Gastric cancer immunosuppressive microenvironment heterogeneity: implications for therapy development.

Although immunotherapy has revolutionized solid tumor treatment, durable responses in gastric cancer (GC) remain limited. The heterogeneous tumor microenvironment (TME) facilitates immune evasion, contributing to resistance to conventional and immune therapies. Recent studies have highlighted how specific TME components in GC acquire immune escape capabilities through cancer-specific factors. Understanding the underlying molecular mechanisms and targeting the immunosuppressive TME will enhance immunotherapy efficacy and patient outcomes. This review summarizes recent advances in GC TME research and explores the role of the immune-suppressive system as a context-specific determinant. We also provide insights into potential treatments beyond checkpoint inhibition.

RAC1-mediated integrin alpha-6 expression in E-cadherin-deficient gastric cancer cells promotes interactions with the stroma and peritoneal dissemination.

Diffuse-type gastric cancer (DGC) is a subtype of gastric cancer that is prone to peritoneal dissemination, with poor patient prognosis. Although intercellular adhesion loss between cancer cells is a major characteristic of DGCs, the mechanism underlying the alteration in cell-to-extracellular matrix (ECM) adhesion is unclear. We investigated how DGCs progress and cause peritoneal dissemination through interactions between DGC cells and the tumour microenvironment (TME). P53 knockout and KRASG12V-expressing (GAN-KP) cells and Cdh1-deleted GAN-KP (GAN-KPC) cells were orthotopically transplanted into the gastric wall to mimic peritoneal dissemination. The GAN-KPC tumour morphology was similar to that of human DGCs containing abundant stroma. RNA sequencing revealed that pathways related to Rho GTPases and integrin-ECM interactions were specifically increased in GAN-KPC cells compared with GAN-KP cells. Notably, we found that Rac Family Small GTPase 1 (RAC1) induces Integrin Subunit Alpha 6 (ITGA6) trafficking, leading to its enrichment on the GC cell membrane. Fibroblasts activate the FAK/AKT pathway in GC cells by mediating extracellular matrix (ECM)-Itga6 interactions, exacerbating the malignant phenotype. In turn, GC cells induce abnormal expression of fibroblast collagen and its transformation into cancer-associated fibroblasts (CAFs), resulting in DGC-like subtypes. These findings indicate that Cdh1 gene loss leads to abnormal expression and changes in the subcellular localization of ITGA6 through RAC1 signalling. The latter, through interactions with CAFs, allows for peritoneal dissemination.

Mesothelial cells with mesenchymal features enhance peritoneal dissemination by forming a protumorigenic microenvironment.

Malignant ascites accompanied by peritoneal dissemination contain various factors and cell populations as well as cancer cells; however, how the tumor microenvironment is shaped in ascites remains unclear. Single-cell proteomic profiling and a comprehensive proteomic analysis are conducted to comprehensively characterize malignant ascites. Here, we find defects in immune effectors along with immunosuppressive cell accumulation in ascites of patients with gastric cancer (GC) and identify five distinct subpopulations of CD45(-)/EpCAM(-) cells. Mesothelial cells with mesenchymal features in CD45(-)/EpCAM(-) cells are the predominant source of chemokines involved in immunosuppressive myeloid cell (IMC) recruitment. Moreover, mesothelial-mesenchymal transition (MMT)-induced mesothelial cells strongly express extracellular matrix (ECM)-related genes, including tenascin-C (TNC), enhancing metastatic colonization. These findings highlight the definite roles of the mesenchymal cell population in the development of a protumorigenic microenvironment to promote peritoneal dissemination.

Downregulation of 15-PGDH enhances MASH-HCC development via fatty acid-induced T-cell exhaustion.

