The role of cytoreductive surgery and HIPEC for the treatment of primary and secondary peritoneal malignancies-experience from a tertiary care center in Germany.

PURPOSE: Peritoneal surface malignancies (PSM) are commonly known to have a dismal prognosis. Over the past decades, novel techniques such as cytoreductive surgery (CRS), hyperthermic intraperitoneal chemotherapy (HIPEC), and pressurized intraperitoneal aerosol chemotherapy (PIPAC) have been introduced for the treatment of PSM which could improve the overall survival and quality of life of patients with PSM. The decision to proceed with CRS and HIPEC is often challenging due the complexity of the disease, the extent of the procedure, associated side effects, and potential risks. Here, we present our experience with CRS and HIPEC to add to the ongoing discussion about eligibility criteria, technical approach, and expected outcomes and contribute to the evolution of this powerful and promising tool in the multidisciplinary treatment of patients with primary and secondary PSM. METHODS: A single-center retrospective chart review was conducted and included a total of 40 patients treated with CRS and HIPEC from April 2020 to September 2022 at the University Hospital Münster Department of Surgery. All patients had histologically confirmed primary or secondary peritoneal malignancies of various primary origins. RESULTS: Our study included 22 patients with peritoneal metastases from gastric cancer (55%), 8 with pseudomyxoma peritonei (20%), 4 with mesothelioma of the peritoneum (10%), and 6 patients with PSM originating from other primary tumor locations. Median PCI at time of cytoreduction was 4 (0-25). Completeness of cytoreduction score was 0 in 37 patients (92.5%), 1 in two patients (5%), and 2 in one patient (2.5%). Median overall survival across all patients was 3.69 years. CONCLUSION: Complete cytoreduction during CRS and HIPEC can be achieved for patients with low PCI, for patients with high PCI in low-grade malignancies, and even for patients with initially high PCI in high-grade malignancies following a significant reduction of cancer burden due to extensive preoperative treatment with PIPAC and systemic chemotherapy.

Neoadjuvant chemotherapy does not improve survival for patients with high volume colorectal peritoneal metastases undergoing cytoreductive surgery.

BACKGROUND: Colorectal peritoneal metastases (CRPM) affects 15% of patients at initial colorectal cancer diagnosis. Neoadjuvant chemotherapy (NAC) prior to cytoreductive surgery (CRS) has been demonstrated to be a safe and feasible option, however there is limited data describing its efficacy in advanced peritoneal disease. This study evaluated the effect of NAC on survival in patients with high volume CRPM undergoing CRS with or without HIPEC. METHODS: A retrospective review of all patients who underwent CRS with or without HIPEC for CRPM from 2004 to 2019 at our institution was performed. The cohort was divided based on peritoneal carcinomatosis index (PCI) at surgery: Low Volume (PCI ≤ 16) and High Volume (PCI > 16). RESULTS: A total of 326 patients underwent CRS with HIPEC for CRPM. There were 39 patients (12%) with High Volume disease, and 15 of these (38%) received NAC. Patients with High Volume disease had significantly longer operating time, lower likelihood of complete macroscopic cytoreduction (CC-0 score), longer intensive care unit length of stay and longer hospital stay compared to Low Volume disease. In High Volume disease, the NAC group had a significantly shorter median survival of 14.4 months compared to 23.8 months in the non-NAC group (p = 0.046). CONCLUSION: Patients with High Volume CRPM achieved good median survival following CRS with HIPEC, which challenges the current PCI threshold for offering CRS. The use of NAC in this cohort did not increase perioperative morbidity but was associated with significantly shorter median survival compared to upfront surgery.

Complexity of surgery and treatment burden in patients with peritoneal malignancy is not determined by addition of hyperthermic intraperitoneal chemotherapy.

