAE19004LLOB -DLN-). Furthermore, this work was supported by Breast Cancer Research Foundation (BCRF-19–08) -JA-. We are also grateful to the CERCA Programme (Generalitat de Catalunya) for institutional support. MGC and DS contracts are funded by CIBERONC, KG is a recipient of a PFIS fellowship (FI19/00188), RRB is recipient of a Ramón y Cajal grant (RyC-2016–19671) and DLN is recipient of a Miguel Servet grant (MS17/00063) (all partly supported by FEDER funds). We are also grateful to MD Anderson BIOBANK for providing tumor samples. The bank (reference # B.0000745) belongs to the National Registry of Biobanks coordinated by the Carlos III Health Institute

Epstein–Barr Virus+ B Cells in Breast Cancer Immune Response: A Case Report

B cells; Epstein–Barr virus; Breast cancerCélulas B; Virus de Epstein-Barr; Cáncer de mamaLimfòcits B; Virus d'Epstein-Barr; Càncer de mamaEBV-specific T cells have been recently described to be involved in fatal encephalitis and myocarditis in cancer patients after immune checkpoint therapies. Here, we report the study of a human triple-negative breast cancer tumor (TNBC) and EBV-transformed B cells obtained from a patient-derived xenograft (PDX) that progressed into a lymphocytic neoplasm named xenograft-associated B-cell lymphoma (XABCL). T-cell receptor (TCR) high-throughput sequencing was performed to monitor the T-cell clonotypes present in the different samples. Forty-three T-cell clonotypes were found infiltrating the XABCL tissue after three passes in mice along 6 months. Eighteen of these (42%) were also found in the TNBC biopsy. TCR infiltrating the XABCL tissue showed a very restricted T-cell repertoire as compared with the biopsy-infiltrating T cells. Consequently, T cells derived from the TNBC biopsy were expanded in the presence of the B-cell line obtained from the XABCL (XABCL-LCL), after which the TCR repertoire obtained was again very restricted, i.e., only certain clonotypes were selected by the B cells. A number of these TCRs had previously been reported as sequences involved in infection, cancer, and/or autoimmunity. We then analyzed the immunopeptidome from the XABCL-LCL, to identify putative B-cell-associated peptides that might have been expanding these T cells. The HLA class I and class II-associated peptides from XABCL-LCL were then compared with published repertoires from LCL of different HLA typing. Proteins from the antigen processing and presentation pathway remained significantly enriched in the XABCL-LCL repertoire. Interestingly, some class II-presented peptides were derived from cancer-related proteins. These results suggest that bystander tumor-infiltrating EBV+ B cells acting as APC may be able to interact with tumor-infiltrating T cells and influence the TCR repertoire in the tumor site.This project was funded by Roche Farma, S.A. grant SP181123001 and the Spanish Ministry of Science, Innovation and Universities grant RTI2018-097414-B-I00. Partial financial support was received from the “El Paseíco de la Mama” 2015. This study received partial funding from Roche Farma, S.A. The funders were not involved in the study design, collection, analysis, interpretation of data, the writing of this article, or the decision to submit it for publication

Evaluation of triple negative breast cancer with heterogeneous immune infiltration

Intratumor heterogeneity; Transcriptomics; Tumor-infiltrating lymphocytesHeterogeneïtat intratumoral; Transcriptòmica; Limfòcits infiltrants de tumorsHeterogeneidad intratumoral; Transcriptómica; Linfocitos infiltrantes de tumoresIntroduction: Tumor infiltrating lymphocytes (TILs) are known to be a prognostic and predictive biomarker in breast cancer, particularly in triple negative breast cancer (TNBC) patients. International guidelines have been proposed to evaluate them in the clinical setting as a continuous variable, without a clear defined cut-off. However, there are scenarios where the immune infiltration is heterogeneous that some areas of the patient’s tumour have high numbers of TILs while other areas completely lack them. This spontaneous presentation of a heterogeneous immune infiltration could be a great opportunity to study why some tumours present TILs at diagnosis but others do not, while eliminating inter patient’s differences. Methods: In this study, we have identified five TNBC patients that showed great TIL heterogeneity, with areas of low (≤5%) and high (≥50%) numbers of TILs in their surgical specimens. To evaluate immune infiltration heterogeneity, we performed and analyzed bulk RNA-sequencing in three independent triplicates from the high and low TIL areas of each patient. Results: Gene expression was homogeneous within the triplicates in each area but was remarkable different between TILs regions. These differences were not only due to the presence of TILs as there were other non-inflammatory genes and pathways differentially expressed between the two areas. Discussion: This highlights the importance of intratumour heterogeneity driving the immune infiltration, and not patient’s characteristics like the HLA phenotype, germline DNA or immune repertoire.This research has received funding from “Contigo contra el cancer de la mujer” Foundation and FERO Foundation