Background & Aims: Hepatocellular carcinoma (HCC) mainly develops from chronic hepatitis. Metabolic dysfunction-associated steatohepatitis (MASH) has gradually become the main pathogenic factor for HCC given the rising incidence of obesity and metabolic diseases. 15-Hydroxyprostaglandin dehydrogenase (15-PGDH) degrades prostaglandin 2 (PGE2), which is known to exacerbate inflammatory responses. However, the role of PGE2 accumulation caused by 15-PGDH downregulation in the development of MASH-HCC has not been determined. Methods: We utilised the steric animal model to establish a MASH-HCC model using wild-type and 15-Pgdh+/- mice to assess the significance of PGE2 accumulation in the development of MASH-HCC. Additionally, we analysed clinical samples obtained from patients with MASH-HCC. Results: PGE2 accumulation in the tumour microenvironment induced the production of reactive oxygen species in macrophages and the expression of cell growth-related genes and antiapoptotic genes. Conversely, the downregulation of fatty acid metabolism in the background liver promoted lipid accumulation in the tumour microenvironment, causing a decrease in mitochondrial membrane potential and CD8+ T-cell exhaustion, which led to enhanced development of MASH-HCC. Conclusions: 15-PGDH downregulation inactivates immune surveillance by promoting the proliferation of exhausted effector T cells, which enhances hepatocyte survival and proliferation and leads to the development of MASH-HCC. Impact and implications: The suppression of PGE2-related inflammation and subsequent lipid accumulation leads to a reduction in the severity of MASH and inhibition of subsequent progression toward MASH-HCC.

Cancer-associated fibroblasts reuse cancer-derived lactate to maintain a fibrotic and immunosuppressive microenvironment in pancreatic cancer.

Glycolysis is highly enhanced in pancreatic ductal adenocarcinoma (PDAC) cells; thus, glucose restrictions are imposed on nontumor cells in the PDAC tumor microenvironment (TME). However, little is known about how such glucose competition alters metabolism and confers phenotypic changes in stromal cells in the TME. Here, we report that cancer-associated fibroblasts (CAFs) with restricted glucose availability utilize lactate from glycolysis-enhanced cancer cells as a fuel and exert immunosuppressive activity in the PDAC TME. The expression of lactate dehydrogenase A (LDHA), which regulates lactate production, was a poor prognostic factor for patients with PDAC, and LDHA depletion suppressed tumor growth in a CAF-rich murine PDAC model. Coculture of CAFs with PDAC cells revealed that most of the glucose was taken up by the tumor cells and that CAFs consumed lactate via monocarboxylate transporter 1 to enhance proliferation through the TCA cycle. Moreover, lactate-stimulated CAFs upregulated IL-6 expression and suppressed cytotoxic immune cell activity synergistically with lactate. Finally, the LDHA inhibitor FX11 reduced tumor growth and improved antitumor immunity in CAF-rich PDAC tumors. Our study provides insight regarding the crosstalk among tumor cells, CAFs, and immune cells mediated by lactate and offers therapeutic strategies for targeting LDHA enzymatic activity in PDAC cells.

Stromal Reprogramming through Dual PDGFRα/ß Blockade Boosts the Efficacy of Anti-PD-1 Immunotherapy in Fibrotic Tumors.

Excess stroma and cancer-associated fibroblasts (CAF) enhance cancer progression and facilitate immune evasion. Insights into the mechanisms by which the stroma manipulates the immune microenvironment could help improve cancer treatment. Here, we aimed to elucidate potential approaches for stromal reprogramming and improved cancer immunotherapy. Platelet-derived growth factor C (PDGFC) and D expression were significantly associated with a poor prognosis in patients with gastric cancer, and PDGF receptor beta (PDGFRß) was predominantly expressed in diffuse-type gastric cancer stroma. CAFs stimulated with PDGFs exhibited markedly increased expression of CXCL1, CXCL3, CXCL5, and CXCL8, which are involved in polymorphonuclear myeloid-derived suppressor cell (PMN-MDSC) recruitment. Fibrotic gastric cancer xenograft tumors exhibited increased PMN-MDSC accumulation and decreased lymphocyte infiltration, as well as resistance to anti-PD-1. Single-cell RNA sequencing and spatial transcriptomics revealed that PDGFRα/ß blockade reversed the immunosuppressive microenvironment through stromal modification. Finally, combining PDGFRα/ß blockade and anti-PD-1 treatment synergistically suppressed the growth of fibrotic tumors. These findings highlight the impact of stromal reprogramming on immune reactivation and the potential for combined immunotherapy for patients with fibrotic cancer. SIGNIFICANCE: Stromal targeting with PDGFRα/ß dual blockade reverses the immunosuppressive microenvironment and enhances the efficacy of immune checkpoint inhibitors in fibrotic cancer. See related commentary by Tauriello, p. 655.

