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The majority of lung cancer patients progressing from conventional therapies are refractory to PD‐L1/PD‐1 blockade monotherapy. Here, we show that baseline systemic CD4 immunity is a differential factor for clinical responses. Patients with functional systemic CD4 T cells included all objective responders and could be identified before the start of therapy by having a high proportion of memory CD4 T cells. In these patients, CD4 T cells possessed significant proliferative capacities, low co‐expression of PD‐1/LAG‐3 and were responsive to PD‐1 blockade ex vivo and in vivo . In contrast, patients with dysfunctional systemic CD4 immunity did not respond even though they had lung cancer‐specific T cells. Although proficient in cytokine production, CD4 T cells in these patients proliferated very poorly, strongly co‐upregulated PD‐1/LAG‐3, and were largely refractory to PD‐1 monoblockade. CD8 immunity only recovered in patients with functional CD4 immunity. T‐cell proliferative dysfunctionality could be reverted by PD‐1/LAG‐3 co‐blockade. Patients with functional CD4 immunity and PD‐L1 tumor positivity exhibited response rates of 70%, highlighting the contribution of CD4 immunity for efficacious PD‐L1/PD‐1 blockade therapy. Synopsis Lung cancer patients are often refractory to PD‐L1/PD‐1 blockade therapy. This study shows that patients progressing from conventional therapies that have functional CD4 T cells respond to PD‐L1/PD‐1 blockade immunotherapy, while patients with proliferative dysfunctional CD4 T cells do not respond. Functional systemic CD4 immunity is required for objective clinical responses to PD‐L1/PD‐1 blockade therapy in human lung cancer patients. Systemic memory CD4 T cells identify intrinsic non‐responder from potentially responder patients. 70% of patients with high baseline percentages of memory CD4 T cells and PD‐L1‐positive tumors respond to therapy. Proliferative CD4 dysfunctionality in non‐responder patients can be overcome by PD‐1/LAG‐3 co‐blockade. Graphical Abstract Lung cancer patients are often refractory to PD‐L1/PD‐1 blockade therapy. This study shows that patients progressing from conventional therapies that have functional CD4 T cells respond to PD‐L1/PD‐1 blockade immunotherapy, while patients with proliferative dysfunctional CD4 T cells do not respond.

In the context of tumorigenesis, telomere shortening is associated with apparent antagonistic outcomes: On one side, it favors cancer initiation through mechanisms involving genome instability, while on the other side, it prevents cancer progression, due to the activation of the DNA damage response (DDR) checkpoint behaving as a cell‐intrinsic proliferation barrier. Consequently, telomerase, which can compensate for replicative erosion by adding telomeric DNA repeats at the chromosomal DNA extremities, is crucial for cancer progression and is upregulated in nearly 90% of human cancers. Therefore, telomeres are considered potential anti‐cancer targets and, to date, most of the studies have focused on telomerase inhibition. However, the development of clinically efficient telomerase targeting therapies is still in its infancy. In this context, the findings reported in this issue of EMBO Molecular Medicine by Bejarano et al (2019) open new avenues for alternative telomere therapies. Graphical Abstract J. Cherfils‐Vicini and E. Gilson discuss the findings by Bejanaro et al (in this issue of EMBO Molecular Medicine ) that report targeting of the telomeric shelterin complex via FDA approved drugs that inhibit TRF1.

