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Peritoneal metastases are a common form of tumor cell dissemination in gastrointestinal malignancies. Peritoneal metastatic disease (PMD) is associated with severe morbidity and resistance to currently employed therapies. Given the distinct route of dissemination compared with distant organ metastases, and the unique microenvironment of the peritoneal cavity, specific tumor cell characteristics are needed for the development of PMD. In this review, we provide an overview of the known histopathological, genomic, and transcriptomic features of PMD. We find that cancers representing the mesenchymal subtype are strongly associated with PMD in various malignancies. Furthermore, we discuss the peritoneal niche in which the metastatic cancer cells reside, including the critical role of the peritoneal immune system. Altogether, we show that PMD should be regarded as a distinct disease entity, that requires tailored treatment strategies. Graphical Abstract In this review, S. Bootsma, M. Bijlsma, and L. Vermeulen provide an overview of the histopathological, genomic, and transcriptomic features of peritoneal metastases and argue that peritoneal metastatic disease should be considered a distinct disease entity.

Pancreatic ductal adenocarcinoma (PDAC) remains one of the most aggressive malignancies to date, largely because it is associated with high metastatic risk. Pancreatic tumors have a characteristic tendency to metastasize preferentially to the liver. Over the past two decades, it has become evident that the otherwise hostile milieu of the liver is selectively preconditioned at an early stage to render it more conducive to the engraftment and growth of disseminated cancer cells, a concept defined as pre-metastatic niche (PMN) formation. Pancreatic cancer cells exploit components of the tumor microenvironment to facilitate their migration out of the primary tumor, which often involves conversion of pancreatic cancer cells from an epithelial to a mesenchymal phenotype via the epithelial-to-mesenchymal transition. Pancreatic stellate cells and matrix stiffness have been put forward as major drivers of invasiveness in PDAC. Even before the onset of pancreatic cancer cell dissemination, soluble factors and extracellular vesicles secreted by the primary tumor, and possibly even premalignant lesions, help shape a supportive niche in the liver by providing vascular docking sites for circulating tumor cells, enhancing vascular permeability, remodeling the extracellular matrix and recruiting immunosuppressive inflammatory cells. Emerging evidence suggests that some of these tumor-derived factors may represent powerful diagnostic or prognostic biomarkers. Though our understanding of the mechanisms driving PMN formation in PDAC has expanded considerably, many outstanding questions and challenges remain. Further studies dissecting the molecular and cellular events involved in hepatic PMN formation in PDAC will likely improve diagnosis and open new avenues from a therapeutic standpoint.

Analysis of gene-expression profiles led to the identification of three molecularly distinct subtypes of colon cancer. One of these subtypes is new, and its identification is of clinical interest because it tends to have a particularly unfavorable prognosis and is refractory to existing targeted therapies. Colon cancer is a clinically diverse disease. This heterogeneity makes it difficult to determine which patients will benefit most from adjuvant therapy and impedes the development of new targeted agents 1 . More insight into the biological diversity of colon cancers, especially in relation to clinical features, is therefore needed. We demonstrate, using an unsupervised classification strategy involving over 1,100 individuals with colon cancer, that three main molecularly distinct subtypes can be recognized. Two subtypes have been previously identified and are well characterized (chromosomal-instable and microsatellite-instable cancers) 2 . The third subtype is largely microsatellite stable and contains relatively more CpG island methylator phenotype–positive carcinomas but cannot be identified on the basis of characteristic mutations. We provide evidence that this subtype relates to sessile-serrated adenomas, which show highly similar gene expression profiles, including upregulation of genes involved in matrix remodeling and epithelial-mesenchymal transition. The identification of this subtype is crucial, as it has a very unfavorable prognosis and, moreover, is refractory to epidermal growth factor receptor–targeted therapy.