Vitamin D analogues exhibit antineoplastic activity in breast cancer patient-derived xenograft cells

Despite advances in breast cancer (BC) treatment, its mortality remains high due to intrinsic or acquired resistance to therapy. Several ongoing efforts are being made to develop novel drugs to treat this pathology with the aim to overcome resistance, prolong patient survival and improve their quality of life. We have previously shown that the non-hypercalcemic vitamin D analogues EM1 and UVB1 display antitumor effects in preclinical studies employing conventional cell lines and animal models developed from these cells. In this work, we explored the antitumor effects of EM1 and UVB1 employing BC cells derived from patient-derived xenografts (PDXs), which are a powerful preclinical tool for testing new drugs. We demonstrated that the analogues reduced the viability of HER2-positive and Triple Negative BC-PDXs. Moreover, using an in vitro model of acquired resistance to Trastuzumab-emtansine, UVB1 displayed anti-proliferative actions under 2D and 3D culture conditions. It inhibited both formation and growth of established organoids. In addition, a direct correlation between UVB1 antitumor effects and VDR expression in PDXs was found. In conclusion, all the results reinforce the potential use of these vitamin D analogues as antitumor agents to treat HER2-positive and Triple Negative BC.Fil: Ferronato, María Julia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Investigaciones Bioquímicas de Bahía Blanca. Universidad Nacional del Sur. Instituto de Investigaciones Bioquímicas de Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; ArgentinaFil: Nadal, Serrano Mercedes. Universidad Autonoma de Barcelona. Hospital Vall D' Hebron. Instituto de Investigación Vall D'hebron; EspañaFil: Arenas Lahuerta, Enrique Javier. Universidad Autonoma de Barcelona. Hospital Vall D' Hebron. Instituto de Investigación Vall D'hebron; EspañaFil: Morales, Cristina Bernadó. Universidad Autónoma de Barcelona. Hospital Vall D' Hebron; EspañaFil: Paolillo, Giuliana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Investigaciones Bioquímicas de Bahía Blanca. Universidad Nacional del Sur. Instituto de Investigaciones Bioquímicas de Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; ArgentinaFil: Martinez Sabadell, Aliguer Alex. Universidad Autónoma de Barcelona. Hospital Vall D' Hebron; EspañaFil: Mascaró, Marilina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Investigaciones Bioquímicas de Bahía Blanca. Universidad Nacional del Sur. Instituto de Investigaciones Bioquímicas de Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; ArgentinaFil: Vitale, Cristian Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; ArgentinaFil: Fall, Yagamare. Universidad de Vigo; EspañaFil: Arribas, Joaquín. Universidad Autónoma de Barcelona. Hospital Vall D' Hebron; España. Universitat Autònoma de Barcelona; España. Centro de Investigación Biomédica en Red de Cáncer; España. Institució Catalana de Recerca i Estudis Avancats; EspañaFil: Facchinetti, María Marta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Investigaciones Bioquímicas de Bahía Blanca. Universidad Nacional del Sur. Instituto de Investigaciones Bioquímicas de Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; ArgentinaFil: Curino, Alejandro Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Investigaciones Bioquímicas de Bahía Blanca. Universidad Nacional del Sur. Instituto de Investigaciones Bioquímicas de Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; Argentin

Gasdermin B expression predicts poor clinical outcome in HER2-positive breast cancer

Altres ajuts: This work has been supported by the Community of Madrid (grant S2010/BMD-2303 to GMB), the Breast Cancer Research Foundation (BCRF) to JA. Alba Mota is a predoctoral student supported by a FPU fellowship (Spanish Ministry of Education, Culture and Sport). David Sarrio is a postdoctoral researcher funded by the AECC Scientific Foundation.Around, 30-40% of HER2-positive breast cancers do not show substantial clinical benefit from the targeted therapy and, thus, the mechanisms underlying resistance remain partially unknown. Interestingly, ERBB2 is frequently co-amplified and co-expressed with neighbour genes that may play a relevant role in this cancer subtype. Here, using an in silico analysis of data from 2,096 breast tumours, we reveal a significant correlation between Gasdermin B (GSDMB) gene (located 175 kilo bases distal from ERBB2) expression and the pathological and clinical parameters of poor prognosis in HER2-positive breast cancer. Next, the analysis of three independent cohorts (totalizing 286 tumours) showed that approximately 65% of the HER2-positive cases have GSDMB gene amplification and protein over-expression. Moreover, GSDMB expression was also linked to poor therapeutic responses in terms of lower relapse free survival and pathologic complete response as well as positive lymph node status and the development of distant metastasis under neoadjuvant and adjuvant treatment settings, respectively. Importantly, GSDMB expression promotes survival to trastuzumab in different HER2-positive breast carcinoma cells, and is associated with trastuzumab resistance phenotype in vivo in Patient Derived Xenografts. In summary, our data identifies the ERBB2 co-amplified and co-expressed gene GSDMB as a critical determinant of poor prognosis and therapeutic response in HER2-positive breast cancer