Understanding the mechanisms underlying evasive resistance in cancer is an unmet medical need to improve the efficacy of current therapies. In this study, a combination of shRNA‐mediated synthetic lethality screening and transcriptomic analysis revealed the transcription factors YAP/TAZ as key drivers of Sorafenib resistance in hepatocellular carcinoma (HCC) by repressing Sorafenib‐induced ferroptosis. Mechanistically, in a TEAD‐dependent manner, YAP/TAZ induce the expression of SLC7A11, a key transporter maintaining intracellular glutathione homeostasis, thus enabling HCC cells to overcome Sorafenib‐induced ferroptosis. At the same time, YAP/TAZ sustain the protein stability, nuclear localization, and transcriptional activity of ATF4 which in turn cooperates to induce SLC7A11 expression. Our study uncovers a critical role of YAP/TAZ in the repression of ferroptosis and thus in the establishment of Sorafenib resistance in HCC, highlighting YAP/TAZ‐based rewiring strategies as potential approaches to overcome HCC therapy resistance. SYNOPSIS Resistance to therapy occurs in most liver cancer patients treated with Sorafenib, and patients succumb to the disease. A synthetic lethal screen identified a regulatory circuit, which prevents ferroptosis and promotes cancer cell survival, thus promoting resistance to Sorafenib. The transcription factors YAP and TAZ stabilize ATF4 by promoting its nuclear import to cooperatively induce expression of SLC7A11, a cystine importer critical for glutathione synthesis. Glutathione synthesis and homeostasis are required to repress ferroptosis and to maintain Sorafenib resistance in liver cancer cells. Inhibition of Glutathione synthesis re‐sensitizes Sorafenib‐resistant cancer cells to Sorafenib therapy, which then induces ferroptosis and represses tumor growth in murine liver cancer models. Pharmacological repression of the anti‐oxidant pathways regulated by YAP/TAZ and ATF4 could re‐sensitize therapy‐resistant liver cancers to Sorafenib treatment. Graphical Abstract Resistance to therapy occurs in most liver cancer patients treated with Sorafenib, and patients succumb to the disease. A synthetic lethal screen identified a regulatory circuit, which prevents ferroptosis and promotes cancer cell survival, thus promoting resistance to Sorafenib.

Sarcomas are heterogeneous and clinically challenging soft tissue and bone cancers. Although constituting only 1% of all human malignancies, sarcomas represent the second most common type of solid tumors in children and adolescents and comprise an important group of secondary malignancies. More than 100 histological subtypes have been characterized to date, and many more are being discovered due to molecular profiling. Owing to their mostly aggressive biological behavior, relative rarity, and occurrence at virtually every anatomical site, many sarcoma subtypes are in particular difficult‐to‐treat categories. Current multimodal treatment concepts combine surgery, polychemotherapy (with/without local hyperthermia), irradiation, immunotherapy, and/or targeted therapeutics. Recent scientific advancements have enabled a more precise molecular characterization of sarcoma subtypes and revealed novel therapeutic targets and prognostic/predictive biomarkers. This review aims at providing a comprehensive overview of the latest advances in the molecular biology of sarcomas and their effects on clinical oncology; it is meant for a broad readership ranging from novices to experts in the field of sarcoma. Graphical Abstract Sarcomas are heterogeneous and clinically challenging soft tissue and bone cancers. The current article comprehensively reviews recent advances in the molecular characterization of sarcoma subtypes, and describes novel therapeutic targets and biomarkers in this field.

Tumor‐associated macrophages (TAMs) promote tumor growth and metastasis by suppressing tumor immune surveillance. Herein, we provide evidence that the immunosuppressive phenotype of TAMs is controlled by long‐chain fatty acid metabolism, specifically unsaturated fatty acids, here exemplified by oleate. Consequently, en‐route enriched lipid droplets were identified as essential organelles, which represent effective targets for chemical inhibitors to block in vitro polarization of TAMs and tumor growth in vivo . In line, analysis of human tumors revealed that myeloid cells infiltrating colon cancer but not gastric cancer tissue indeed accumulate lipid droplets. Mechanistically, our data indicate that oleate‐induced polarization of myeloid cells depends on the mammalian target of the rapamycin pathway. Thus, our findings reveal an alternative therapeutic strategy by targeting the pro‐tumoral myeloid cells on a metabolic level. Synopsis Tumor‐associated macrophages (TAMs) are the main regulatory cell type in the tumor stroma as well as the microenvironment. This study describes how fatty acids polarize myeloid cells to TAMs and how this polarization is controlled by lipid droplet‐dependent fatty acid metabolism. The fatty acid‐enriched tumor environment itself was sufficient to induce the regulatory phenotype of TAMs, including the up‐regulation of classical markers like CD206, IL‐6, VEGFα, MMP9 or Arg1. The fatty acid‐induced TAM polarization was lipid droplet dependent. mTORC2 activation played a critical role in the generation of the suppressive myeloid cell phenotype. Cell‐specific inhibition of DGAT1 and 2 prevented oleate‐induced polarization into immunosuppressive TAMs in vitro in murine and human cell culture systems as well as in vivo in a murine tumor model. Graphical Abstract Tumor‐associated macrophages (TAMs) are the main regulatory cell type in the tumor stroma as well as the microenvironment. This study describes how fatty acids polarize myeloid cells to TAMs and how this polarization is controlled by lipid droplet‐dependent fatty acid metabolism.