Background Pancreatic ductal adenocarcinoma (PDAC) is a grim disease with high mortality rates. Increased macrophage influx in PDAC is a common hallmark and associated with poor prognosis. Macrophages have high cellular plasticity, which can differentiate into both anti- and pro-tumorigenic properties. Here, we investigated how naïve (M0) macrophages differ from other macrophages in their anti-tumorigenic activities. Methods In vitro BrdU proliferation and Annexin V cell death analyses were performed on PANC-1 and MIA PaCa-2 PDAC cell lines exposed to conditioned medium of different macrophage subsets. Macrophage secreted factors were measured by transcript analysis and ELISA. Therapeutic antibodies were used to functionally establish the impact of the identified cytokine on PDAC proliferation. Results Proliferation and cell death assays revealed that only M0 macrophages harbor anti-tumorigenic activities and that M1, M2, and TAMs do not. mRNA analysis and ELISA results suggested TNF-α as a potential candidate to mediate M0 macrophage induced cell death. To demonstrate the importance of TNF-α in M0 macrophage-induced cell death, PANC-1 and MIA PaCa-2 cell-lines were exposed to M0 macrophage conditioned medium in the presence of the TNF-α inhibitor Infliximab, which effectively diminished the anti-tumor activities of M0 macrophages. Conclusion Newly tumor-infiltrated naive M0 macrophages exert anti-tumorigenic activities via TNF-α secretion. Their subsequent differentiation into either M1, M2, or TAM subsets reduces TNF-α levels, thereby abolishing their cytotoxic activity on PDAC cells. These data suggest that reestablishing TNF-α secretion in differentiated macrophages might yield a therapeutic benefit.

Pancreatic cancer is a dismal disorder that is histologically characterized by a dense fibrotic stroma around the tumor cells. As the extracellular matrix comprises the bulk of the stroma, matrix degrading proteases may play an important role in pancreatic cancer. It has been suggested that matrix metalloproteases are key drivers of both tumor growth and metastasis during pancreatic cancer progression. Based upon this notion, changes in matrix metalloprotease expression levels are often considered surrogate markers for pancreatic cancer progression and/or treatment response. Indeed, reduced matrix metalloprotease levels upon treatment (either pharmacological or due to genetic ablation) are considered as proof of the anti-tumorigenic potential of the mediator under study. In the current review, we aim to establish whether matrix metalloproteases indeed drive pancreatic cancer progression and whether decreased matrix metalloprotease levels in experimental settings are therefore indicative of treatment response. After a systematic review of the studies focusing on matrix metalloproteases in pancreatic cancer, we conclude that the available literature is not as convincing as expected and that, although individual matrix metalloproteases may contribute to pancreatic cancer growth and metastasis, this does not support the generalized notion that matrix metalloproteases drive pancreatic ductal adenocarcinoma progression.

BackgroundThe COVID-19 pandemic has affected the entire global healthcare system, including oncological care. This study investigated the effects of the COVID-19 pandemic on the diagnosis, stage, and treatment of esophagogastric cancer in the Netherlands.MethodsPatients diagnosed in 2020 were divided into 5 periods, based on the severity of the COVID-19 pandemic in the Netherlands, and compared to patients diagnosed in the same period in the years 2017–2019. Patient characteristics and treatments were evaluated for esophageal cancer (EC) and gastric cancer (GC) separately.ResultsThe number of esophagogastric cancer diagnoses decreased prominently during the first 2 months of the COVID-19 pandemic. During this period, a significantly higher percentage of GC patients was diagnosed with incurable disease (52.5% in 2017–2019 and 67.7% in 2020, p = 0.011). We observed a significant reduction in the percentage of patients with potentially curable EC treated with resection and neoadjuvant chemoradiotherapy (from 35.0% in 2017–2019 to 27.3% in 2020, p < 0.001). Also, patients diagnosed with incurable GC were treated less frequently with a resection (from 4.6% in 2017–2019 to 1.5% in 2020, p = 0.009) in the second half of 2020.ConclusionsCompared to previous years, the number of esophagogastric cancer diagnoses decreased in the first 2 months of the COVID-19 pandemic, while an increased percentage of patients was diagnosed with incurable disease. Both in the curative and palliative setting, patients were less likely to be treated with a surgical resection.

Cancer evolution is predominantly studied by focusing on differences in the genetic characteristics of malignant cells within tumors. However, the spatiotemporal dynamics of clonal outgrowth that underlie evolutionary trajectories remain largely unresolved. Here, we sought to unravel the clonal dynamics of colorectal cancer (CRC) expansion in space and time by using a color-based clonal tracing method. This method involves lentiviral red-green-blue (RGB) marking of cell populations, which enabled us to track individual cells and their clonal outgrowth during tumor initiation and growth in a xenograft model. We found that clonal expansion largely depends on the location of a clone, as small clones reside in the center and large clones mostly drive tumor growth at the border. These dynamics are recapitulated in a computational model, which confirms that the clone position within a tumor rather than cell-intrinsic features, is crucial for clonal outgrowth. We also found that no significant clonal loss occurs during tumor growth and clonal dispersal is limited in most models. Our results imply that, in addition to molecular features of clones such as (epi-)genetic differences between cells, clone location and the geometry of tumor growth are crucial for clonal expansion. Our findings suggest that either microenvironmental signals on the tumor border or differences in physical properties within the tumor, are major contributors to explain heterogeneous clonal expansion. Thus, this study provides further insights into the dynamics of solid tumor growth and progression, as well as the origins of tumor cell heterogeneity in a relevant model system.