IL-1ß derived from mixed-polarized macrophages activates fibroblasts and synergistically forms a cancer-promoting microenvironment.

BACKGROUND: Remodeling the tumor microenvironment (TME) to benefit cancer cells is crucial for tumor progression. Although diffuse-type gastric cancer (DGC) preferentially interacts with the TME, the precise mechanism of the complicated network remains unknown. This study aimed to investigate the mutual activation mechanism underlying DGC progression. METHODS: Mass cytometry analysis of co-cultured macrophages, noncancerous fibroblasts (NFs), and DGC cells was performed. RNA sequencing was applied to examine gene expression in fibroblasts. DGC cells were treated with cytokines to examine their effect on characteristic changes. The TCGA and Kumamoto University cohorts were used to evaluate the clinical relevance of the in vitro findings. RESULTS: Cohort analysis revealed that DGC patients had a poor prognosis. The fibroblasts and macrophages interacted with DGC cells to form a cell cluster in the invasive front of DGC tissue. The original 3D triple co-culture system determined the promotional effects of nonmalignant cells on DGC invasive growth. We notably identified a mixed-polarized macrophage cell type with M1/M2 cell surface markers in a triple co-culture system. IL-1ß from mixed-polarized macrophages induced the conversion of NFs to cancer-associated fibroblast-like (CAF-like) cells, promoting the malignant phenotype of DGC cells by inducing the secretion of IL-6, IL-24, and leukemia inhibitory factor (LIF). Moreover, IL-6 and colony stimulating factor 2 (GM-CSF) cooperated to maintain the stable state of mixed-polarized macrophages. Finally, we found that mixed-polarized macrophages were frequently detected in DGC tissues. CONCLUSION: These findings demonstrated that mixed-polarized macrophages exist as a novel subtype through the reciprocal interaction between DGC cells and nonmalignant cells.

A novel tdTomato transgenic mouse model to visualize FAP-positive cancer-associated fibroblasts.

Fibroblast activation protein (FAP) generally shows low or undetectable expression in most normal tissues but is highly expressed in fibroblasts in almost all carcinomas. FAP is one of the potential molecules to detect activated fibroblasts and has multiple roles in tumour progression. We generated transgenic mice that specifically expressed tdTomato along with FAP promoter activity. Coculturing a mouse gastric cancer cell line and FAP-tdTomato transgenic mouse-derived fibroblasts showed that tdTomato expression was elevated in the cocultured fibroblasts. Moreover, stomach wall transplanted tumours in mice also showed FAP-tdTomato expression in fibroblasts of the stomach and each metastatic legion. These results indicated that FAP-tdTomato expression in fibroblasts was elevated by stimulation through the interaction with cancer cells. Functionally, collagen production was increased in FAP/tdTomato-positive fibroblasts cocultured with mouse cancer cells. These FAP-tdTomato transgenic mice have the potential to be used to investigate real-time FAP dynamics and the importance of FAP expression in tumour development.

Cellular senescence in the tumor microenvironment and context-specific cancer treatment strategies.