Metastasis is a major cause of morbidity and mortality in cancer patients. However, the molecular and cellular mechanisms underlying the ability of cancer cells to metastasize remain relatively poorly understood. Among all solid tumors, small cell lung cancer (SCLC) has remarkable metastatic proclivity, with a majority of patients diagnosed with metastatic disease. Our understanding of SCLC metastasis has been hampered for many years by the paucity of material from primary tumors and metastases, as well as the lack of faithful pre‐clinical models. Here, we review recent advances that are helping circumvent these limitations. These advances include methods that employ circulating tumor cells from the blood of SCLC patients and the development of diverse genetically engineered mouse models of metastatic SCLC. New insights into the cellular mechanisms of SCLC metastasis include observations of cell fate changes associated with increased metastatic ability. Ongoing studies on cell migration and organ tropism promise to expand our understanding of SCLC metastasis. Ultimately, a better molecular understanding of metastatic phenotypes may be translated into new therapeutic options to limit metastatic spread and treat metastatic SCLC. Graphical Abstract Small cell lung cancer (SCLC) is highly metastatic, but rare resections of SCLC tumors and metastases have hampered our understanding of SCLC progression. This review offers a comprehensive overview of recent advances on models and mechanisms of SCLC metastasis.

Poly(ADP‐ribose) polymerase (PARP) inhibitors (PARPi) are effective in cancers with defective homologous recombination DNA repair (HRR), including BRCA1/2‐related cancers. A test to identify additional HRR‐deficient tumors will help to extend their use in new indications. We evaluated the activity of the PARPi olaparib in patient‐derived tumor xenografts (PDXs) from breast cancer (BC) patients and investigated mechanisms of sensitivity through exome sequencing, BRCA1 promoter methylation analysis, and immunostaining of HRR proteins, including RAD51 nuclear foci. In an independent BC PDX panel, the predictive capacity of the RAD51 score and the homologous recombination deficiency (HRD) score were compared. To examine the clinical feasibility of the RAD51 assay, we scored archival breast tumor samples, including PALB2‐related hereditary cancers. The RAD51 score was highly discriminative of PARPi sensitivity versus PARPi resistance in BC PDXs and outperformed the genomic test. In clinical samples, all PALB2‐related tumors were classified as HRR‐deficient by the RAD51 score. The functional biomarker RAD51 enables the identification of PARPi‐sensitive BC and broadens the population who may benefit from this therapy beyond BRCA1/2‐related cancers. Synopsis Sensitive and highly specific biomarkers usable in archived formalin fixed parafin embedded (FFPE) tumour samples are needed to extend the use of PARP inhibitors beyond BRCA1/2‐related cancers. The RAD51 score may satisfy this clinical unmet need. The RAD51 score shows complete discriminative capacity in predicting PARP inhibitor response. The RAD51 score is feasible in routine breast tumor samples without prior exposure to DNA damaging agents. Carrying a PALB2 mutation is associated with a low RAD51score. Graphical Abstract Sensitive and highly specific biomarkers usable in archived formalin fixed parafin embedded (FFPE) tumour samples are needed to extend the use of PARP inhibitors beyond BRCA1/2‐related cancers. The RAD51 score may satisfy this clinical unmet need.

Chimeric antigen receptor (CAR) T cell therapy, together with checkpoint inhibition, has been celebrated as a breakthrough technology due to the substantial benefit observed in clinical trials with patients suffering from relapsed or refractory B‐cell malignancies. In this review, we provide a comprehensive overview of the clinical trials performed so far worldwide and analyze parameters such as targeted antigen and indication, CAR molecular design, CAR T cell manufacturing, anti‐tumor activities, and related toxicities. More than 200 CAR T cell clinical trials have been initiated so far, most of which aim to treat lymphoma or leukemia patients using CD19‐specific CARs. An increasing number of studies address solid tumors as well. Notably, not all clinical trials conducted so far have shown promising results. Indeed, in a few patients CAR T cell therapy resulted in severe adverse events with fatal outcome. Of note, less than 10% of the ongoing CAR T cell clinical trials are performed in Europe. Taking lead from our analysis, we discuss the problems and general hurdles preventing efficient clinical development of CAR T cells as well as opportunities, with a special focus on the European stage. Graphical Abstract Authoritative, insightful overview of the problems and general hurdles preventing efficient clinical development of chimeric antigen receptor (CAR) T cell therapy for cancer as well as future opportunities.