BACKGROUND: This study describes surgical and quality of life outcomes in patients with peritoneal malignancy treated by cytoreductive surgery (CRS) alone compared with a subgroup treated with CRS and hyperthermic intraperitoneal chemotherapy (HIPEC). METHODS: Peritoneal malignancy patients undergoing surgery between 2017 and 2023 were included. The cohort was divided into patients treated by CRS and HIPEC and those treated by CRS without HIPEC (including CRS only or maximal tumour debulking (MTB)). Main outcomes included surgical outcomes, survival, and quality of life. Groups were compared using non-parametric tests and log-rank test was used to compare survival curves. RESULTS: 403 had CRS and HIPEC, 25 CRS only and 15 MTB. CRS and HIPEC patients had a lower peritoneal carcinomatosis index (12.0 vs. 17.0 vs. 35.0; P < 0.001) and longer surgical operative time (9.3 vs. 8.3 vs. 5.2 h; P < 0.001), when compared to CRS only and MTB, respectively. No other significant difference between groups was observed. CONCLUSIONS: The optimal management of selected patients with resectable peritoneal malignancy incorporates a combined strategy of CRS and HIPEC. When HIPEC is not utilized, due to significant residual disease or comorbidity precluding safe delivery, CRS alone is associated with good outcomes. Hospital stay and complications are acceptable but not significantly different to the CRS and HIPEC group. CRS alone is a complex intervention requiring comparable resources with good outcomes. In view of our findings 'intention to treat' with CRS and HIPEC should be the basis for resource allocation and funding.

Peritoneal carcinomatosis in mouse models.

Peritoneal carcinomatosis (PCa) represents a metastatic stage of a disease with unmet therapeutic options. Malignant cells from primary tumors (gastrointestinal or gynecologic malignancies) invade the peritoneal cavity and eventually seed onto peritoneal surfaces, with the omentum being the most common nest area. With a median survival of less than 6 months, PCa has a dismal prognosis that can be improved with treatments only available to a select few individuals with low tumor burden. Thus, the discovery of novel and effective therapies for this disease depends on reliable animal models. Here, we describe a method to generate syngeneic PCa mouse models based on intraperitoneal (i.p.) administration of tumor cells. This model allows to follow-up cancer progression in PCa models from ovarian and colorectal origins monitoring mice bodyweight changes, ascites development and overall survival. Moreover, luciferase-expressing tumor cells can also be used to assess tumor growth after i.p. injection through in vivo bioluminescence quantification. The establishment of reliable, easy-to-monitor and reproducible intraperitoneal syngeneic tumors models, as described here, is the first step to develop cutting-edge therapies against PCa.

Ruptured Ovarian Cystic Teratoma: A Rare Diagnosis, Easily to Be Confused with Peritoneal Carcinomatosis.

Although ovarian cystic teratoma is the most common ovarian tumor, complications are quite rare. However, it is important to be recognized by the radiologist in order to avoid inaccurately diagnosing them as malignant lesions. This case report describes a 61-year-old postmenopausal woman, who presented to the emergency room with abdominal pain following a minor blunt abdominal trauma. In this context, a CT scan was performed, which showed the presence of round, hypodense masses randomly distributed in the peritoneum, with coexisting ascites in moderate amount; ovarian carcinoma with peritoneal carcinomatosis was suspected. The patient was hospitalized and an MRI of the abdomen and pelvis was recommended for a more detailed lesion characterization. Following this examination, the patient was diagnosed with mature cystic ovarian teratoma complicated by rupture. Surgery was performed, and the outcome was favorable. The cases of ruptured cystic teratomas are rare, and to our knowledge, this is the first occurrence described in literature. Special attention must be paid when confronting with such a case in medical practice, since it can easily misdiagnosed as peritoneal carcinomatosis.

TGF-ß-driven LIF expression influences neutrophil extracellular traps (NETs) and contributes to peritoneal metastasis in gastric cancer.

Gastric cancer (GC), notorious for its poor prognosis, often advances to peritoneal dissemination, a crucial determinant of detrimental outcomes. This study intricately explores the role of the TGFß-Smad-LIF axis within the tumor microenvironment in propagating peritoneal metastasis, with a specific emphasis on its molecular mechanism in instigating Neutrophil Extracellular Traps (NETs) formation and encouraging GC cellular functions. Through a blend of bioinformatics analyses, utilizing TCGA and GEO databases, and meticulous in vivo and in vitro experiments, LIF was identified as pivotally associated with GC metastasis, notably, enhancing the NETs formation through neutrophil stimulation. Mechanistically, TGF-ß was substantiated to elevate LIF expression via the activation of the Smad2/3 complex, culminating in NETs formation and consequently, propelling peritoneal metastasis of GC. This revelation uncovers a novel potential therapeutic target, promising a new avenue in managing GC and mitigating its metastatic propensities.