Gasdermin B over-expression modulates HER2-targeted therapy resistance by inducing protective autophagy through Rab7 activation

Gasdermin B (GSDMB) over-expression promotes poor prognosis and aggressive behavior in HER2 breast cancer by increasing resistance to therapy. Decoding the molecular mechanism of GSDMB-mediated drug resistance is crucial to identify novel effective targeted treatments for HER2/GSDMB aggressive tumors. Different in vitro approaches (immunoblot, qRT-PCR, flow cytometry, proteomic analysis, immunoprecipitation, and confocal/electron microscopy) were performed in HER2 breast and gastroesophageal carcinoma cell models. Results were then validated using in vivo preclinical animal models and analyzing human breast and gastric cancer samples. GSDMB up-regulation renders HER2 cancer cells more resistant to anti-HER2 agents by promoting protective autophagy. Accordingly, the combination of lapatinib with the autophagy inhibitor chloroquine increases the therapeutic response of GSDMB-positive cancers in vitro and in zebrafish and mice tumor xenograft in vivo models. Mechanistically, GSDMB N-terminal domain interacts with the key components of the autophagy machinery LC3B and Rab7, facilitating the Rab7 activation during pro-survival autophagy in response to anti-HER2 therapies. Finally, we validated these results in clinical samples where GSDMB/Rab7/LC3B co-expression associates significantly with relapse in HER2 breast and gastric cancers. Our findings uncover for the first time a functional link between GSDMB over-expression and protective autophagy in response to HER2-targeted therapies. GSDMB behaves like an autophagy adaptor and plays a pivotal role in modulating autophagosome maturation through Rab7 activation. Finally, our results provide a new and accessible therapeutic approach for HER2/GSDMB + cancers with adverse clinical outcome. The online version contains supplementary material available at 10.1186/s13046-022-02497-w

Human Metastatic Cholangiocarcinoma Patient-Derived Xenografts and Tumoroids for Preclinical Drug Evaluation