Cellular senescence in cancer development is known to have tumor-suppressive and tumor-promoting roles. Recent studies have revealed numerous molecular mechanisms of senescence followed by senescence-associated secretory phenotype induction and showed the significance of senescence on both sides. Cellular senescence in stromal cells is one of the reasons for therapeutic resistance in advanced cancer; thus, it is an inevitable phenomenon to address while seeking an effective cancer treatment strategy. This review summarizes the molecular mechanisms regarding cellular senescence, focusing on the dual roles played by senescence, and offers some direction toward successful treatments targeting harmful senescent cells.

Tumor microenvironmental 15-PGDH depletion promotes fibrotic tumor formation and angiogenesis in pancreatic cancer.

The arachidonic acid cascade is a major inflammatory pathway that produces prostaglandin E2 (PGE2). Although inhibition of 15-hydroxyprostaglandin dehydrogenase (15-PGDH) is reported to lead to PGE2 accumulation, the role of 15-PGDH expression in the tumor microenvironment remains unclear. We utilized Panc02 murine pancreatic cancer cells for orthotopic transplantation into wild-type and 15-pgdh+/- mice and found that 15-pgdh depletion in the tumor microenvironment leads to enhanced tumorigenesis accompanied by an increase in cancer-associated fibroblasts (CAFs) and the promotion of fibrosis. The fibrotic tumor microenvironment is widely considered to be hypovascular; however, we found that the angiogenesis level is maintained in 15-pgdh+/- mice, and these changes were also observed in a genetically engineered PDAC mouse model. Further confirmation revealed that fibroblast growth factor 1 (FGF1) is secreted by pancreatic cancer cells after PGE2 stimulation, consequently promoting CAF proliferation and vascular endothelial growth factor A (VEGFA) expression in the tumor microenvironment. Finally, in 15-pgdh+/- Acta2-TK mice, depletion of fibroblasts inhibited angiogenesis and cancer cell viability in orthotopically transplanted tumors. These findings highlighted the role of 15-pgdh downregulation in enhancing PGE2 accumulation in the pancreatic tumor microenvironment and in subsequently maintaining the angiogenesis level in fibrotic tumors along with CAF expansion.

Intracellular MUC20 variant 2 maintains mitochondrial calcium homeostasis and enhances drug resistance in gastric cancer.

BACKGROUND: Signet ring cell carcinoma (SRCC) is a particular histologic variant of gastric cancer (GC). However, the critical factor related to the aggressive characteristics of SRCC has not been determined. METHODS: We collected surgically resected tissues from 360 GC patients in the Kumamoto University cohort and generated survival curves via the Kaplan-Meier method. In vitro, we identified the specific transcript variant of MUC20 in SRCC cells by direct sequencing and investigated the role of MUC20 in GC progression using GC cells with MUC20 silencing and forced expression. In vivo, we examined chemoresistance using MUC20 variant 2 (MUC20v2)-overexpressing non-SRCC cells to construct a xenograft mouse model. RESULTS: We analyzed a comprehensive GC cell line database to identify the specifically expressed genes in gastric SRCC. We focused on MUC20 and investigated its role in GC progression. Survival analysis revealed that GC patients with high MUC20 expression exhibited a poor prognosis and that MUC20 expression was significantly correlated with SRCC histological type. Moreover, we found that gastric SRCC cells specifically expressed MUC20v2, which was dominantly expressed in the cytoplasm. Silencing MUC20v2 caused cell death with characteristic morphological changes in gastric SRCC cells. To further determine the types of cell death, we examined apoptosis, pyroptosis and ferroptosis by detecting cleaved PARP, gasdermin E-N-terminal (GSDME-N), and lipid reactive oxygen species (ROS) levels, respectively. We found that apoptosis and pyroptosis occurred in MUC20-silenced gastric SRCC cells. In addition, MUC20v2-overexpressing GC cells exhibited chemoresistance to cisplatin (CDDP) and paclitaxel (PTX). RNA sequencing revealed that the pathways involved in intracellular calcium regulation were significantly upregulated in MUC20v2-overexpressing GC cells. Notably, forced expression of MUC20v2 in the cytoplasm of GC cells led to the maintenance of mitochondrial calcium homeostasis and mitochondrial membrane potential (MMP), which promoted cell survival and chemoresistance by suppressing apoptosis and pyroptosis. Finally, we investigated the significance of MUC20v2 in a xenograft model treated with CDDP and showed that MUC20v2 overexpression caused chemoresistance by inhibiting cell death. CONCLUSION: These findings highlight the novel functions of MUC20v2, which may confer cell survival and drug resistance in GC cells. SIGNIFICANCE: MUC20v2 protects GC cells from apoptosis and pyroptosis by maintaining mitochondrial calcium levels and mitochondrial membrane potential and subsequently induces drug resistance.