Safety and efficacy of sirolimus in recurrent intravenous leiomyomatosis, pulmonary benign metastatic leiomyomatosis, and leiomyomatosis peritonealis disseminata: a pilot study.

BACKGROUND: Intravenous leiomyomatosis (IVL), pulmonary benign metastatic leiomyomatosis (PBML), and leiomyomatosis peritonealis disseminata (LPD) are leiomyomas with special growth patterns and high postoperative recurrence rates. We report the safety and efficacy of a pilot study of sirolimus in the treatment of recurrent IVL, PBML, and recurrent LPD. METHODS: This was a pilot study to evaluate the safety and efficacy of sirolimus in the treatment of leiomyomatosis (ClinicalTrials.gov identifier NCT03500367) conducted in China. Patients received oral sirolimus 2 mg once a day for a maximum of 60 months or until disease progression, intolerable toxicity, withdrawal of consent, or investigator decision to stop. The primary end point of this study was the objective response rate. Secondary end points included safety and tolerability, disease control rate, and progression-free survival. RESULTS: A total of 15 patients with leiomyomatosis were included in the study, including five with recurrent IVL, eight with PBML and two with recurrent LPD. The median follow-up time was 15 months (range 6-54 months), nine patients (60%) had treatment-related adverse events (including all levels), and two patients had treatment-related grade 3 or 4 adverse events. The objective response rate was 20.0% (95% CI, 7.1-45.2%), and the disease control rate was 86.7% (95% CI, 62.1-96.3%). Partial response was achieved in three patients. The median response time in the three partial response patients was 33 months (range 29-36 months), and the sustained remission time of these three patients reached 0, 18, and 25 months, respectively. CONCLUSIONS: Sirolimus was safe and effective in the treatment of recurrent IVL, PBML, and recurrent LPD. TRIAL REGISTRATION: ClinicalTrials.gov identifier NCT03500367. Registered on 18 April 2018.

Doxorubicin as Risk Factor for Fascial Dehiscence After CRS-HIPEC for Peritoneal Metastases.

BACKGROUND/AIM: Among postoperative complications, fascial dehiscence (FD) is registered in up to 10% of patients after cytoreductive surgery and hyperthermic intraperitoneal chemotherapy (CRS-HIPEC). This study aimed to evaluate the risk factors related to FD after CRS-HIPEC. PATIENTS AND METHODS: A retrospective analysis of a prospectively maintained database of consecutive patients who underwent CRS-HIPEC between 2015 and 2023 was performed. For each patient, risk factors for postoperative fascial dehiscence were identified using multivariate analysis. RESULTS: During the study period (2018-2023), 217 patients were treated with CRS-HIPEC. The incidence of FD was observed in seven cases (3.2%), which were reoperated with direct fascial closure. In three cases, FD was associated with other grade III-IV complications. Body mass index, (BMI; p=0.024), doxorubicin-based HIPEC (p=0.005), and open technique (p=0.004) were identified as risk factors for FD in univariate analysis. Systemic chemotherapy, prior surgical score, and peritoneal cancer index (PCI) were not associated with an increased risk of FD. In multivariable regression analysis, doxorubicin-based HIPEC and open technique were confirmed as risk factors for FD. CONCLUSION: Although FD is a relatively rare event after CRS-HIPEC, open technique and doxorubicin-based HIPEC were significant predictors of this complication. Specific fascial closure techniques and proper wound care should be considered in high-risk patients.

Real-world study of lymphadenectomy in patients with advanced epithelial ovarian cancer.