Human metastatic cholangiocarcinoma; Xenografts; TumoroidsColangiocarcinoma metastàtic humà; Xenoempelts; TumoroidesColangiocarcinoma metastásico humano; Xenoinjertos; TumoroidesPurpose: Cholangiocarcinoma (CCA) is usually diagnosed at advanced stages, with limited therapeutic options. Preclinical models focused on unresectable metastatic CCA are necessary to develop rational treatments. Pathogenic mutations in IDH1/2, ARID1A/B, BAP1, and BRCA1/2 have been identified in 30%–50% of patients with CCA. Several types of tumor cells harboring these mutations exhibit homologous recombination deficiency (HRD) phenotype with enhanced sensitivity to PARP inhibitors (PARPi). However, PARPi treatment has not yet been tested for effectiveness in patient-derived models of advanced CCA. Experimental Design: We have established a collection of patient-derived xenografts from patients with unresectable metastatic CCA (CCA_PDX). The CCA_PDXs were characterized at both histopathologic and genomic levels. We optimized a protocol to generate CCA tumoroids from CCA_PDXs. We tested the effects of PARPis in both CCA tumoroids and CCA_PDXs. Finally, we used the RAD51 assay to evaluate the HRD status of CCA tissues. Results: This collection of CCA_PDXs recapitulates the histopathologic and molecular features of their original tumors. PARPi treatments inhibited the growth of CCA tumoroids and CCA_PDXs with pathogenic mutations of BRCA2, but not those with mutations of IDH1, ARID1A, or BAP1. In line with these findings, only CCA_PDX and CCA patient biopsy samples with mutations of BRCA2 showed RAD51 scores compatible with HRD. Conclusions: Our results suggest that patients with advanced CCA with pathogenic mutations of BRCA2, but not those with mutations of IDH1, ARID1A, or BAP1, are likely to benefit from PARPi therapy. This collection of CCA_PDXs provides new opportunities for evaluating drug response and prioritizing clinical trials.This work was supported by grants from the Fundació Marató TV3 awarded to T. Macarulla, M. Melé, and S. Peiró; BeiGene research grant awarded to T. Macarulla and S. Peiró; AECC (INVES20036TIAN), Ramón y Cajal investigator program (RYC2020-029098-I), Proyecto de I+D+i (PID2019-108008RJ-I00), and FERO Foundation grant awarded to T.V. Tian; Proyecto de Investigación en Salud from the Instituto de Salud Carlos III (ISCIII) (PI20/00898) awarded to T. Macarulla; FIS/FEDER from the Instituto de Salud Carlos III (ISCIII) (PI12/01250; CP08/00223; PI16/00253 and CB16/12/00449) awarded to S. Peiró; and Ramón y Cajal investigator program (RYC-2017-22249) awarded to M. Melé. Q. Serra-Camprubí is a recipient of the Ph.D. fellowship from La Caixa Foundation (LCF/PR/PR12/51070001). A. Llop-Guevara was supported by the AECC (INVES20095LLOP) and V. Serra by the ISCIII (CPII19/00033). E.J. Arenas was funded by the AECC (POSTD211413AREN). J. Arribas is funded by the Instituto de Salud Carlos III (AC15/00062, CB16/12/00449, and PI22/00001). This publication is based upon the work of COST Action CA18122, European Cholangiocarcinoma Network, supported by the COST (European Cooperation in Science and Technology, www.cost.eu), a funding agency for research and innovation networks. The authors would like to thank Dr. V.A. Raker for manuscript editing and Drs. N. Herranz and J. Mateo for scientific discussions. The authors acknowledge the infrastructure and support of the FERO Foundation, La Caixa Foundation, and the Cellex Foundation

Mechanisms behind the oncogene-induced senescence (OIS) – oncogene-induced apoptosis (OIA) decision in cells expressing p95HER2