Single-Cell Atlas of Lineage States, Tumor Microenvironment, and Subtype-Specific Expression Programs in Gastric Cancer.

Gastric cancer heterogeneity represents a barrier to disease management. We generated a comprehensive single-cell atlas of gastric cancer (>200,000 cells) comprising 48 samples from 31 patients across clinical stages and histologic subtypes. We identified 34 distinct cell-lineage states including novel rare cell populations. Many lineage states exhibited distinct cancer-associated expression profiles, individually contributing to a combined tumor-wide molecular collage. We observed increased plasma cell proportions in diffuse-type tumors associated with epithelial-resident KLF2 and stage-wise accrual of cancer-associated fibroblast subpopulations marked by high INHBA and FAP coexpression. Single-cell comparisons between patient-derived organoids (PDO) and primary tumors highlighted inter- and intralineage similarities and differences, demarcating molecular boundaries of PDOs as experimental models. We complemented these findings by spatial transcriptomics, orthogonal validation in independent bulk RNA-sequencing cohorts, and functional demonstration using in vitro and in vivo models. Our results provide a high-resolution molecular resource of intra- and interpatient lineage states across distinct gastric cancer subtypes. SIGNIFICANCE: We profiled gastric malignancies at single-cell resolution and identified increased plasma cell proportions as a novel feature of diffuse-type tumors. We also uncovered distinct cancer-associated fibroblast subtypes with INHBA-FAP-high cell populations as predictors of poor clinical prognosis. Our findings highlight potential origins of deregulated cell states in the gastric tumor ecosystem. This article is highlighted in the In This Issue feature, p. 587.

Metabolic shift to serine biosynthesis through 3-PG accumulation and PHGDH induction promotes tumor growth in pancreatic cancer.

Cancer cells craftily adapt their energy metabolism to their microenvironment. Nutrient deprivation due to hypovascularity and fibrosis is a major characteristic of pancreatic ductal adenocarcinoma (PDAC); thus, PDAC cells must produce energy intrinsically. However, the enhancement of energy production via activating Kras mutations is insufficient to explain the metabolic rewiring of PDAC cells. Here, we investigated the molecular mechanism underlying the metabolic shift in PDAC cells under serine starvation. Amino acid analysis revealed that the concentrations of all essential amino acids and most nonessential amino acids were decreased in the blood of PDAC patients. In addition, the plasma serine concentration was significantly higher in PDAC patients with PHGDH-high tumors than in those with PHGDH-low tumors. Although the growth and tumorigenesis of PK-59 cells with PHGDH promoter hypermethylation were significantly decreased by serine starvation, these activities were maintained in PDAC cell lines with PHGDH promoter hypomethylation by serine biosynthesis through PHGDH induction. In fact, DNA methylation analysis by pyrosequencing revealed that the methylation status of the PHGDH promoter was inversely correlated with the PHGDH expression level in human PDAC tissues. In addition to PHGDH induction by serine starvation, PDAC cells showed enhanced serine biosynthesis under serine starvation through 3-PG accumulation via PGAM1 knockdown, resulting in enhanced PDAC cell growth and tumor growth. However, PHGDH knockdown efficiently suppressed PDAC cell growth and tumor growth under serine starvation. These findings provide evidence that targeting the serine biosynthesis pathway by inhibiting PHGDH is a potent therapeutic approach to eliminate PDAC cells in nutrient-deprived microenvironments.