BACKGROUND: The evidence on the role of retroperitoneal lymphadenectomy is limited to less common histology subtypes of epithelial advanced ovarian cancer. METHODS: This retrospective cohort study utilized data from the Surveillance, Epidemiology, and End Results Program from January 1, 2010, to December 31, 2019. Patients with stage III-IV epithelial ovarian cancer were included and divided into two groups based on whether they received retroperitoneal lymphadenectomy. The primary outcomes are overall survival (OS) and cause-specific survival (CSS). RESULTS: Among the 10 184 included patients, 5472 patients underwent debulking surgery with retroperitoneal lymphadenectomy, while 4712 patients only underwent debulking surgery. No differences were found in the baseline information between the two groups after propensity score matching. Retroperitoneal lymphadenectomy during debulking surgery was associated with improved 5-year OS (43.41% vs. 37.49%, p < 0.001) and 5-year CSS (46.43% vs. 41.79%, p < 0.001). Subgroup analysis further validate the retroperitoneal lymphadenectomy increased the 5-year OS and CSS in patients with high-grade serous cancer. Although the results were not validated in the less common ovarian cancer (including endometrial cancer, mucinous cancer, low-grade serous cancer, and clear cell cancer), the tendency showed patients with the above four subtypes may benefit from the lymphadenectomy which is restricted for small sample size after propensity score matching. CONCLUSIONS: This study revealed that retroperitoneal lymphadenectomy could further improve the survival outcome during debulking surgery in patients with advanced epithelial ovarian cancer. The conclusion was affected by the histology subtypes of ovarian cancer and further studies are needed to validate the conclusion in less common ovarian cancer.

Outcomes following cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC) for peritoneal malignancies: 10 ​Year experience.

INTRODUCTION: The treatment of peritoneal malignancies has evolved and select patients can undergo effective surgical therapies. Access to innovative oncology procedures can be improved if programs are developed within and outside of academic cancer centers. We report the creation of a high volume, comprehensive peritoneal malignancy program developed in a community center. METHODS: A retrospective single-site study was conducted using registry data comprising all patients who underwent Cytoreductive Surgery (CRS) and Heated Intraperitoneal Chemotherapy (HIPEC) between October 2011-December 2021. RESULTS: 353 patients underwent CRS and HIPEC. 208 patients experienced in-hospital morbidity (58.9 â€‹%). Group comparison by disease site, PCI, and the completeness of cytoreduction demonstrated survival differences in mean overall survival and disease-free survival in 1-, 3- and 5-year ranges. CONCLUSIONS: This study demonstrates that with a standardized protocol and a surgeon-led multidisciplinary team it is possible to offer safe outcome driven, complex oncologic surgery in a community-based cancer program.

Building an Efficient Peritoneal Surface Malignancies Program Despite the Lower-Middle-Income Barriers: Ukraine Experience.

PURPOSE: Cytoreductive surgery/hyperthermic intraperitoneal chemotherapy (CRS/HIPEC) programs are often limited to centers in developed countries because of extensive requirements. We aimed to analyze efficacy and challenges of CRS/HIPEC centers in lower-middle-income settings in the Ukraine example. METHODS: A multicenter descriptive study was conducted using data sets (2008-2022) from Kyiv, Lviv, and Odesa centers. Patients with appendiceal neoplasm (AN); colorectal cancer (CRC); malignant peritoneal mesothelioma (MPM); and epithelial ovarian, fallopian tube, and primary peritoneal cancer (EOC) treated with CRS ± HIPEC were included. Overall survival (OS) was analyzed for N ≥ 20 cohorts using the Kaplan-Meier method. RESULTS: We included 596 patients. At Kyiv and Lviv centers, 37 and 28 patients with AN had completeness of cytoreduction (CC-0/1) rates of 84% and 71%, respectively. Thirty-day major morbidity stood at 24% and 18%, respectively. Median OS was not reached (NR) at both centers. Nineteen patients with CRC from Kyiv, 11 from Lviv, and 156 from Odesa had CC-0/1 rates of 84%, 91%, and 86%, respectively. Thirty-day major complications occurred in 16%, 18%, and 8%, respectively. Median OS in the Odesa cohort was 35 (95% CI, 32 to 38) months. Among 15 Kyiv, five Lviv, and six Odesa patients with MPM, CC-0/1 rates were 67%, 80%, and 100%, respectively, while major complications occurred in 13%, 0%, and 17%, respectively. OS was not analyzed because of small MPM cohorts. At Kyiv, Lviv, and Odesa centers, 91, 40, and 89 patients, respectively, had primary EOC. CC-0/1 rates were 79%, 100%, and 80%, and 30-day major morbidity rates were 23%, 5%, and 6%, respectively. Median OS was NR, 71 (95% CI, 32 to 110), and 67 (95% CI, 61 to 73) months, respectively. CONCLUSION: CRS/HIPEC programs in lower-middle-income environment can achieve safety and survival that meet global standards. Our discussion highlights common obstacles in such settings and proposes effective overcoming strategies.