Malignant cell growth is fueled by interactions between tumor cells and the stromal cells composing the tumor microenvironment. The human liver is a major site of tumors and metastases, but molecular identities and intercellular interactions of different cell types have not been resolved in these pathologies. Here, we apply single cell RNA‐sequencing and spatial analysis of malignant and adjacent non‐malignant liver tissues from five patients with cholangiocarcinoma or liver metastases. We find that stromal cells exhibit recurring, patient‐independent expression programs, and reconstruct a ligand–receptor map that highlights recurring tumor–stroma interactions. By combining transcriptomics of laser‐capture microdissected regions, we reconstruct a zonation atlas of hepatocytes in the non‐malignant sites and characterize the spatial distribution of each cell type across the tumor microenvironment. Our analysis provides a resource for understanding human liver malignancies and may expose potential points of interventions. SYNOPSIS Single cell transcriptomics and spatial methods are used to generate a cell atlas of the human liver tumor microenvironment, exposing recurring tumor‐stroma interactions and zonation patterns in the healthy and malignant tissue. A single cell atlas of the malignant and adjacent non‐malignant human liver is presented. Recurring stromal cell gene expression signatures are found in liver metastases and cholangiocarcinomas. Tumor and stromal cells communicate through a conserved ligand‐receptor interaction network. Spatial transcriptomics reveal zonated expression patterns in the malignant and non‐malignant liver. Graphical Abstract Single cell transcriptomics and spatial methods are used to generate a cell atlas of the human liver tumor microenvironment, exposing recurring tumor‐stroma interactions and zonation patterns in the healthy and malignant tissue.

In colorectal cancer, oncogenic mutations transform a hierarchically organized and homeostatic epithelium into invasive cancer tissue lacking visible organization. We sought to define transcriptional states of colorectal cancer cells and signals controlling their development by performing single‐cell transcriptome analysis of tumors and matched non‐cancerous tissues of twelve colorectal cancer patients. We defined patient‐overarching colorectal cancer cell clusters characterized by differential activities of oncogenic signaling pathways such as mitogen‐activated protein kinase and oncogenic traits such as replication stress. RNA metabolic labeling and assessment of RNA velocity in patient‐derived organoids revealed developmental trajectories of colorectal cancer cells organized along a mitogen‐activated protein kinase activity gradient. This was in contrast to normal colon organoid cells developing along graded Wnt activity. Experimental targeting of EGFR‐BRAF‐MEK in cancer organoids affected signaling and gene expression contingent on predictive KRAS/BRAF mutations and induced cell plasticity overriding default developmental trajectories. Our results highlight directional cancer cell development as a driver of non‐genetic cancer cell heterogeneity and re‐routing of trajectories as a response to targeted therapy. SYNOPSIS Colorectal cancer (CRC) cells can adopt a range of transcriptomic states. This study uses single cell RNA sequencing of primary CRC tissue and organoids to identify patient‐overarching CRC cell transcriptome clusters. RNA metabolic labelling indicates preferred CRC cell developmental trajectories. CRC cells of multiple patients clustered into six groups – termed TC1‐4, Goblet‐like, and stem‐like – characterized by differential transcriptional footprints of oncogenic signaling pathways. CRC organoid cells develop along a decreasing MAPK gradient. Experimental targeting of EGFR‐MAPK in CRC organoids re‐routes developmental trajectories. Clinically relevant inhibition of EGFR‐MAPK can result in preferential CRC cell development towards endpoints expressing high levels of stem cell markers. Graphical Abstract Colorectal cancer (CRC) cells can adopt a range of transcriptomic states. This study uses single cell RNA sequencing of primary CRC tissue and organoids to identify patient‐overarching CRC cell transcriptome clusters. RNA metabolic labelling indicates preferred CRC cell developmental trajectories.