Protocol to establish cancer-associated fibroblasts from surgically resected tissues and generate senescent fibroblasts.

Accumulating evidence suggests that the malignant behavior of cancer is influenced by stromal activity in the tumor microenvironment. Cancer-associated fibroblasts (CAFs), which are the main component of the cancerous stroma, play an important role in cancer development. Here, we describe a protocol to establish CAFs from surgically resected tissues. CAFs could be a vital tool for understanding the microenvironment and its impact on tumor progression and metastasis. Moreover, we generated inflammation-induced senescent fibroblasts that more closely mimic the tumor microenvironment. For complete details on the use and execution of this protocol, please refer to Yasuda et al. (2021).

Inflammation-driven senescence-associated secretory phenotype in cancer-associated fibroblasts enhances peritoneal dissemination.

In the tumor microenvironment, senescent non-malignant cells, including cancer-associated fibroblasts (CAFs), exhibit a secretory profile under stress conditions; this senescence-associated secretory phenotype (SASP) leads to cancer progression and chemoresistance. However, the role of senescent CAFs in metastatic lesions and the molecular mechanism of inflammation-related SASP induction are not well understood. We show that pro-inflammatory cytokine-driven EZH2 downregulation maintains the SASP by demethylating H3K27me3 marks in CAFs and enhances peritoneal tumor formation of gastric cancer (GC) through JAK/STAT3 signaling in a mouse model. A JAK/STAT3 inhibitor blocks the increase in GC cell viability induced by senescent CAFs and peritoneal tumor formation. Single-cell mass cytometry revealed that fibroblasts exist in the ascites of GC patients with peritoneal dissemination, and the fibroblast population shows p16 expression and SASP factors at high levels. These findings provide insights into the inflammation-related SASP maintenance by histone modification and the role of senescent CAFs in GC peritoneal dissemination.

Conflicting metabolic alterations in cancer stem cells and regulation by the stromal niche.

Recent studies have revealed that cancer stem cells (CSCs) undergo metabolic alterations that differentiate them from non-CSCs. Inhibition of specific metabolic pathways in CSCs has been conducted to eliminate the CSC population in many types of cancer. However, there is conflicting evidence about whether CSCs depend on glycolysis or mitochondrial oxidative phosphorylation (OXPHOS) to maintain their stem cell properties. This review summarizes the latest knowledge regarding CSC-specific metabolic alterations and offers recent evidence that the surrounding microenvironments may play an important role in the maintenance of CSC properties.

Functional diversity of cancer-associated fibroblasts in modulating drug resistance.

The effectiveness of current chemotherapies for cancer is gradually progressing; however achieving a complete cure through chemotherapy is still difficult and has been the main goal in treatment of advanced cancer. Drug resistance is an issue in cancer therapy, therefore increasing numbers of investigations into drug resistance have focused on the characteristics of the cancer cells themselves. The interaction between the tumor microenvironment (TME) and cancer cells is also intimately involved in the development of drug resistance. Cancer-associated fibroblasts (CAFs) are a predominant component of the TME and affect tumor progression by secreting soluble factors. This review summarizes the most up-to-date knowledge of CAFs and drug resistance in cancer, with a focus on factors secreted from CAFs including proteins, cytokines, extracellular vesicles, and metabolites. A perspective on the potential role of anti-CAF therapies in overcoming CAF-induced drug resistance is also discussed.

Extracellular Vesicles from Cancer-Associated Fibroblasts Containing Annexin A6 Induces FAK-YAP Activation by Stabilizing ß1 Integrin, Enhancing Drug Resistance.