Feasibility of Robot-Assisted Cytoreductive Surgery With Upper-Abdominal Peritonectomy for Pseudomyxoma Peritonei With Low Peritoneal Carcinomatosis Index: A Pilot Study.

INTRODUCTION: Our study's objective was to provide the method for, and preliminary findings from, robot-assisted cytoreductive surgery (r-CRS) combined with upper-abdominal peritonectomy in pseudomyxoma peritonei (PMP) with limited peritoneal surface malignancy (PSM). MATERIALS AND METHODS: We conducted a retrospective pilot study on consecutive patients with PSM secondary to pseudomyxoma peritonei with a peritoneal cancer index (PCI) of under 10 who were indicated for r-CRS combined with upper-abdominal peritectomy. Perioperative and 30-day major morbidity and mortality characteristics were analyzed and compared with cases in which laparoscopic CRS (l-CRS) was performed under the same conditions. RESULTS: Six patients underwent r-CRS combined with an upper-abdominal partial peritonectomy. Their mean PCI was 4.83. Complete cytoreduction was achieved in all patients. The mean duration of the operation was 156.8 minutes. There was no major complication and no mortality. The mean length of hospital stay after surgery was 6.33 days. r-CRS resulted in less blood loss, a lower C-reactive protein level, and a shorter length of hospital stay that were significantly different compared with those of l-CRS. CONCLUSIONS: This is the initial technical report of a robotic approach for CRS combined with upper-abdominal peritonectomy. r-CRS with a combined upper-abdominal peritonectomy was shown to be safe and feasible for PMP with limited PSM.

Intense FDG Uptake in Leiomyomatosis Peritonealis Disseminata With Fumarate Hydratase Deficiency.

ABSTRACT: A 35-year-old woman with a history of laparoscopic myomectomy presented with repeated abdominal pain. Contrast-enhanced abdominal and pelvic CT showed multiple enhancing solid or mixed cystic and solid peritoneal masses, and an enhancing uterine mass. All these masses showed intense FDG uptake on FDG PET/CT. The intraperitoneal and uterine masses were surgically removed. The histological and immunohistochemical findings of the peritoneal lesions were consistent with leiomyomatosis peritonealis disseminata with fumarate hydratase deficiency, and the uterine mass was adenomyosis. This case indicates fumarate hydratase-deficient extrauterine leiomyoma can show intense FDG uptake mimicking malignancy.

Cytoreductive surgery and hyperthermic intraperitoneal chemotherapy in New Zealand: peri-operative outcomes and service development over a decade.

BACKGROUND: Cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC) is the standard of care for selected cases of peritoneal surface malignancy. However, due to its morbidity and learning curve, it is only delivered in six centres in Australia and Aotearoa New Zealand (AoNZ). In this study, we report peri-operative morbidity and mortality following CRS/HIPEC at Waikato and Braemar Hospitals, which have treated patients from all regions of AoNZ since 2008. METHODS: We retrospectively reviewed a database of all patients undergoing CRS and HIPEC from 01/01/2008 to 01/11/2020 at Waikato and Braemar Hospitals. RESULTS: Two-hundred and forty procedures were performed for 221 patients with a mean age of 55, including 22 (9.2%) re-do procedures. One hundred and eighty-six cases were European, 32 were Maori, and 16 were Pasifika. There were 152 pseudomyxoma peritonei, 39 colorectal adenocarcinomas, 29 appendiceal cancers, 8 ovarian cancers, 6 peritoneal mesothelioma, and 6 other tumour types. The median PCI was 16. HIPEC was administered to 196 out of 196 CC0/1 cases (100%) and 3 out of 44 CC2/3 cases (6.8%). Fifty-six cases (23.3%) had at least one major complication. There were two mortalities (0.8%) within 30 days. The median length of stay was 11 days. Operative duration was identified as an independent risk factor for major complications. There was considerable variation in the number of referrals from different regions of AoNZ. Over time, a decline in major complication rate is seen with increased case volume. CONCLUSION: The Waikato region has achieved favourable short-term outcomes following CRS/HIPEC.