Ovarian cancer is the deadliest gynecological malignancy, with high relapse and drug resistance rates. Hyperthermic intraperitoneal chemotherapy (HIPEC) combined with cytoreductive surgery and systemic chemotherapy has improved survival in patients with peritoneal metastases, though findings remain inconsistent. This study investigates whether the benefits of HIPEC are due to the additional chemotherapy or the combination with hyperthermia. High-grade and non-high-grade serous ovarian cancer cell lines were treated with carboplatin and paclitaxel. Additionally, the cells were treated with cisplatin at 37 to 43 °C for 90 min (HIPEC). Cell proliferation, colony formation, apoptosis, cell cycle and DNA damage were assessed by MTT, clonogenic assay, flow cytometry, western blot and γ-H2AX foci assay. High-grade serous cells were more sensitive to both carboplatin-paclitaxel and hyperthermia. Cisplatin demonstrated a temperature-dependent synergy with heat, resulting in increased DNA damage, apoptosis, and G2-arrest. Combining carboplatin and paclitaxel with hyperthermia plus cisplatin further reduced survival and increased cellular stress marker compared to carboplatin and paclitaxel alone. Hyperthermia significantly enhances cisplatin efficacy when added to carboplatin and paclitaxel pretreatment. This suggests that the addition of hyperthermia to cisplatin after carboplatin-paclitaxel is more effective than carboplatin-paclitaxel alone in both high-grade and non-high grade serous ovarian cancer.

Abtract In cancer, mitochondrial fission and fusion dynamics are often imbalanced due to altered transcriptional and post-transcriptional control of their key regulators, resulting in either excessive fission or fusion. Despite being opposing processes, these imbalances in mitochondrial dynamics play a critical role in tumorigenic processes. Excessive fission drives metabolic reprogramming by promoting a shift toward aerobic glycolysis and regulating fatty acid metabolism, whereas excessive fusion supports oxidative phosphorylation and glutaminolysis. Both processes, in their own specific way, enable rapid growth and enhance survival in heterogeneous and unfavorable tumor microenvironments. Beyond metabolic regulation, excessive fission plays a key role in invasion and metastasis by promoting cytoskeletal remodeling for single-cell migration and inducing epithelial-to-mesenchymal transition. Moreover, both excessive fission and fusion can inhibit apoptosis and enhance therapy resistance by modulation of the intrinsic apoptosis pathway, upregulation of antioxidant defenses, and/or activation of autophagy. This review examines how both dysregulated fission and fusion contribute to tumorigenic processes in solid tumors and highlights mitochondrial dynamics as a promising therapeutic target.

Despite recent advances in cancer immunotherapy, pancreatic ductal adenocarcinoma (PDAC) remains unresponsive due to an immunosuppressive tumor microenvironment, which is characterized by the abundance of cancer-associated fibroblasts (CAFs). Once identified, CAF-mediated immune inhibitory mechanisms could be exploited for cancer immunotherapy. Siglec receptors are increasingly recognized as immune checkpoints, and their ligands, sialic acids, are known to be overexpressed by cancer cells. Here, we unveil a previously unrecognized role of sialic acid-containing glycans on PDAC CAFs as crucial modulators of myeloid cells. Using multiplex immunohistochemistry and transcriptomics, we show that PDAC stroma is enriched in sialic acid-containing glycans compared to tumor cells and normal fibroblasts, and characterized by ST3GAL4 expression. We demonstrate that sialic acids on CAF cell lines serve as ligands for Siglec-7, -9, -10 and -15, distinct from the ligands on tumor cells, and that these receptors are found on myeloid cells in the stroma of PDAC biopsies. Furthermore, we show that CAFs drive the differentiation of monocytes to immunosuppressive tumor-associated macrophages in vitro, and that CAF sialylation plays a dominant role in this process compared to tumor cell sialylation. Collectively, our findings unravel sialic acids as a mechanism of CAF-mediated immunomodulation, which may provide targets for immunotherapy in PDAC. Pancreatic cancer-associated fibroblast enhance the expression of sialic acidcontaining glycans, which interact with Siglec7, -9, -10, -15 receptors on myeloid cells, and drive the differentiation to immunosuppressive macrophages.