Extracellular vesicles (EV) from cancer-associated fibroblasts (CAF) are composed of diverse payloads. Although CAFs impact the aggressive characteristics of gastric cancer cells, the contribution of CAF-EV to gastric cancer progression has not been elucidated. Here, we investigated the molecular mechanism of the changes in gastric cancer characteristics induced by CAF-EV. CAF abundance in gastric cancer tissues was associated with poor prognosis of patients with gastric cancer receiving chemotherapy. Moreover, CAF-EV induced tubular network formation and drug resistance of gastric cancer cells in the extracellular matrix (ECM). Comprehensive proteomic analysis of CAF-EV identified that Annexin A6 plays a pivotal role in network formation and drug resistance of gastric cancer cells in the ECM via activation of ß1 integrin-focal adhesion kinase (FAK)-YAP. A peritoneal metastasis mouse model revealed that CAF-EV induced drug resistance in peritoneal tumors, and inhibition of FAK or YAP efficiently attenuated gastric cancer drug resistance in vitro and in vivo. These findings demonstrate that drug resistance is conferred by Annexin A6 in CAF-EV and provide a potential avenue for overcoming gastric cancer drug resistance through the inhibition of FAK-YAP signaling in combination with conventional chemotherapeutics. SIGNIFICANCE: This study elucidates a novel molecular mechanism through which Annexin A6 in CAF-EV activates FAK-YAP by stabilizing ß1 integrin at the cell surface of gastric cancer cells and subsequently induces drug resistance. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/16/3222/F1.large.jpg.

A case of primary hepatic mucosa-associated lymphoid tissue lymphoma incidentally found in the sustained virological response state of chronic hepatitis C: review of the literature of this rare disease.

A 54-year-old woman finished the treatment for chronic hepatitis C and achieved sustained virological response. She was identified with some tumor lesions at her liver during follow-up observation by ultrasonography. From contrast-enhanced computed tomography, there were four tumors at sub-segment 4/5, S5, S6, and S7. These lesions are slightly enhanced on arterial phase and washed out on delayed phase. Contrast-enhanced magnetic resonance imaging showed slight enhancement on arterial phase and defect on hepatocyte phase. Tumor markers including alpha fetoprotein, Des-Gamma-Carboxy Prothrombin, carcinoembryonic antigen, and carbohydrate antigen (CA19-9) were within normal range. The patient underwent partial hepatectomies of four tumors at S4/5, S5, S6, and S7. The patient was recovering well, so he discharged our hospital after 10 days from the operation. The histological assay of the resected specimen showed accumulation of lymphocyte with hyperplasia of lymphoid follicles accordant with tumor lesions. Immunohistochemical staining assay revealed a positive for CD3, CD20, CD10, and bcl-2. These findings eventually made a diagnosis of all four tumors as mucosa-associated lymphoid tissue lymphoma. Since previously published case reports and our case described nonspecific clinical features of this rare disease, it was difficult to get the certain diagnosis before histological confirmation and non-anatomical partial liver resection may be a good choice for both diagnosis and local therapy.

Multiple heterochronic gastrointestinal stromal tumors in the stomach detected 6 years after resection: a case report.

BACKGROUND: To date, only a few cases of multiple GISTs with different clones in different organs have been published. However, a case of multiple GISTs with different clones occurring in a single organ has never been reported. CASE PRESENTATION: A 41-year-old patient underwent laparoscopic partial gastrectomy for gastric gastrointestinal stromal tumor (GIST) in 2012. The pathological findings showed high-risk characteristics for recurrence, so he received adjuvant therapy with imatinib for 3 years. In 2018, 3 years after completing the adjuvant therapy, tumor lesions at residual gastric cardia were incidentally identified by follow-up computed tomography (CT). The pathological findings of the tumor biopsy revealed gastric GIST. He underwent secondary laparoscopic partial gastrectomy and was diagnosed with high-risk GIST. Adjuvant therapy with imatinib was restarted immediately. The two gastric GISTs had the same exon 11 mutations in the c-kit gene, but they had different missense mutations. This molecular heterogeneity suggested that they were derived from different origins. CONCLUSION: We reported a multiple heterochronic GIST in the stomach detected 6 years after resection. There may be a possibility that another heterochronic GIST will occur in the remnant stomach in the future, so close follow-up will be needed.