High-grade B-cell lymphoma, not otherwise specified, presenting as primary peritoneal lymphomatosis and successfully treated with dose-adjusted EPOCH-R.

Peritoneal lymphomatosis (PL) is a rare lymphoma-associated condition defined as the dissemination of lymphoma cells in the peritoneum. An 82-year-old man presented with abdominal pain, heartburn, and high fever. Radiological findings, including positron emission tomography-computed tomography (PET-CT), and gastrointestinal fiberscopy, showed diffuse thickening of the peritoneum, omentum, and mesentery; however, no lymphadenopathy, hepatosplenomegaly, or gastrointestinal lesions were observed. Under suspicion of peritonitis carcinomatosa of unknown origin, exploratory laparoscopy was performed that revealed multiple white nodules and masses on the surfaces of the peritoneum, mesentery, and intestinal serosa. The histopathological and cytogenetic findings of the peritoneum revealed high-grade B-cell lymphoma, not otherwise specified, and a gain of MYC by fluorescence in-situ hybridization. The patient was treated with two cycles of R-CHOP therapy, followed by six cycles of dose-adjusted EPOCH-R therapy, and a complete metabolic response was confirmed by PET-CT. Since there are no specific radiological findings to confirm the diagnosis of PL, a histopathological diagnosis is usually required. Most PL exhibit an aggressive lymphoma phenotype and can be cured by appropriate chemotherapy. Therefore, early diagnosis and treatment are desirable.

Optimal peritoneal cancer index cutoff point for predicting surgical resectability of pseudomyxoma peritonei in treatment-naive patients.

BACKGROUND: The peritoneal cancer index (PCI) has been used to predict surgical outcomes for pseudomyxoma peritonei (PMP). The present study aimed to establish the optimal cutoff point for PCI to predict surgical resectability of PMP. METHODS: A total of 366 PMP patients were included. The patients were divided into low-grade and high-grade groups. Based on the completeness of the cytoreduction (CC) score, both low-grade and high-grade PMP patients were further divided into complete cytoreductive surgery (CRS) and maximal tumor debulking (MTD) subgroups. The ability to predict surgical resectability of total and selected PCI (regions 2 + 9 to 12) was analyzed through receiver operating characteristic (ROC) curves. RESULTS: Both total and selected PCI demonstrated excellent discriminative ability in predicting surgical resectability for low-grade PMP patients (n = 266), with the ROC-AUC of 0.940 (95% CI: 0.904-0.965) and 0.927 (95% CI: 0.889-0.955). The corresponding optimal cutoff point was 21 and 5, respectively. For high-grade PMP patients (n = 100), both total and selected PCI exhibited good performance in predicting surgical resectability, with the ROC-AUC of 0.894 (95% CI: 0.816-0.946) and 0.888 (95% CI: 0.810-0.943); correspondingly, the optimal cutoff point was 25 and 8, respectively. The discriminative ability between total and selected PCI in predicting surgical resectability did not show a statistical difference. CONCLUSIONS: Both total and selected PCI exhibited good performance and similarity in predicting complete surgical resection for both low-grade and high-grade PMP patients. However, the selected PCI was simpler and time-saving in clinical practice. In the future, new imaging techniques or predictive models may be developed to better predict PCI preoperatively, which might assist in confirming whether complete surgical resection can be achieved.

Malignant Peritoneal Mesothelioma Complicating Familial Mediterranean Fever on 18 F-FDG PET/CT.

ABSTRACT: A 77-year-old man with a personal history of familial Mediterranean fever presented with a slowly enlarging tumefaction of the left abdominal wall and persistent inflammatory syndrome despite good adherence to colchicine. 18 F-FDG PET/CT showed a hypermetabolic muscular mass of the abdominal wall along with other hypermetabolic lesions including a peritoneal mass and several subcutaneous soft tissue nodules. CT-guided needle biopsy led to the diagnosis of a muscular localization of a malignant peritoneal mesothelioma, which is an extremely rare complication of familial Mediterranean fever. Six courses of chemotherapy with carboplatin and pemetrexed allowed an almost complete response.

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.