[cat] En resposta a un estrès oncogènic, les cèl·lules activen dos mecanismes de supressió tumoral diferents: senescència induïda per oncogens (oncogene-induced senescence, OIS), que consisteix en una parada terminal de la proliferació cel·lular, o apoptosis induïda per oncogens (oncogene-induced apoptosis, OIA), que porta a la desintegració cel·lular. Hem mostrat que l’oncogen p95HER2-611 indueix OIS i que les cèl·lules senescents augmenten la capacitat de metastatitzar de cèl·lules veïnes de càncer de mama amb capacitat proliferant. D’altra banda, es disposa d’evidències que indiquen que la OIA no té aquest efecte secundari indesitjat. Els mecanismes pels quals un insult oncogènic resulta en OIS o en OIA estan poc caracteritzats. En aquest treball ens encarreguem de la caracterització funcional i del mecanisme d’activació d’un altre fragment p95HER2 prèviament descrit, però no caracteritzat, p95HER2-648. Mostrem que l’expressió de p95HER2-648 no porta a senescència sinó a apoptosis. Resultats in vivo mostren que cèl·lules induïdes a senescència per p95HER2-611 afavoreixen la capacitat metastàtica de cèl·lules MDA-MB-231, mentre que cèl·lules induïdes a apoptosis per p95HER2-648 no tenen aquest efecte. Hem observat que cèl·lules expressant p95HER2-611 semblen estar protegides de l’apoptosi. De manera consistent, cèl·lules p95HER2-611 mostren elevats nivells de p21, una proteïna ben coneguda per ser reguladora del cicle cel·lular així com repressora d’apoptosis. La supressió de p21 en aquestes cèl·lules mostra un augment de l’apoptosi indicant que p21 protegeix les cèl·lules senescents contra l’apoptosi. En conclusió, l’expressió dels diferents fragments actius de p95HER2 pot portat tant a apoptosis com a senescència, indicant que la senyalització de HER2 pot induir ambdues respostes depenent de les vies de senyalització activades. Elucidar el mecanisme complert pel qual aquestes dues vies s’activen podria ajudar a trobar una manera de promoure apoptosis en cèl·lules senescents i evitar així els efectes pro-metastàtics.[eng] In response to oncogenic stresses cells activate two different tumor suppressor mechanisms: Oncogene-induced senescence (OIS), a terminal cell proliferation arrest, or oncogene-induced apoptosis (OIA), which leads to cell disintegration. We have shown that the oncogene p95HER2-611 leads cells to OIS and that senescent cells increase the ability of neighbor proliferating breast cancer cells to metastatize. In contrast, available evidence indicates that OIA does not have this undesirable side effect. The mechanisms by which an oncogenic insult results in OIS or OIA remains poorly characterized. In this work, we addressed the functional characterization and the mechanism of activation of another previously described, but uncharacterized, p95HER2 fragment, the p95HER2-648. We showed that the expression of p95HER2-648 does not lead to senescence but to apoptosis. In vivo data showed that p95HER2611-induced senescent cells favor the metastatic capability of MDA-MB-231 cells while p95HER2-648-induced apoptotic cells do not have this effect. We observed that cells bearing p95HER2-611 seem to be protected from apoptosis. Consistently, cells expressing p95HER2-611 showed increased levels of p21, a well-known cell cycle regulator and also an apoptotic repressor. Knock-down of p21 in these cells showed increased apoptosis indicating that p21 is protecting senescent cells against apoptosis. We conclude that the expression of different active p95HER2 fragments can lead to either apoptosis or senescence, indicating that HER2 signaling can induce both cellular responses depending on the activated pathways. Elucidating the complete mechanism by which these pathways are activated could help to find a way to promote apoptosis on senescent cells, in order to avoid their pro-metastatic effect.[spa] En respuesta a un estrés oncogénico, las células activan dos mecanismos de supresión tumoral distintos: Senescencia inducida por oncogenes (oncogene-induced senescence, OIS), que consiste en una parada terminal de la proliferación celular, o apoptosis inducida por oncogenes (oncogene-induced apoptosis, OIA), que lleva a la desintegración celular. Hemos mostrado que el oncogen p95HER2-611 induce OIS y que las células senescentes aumentan la capacidad de metastatizar de células vecinas de cáncer de mama con capacidad proliferante. Por otro lado, se dispone de evidencias que indican que la OIA no tiene este efecto secundario indeseado. Los mecanismos por los cuales un insulto oncogénico resulta en OIS o en OIA están poco caracterizados. En este trabajo, nos encargamos de la caracterización funcional y del mecanismo de activación de otro fragmento p95HER2 previamente descrito, pero no caracterizado, p95HER2-648. Mostramos que la expresión de p95HER2-648 no lleva a senescencia sino a apoptosis. Resultados in vivo muestran que células inducidas a senescencia por p95HER2-611 favorecen la capacidad metastática de las células MDA-MB-231, mientras que células inducidas a apoptosis por p95HER2-648 no tienen este efecto. Hemos observado que células expresando p95HER2-611 parecen estar protegidas de la apoptosis. De forma consistente, células p95HER2-611 muestran elevados niveles de p21, una proteína bien conocida por ser reguladora del ciclo celular así como represora de apoptosis. La supresión de p21 en estas células muestra un aumento de la apoptosis indicando que p21 protege las células senescentes contra la apoptosis. En conclusión, la expresión de los distintos fragmentos activos de p95HER2 puede llevar tanto a apoptosis como a senescencia, indicando que la señalización de HER2 puede inducir las dos respuestas celulares dependiendo de las vías de señalización activadas. Elucidar el mecanismo completo por el cual estas dos vías se activan podría ayudar a encontrar una forma de promover apoptosis en células senescentes y evitar así los efectos pro-metastáticos

Modeling anti-IL-6 therapy using breast cancer patient-derived xenografts

The pleiotropic cytokine IL-6 accelerates the progression of breast cancer in a variety of preclinical models through the activation of the STAT3 (signal transducer and activator of transcription 3) signaling pathway. However, the proportion of breast cancers sensitive to anti-IL-6 therapies is not known. This study evaluates the efficacy of anti-IL-6 therapies using breast cancer patient derived xenografts (PDXs). During the generation of our collection of PDXs, we showed that the successful engraftment of tumor tissue in immunodeficient mice correlates with bad prognosis. Four PDXs out of six were resistant to anti-IL-6 therapies and the expression of IL-6, its receptor or the levels of phospho-STAT3 (the active form of the signal transducer) did not correlate with sensitivity. Using cell cultures established from the PDXs as well as samples from in vivo treatments, we showed that only tumors in which the activation of STAT3 depends on IL-6 respond to the blocking antibodies. Our results indicate that only a fraction of breast tumors are responsive to anti-IL-6 therapies. In order to identify responsive tumors, a functional assay to determine the dependence of STAT3 activation on IL-6 should be performed