Insufficient ability of omental milky spots to prevent peritoneal tumor outgrowth supports omentectomy in minimal residual disease

A randomized controlled trial to compare short-term outcomes following infragastric and infracolic omentectomy at the time of primary debulking surgery for epithelial ovarian cancer with normal-appearing omentum

BACKGROUND

Omentectomy is an important procedure in surgery for epithelial ovarian cancer, but the scope of omentectomy is not recommended in the guidelines. This study was performed to evaluate the benefits and risks of infragastric omentectomy in patients with epithelial ovarian cancer.

METHODS

This trial is a single center prospective study. Primary epithelial ovarian cancer patients with normal-appearing omentum were randomly assigned to either the control or experimental group and underwent infracolic or infragastric omentectomy, respectively. The primary endpoint was progression-free survival. This trial is registered on Chinese clinical trial registry site (ChiCTR1800018771).

RESULTS

A total of 106 patients meeting the inclusion criteria for ovarian cancer were included during the study period. Of these, 53 patients underwent infracolic omentectomy, whereas 53 patients received infragastric omentectomy. Multivariate analysis revealed that infragastric omentectomy could improve the detection rate of omental metastases (OR: 6.519, P = 0.005). Infragastric omentectomy improved progression-free survival significantly for those cases with higher than stage IIB disease (HR: 0.456, P = 0.041). Based on the short-term results, infragastric omentectomy did not cause more perioperative complications.

CONCLUSIONS

Compared with infracolic omentectomy, infragrastric omentectomy may be a more appropriate surgical procedure for stage IIB-IIIC epithelial ovarian cancer patients with normal-appearing omentum.

Exosomes secreted by ST3GAL5high cancer cells promote peritoneal dissemination by establishing a premetastatic microenvironment

Peritoneal dissemination of cancer affects patient survival. The behavior of peritoneal mesothelial cells (PMCs) and immune cells influences the establishment of a microenvironment that promotes cancer cell metastasis in the peritoneum. Here, we investigated the roles of lactosylceramide alpha-2,3-sialyltransferase (ST3G5; also known as ST3GAL5 and GM3 synthase) in the exosome-mediated premetastatic niche in peritoneal milky spots (MSs). Exosomes secreted from ST3G5high cancer cells (ST3G5high -cExos) were found to contain high levels of hypoxia-inducible factor 1-alpha (HIF1α) and accumulated in MSs via uptake in macrophages (MΦs) owing to increased expression of sialic acid-binding Ig-like lectin 1 (CD169; also known as SIGLEC1). ST3G5high -cExos induced pro-inflammatory cytokines and glucose metabolic changes in MΦs, and the interaction of these MΦs with PMCs promoted mesothelial-mesenchymal transition (MMT) in PMCs, thereby generating αSMA+ myofibroblasts. ST3G5high -cExos also increased the expression of immune checkpoint molecules and T-cell exhaustion in MSs, which accelerated metastasis to the omentum. These events were prevented following ST3G5 depletion in cancer cells. Mechanistically, ST3G5high -cExos upregulated chemokines, including CC-chemokine ligand 5 (CCL5), in recipient MΦs and dendritic cells (DCs), which induced MMT and immunosuppression via activation of signal transducer and activator of transcription 3 (STAT3). Maraviroc, a C-C chemokine receptor type 5 (CCR5) antagonist, prevented ST3G5high -cExo-mediated MMT, T-cell suppression, and metastasis in MSs. Our results suggest ST3G5 as a suitable therapeutic target for preventing cExo-mediated peritoneal dissemination.

Loss of B1 and marginal zone B cells during ovarian cancer

Recent advances in immunotherapy have not addressed the challenge presented by ovarian cancer. Although the peritoneum is an "accessible" locus for this disease there has been limited characterization of the immunobiology therein. We investigated the ID8-C57BL/6J ovarian cancer model and found marked depletion of B1 cells from the ascites of the peritoneal cavity. There was also selective loss of the B1 and marginal zone B cell subsets from the spleen. Immunity to antigens that activate these subsets validated their loss rather than relocation. A marked influx of myeloid-derived suppressor cells correlated with B cell subset depletion. These observations are discussed in the context of the housekeeping burden placed on innate B cells during ovarian cancer and to foster consideration of B cell biology in therapeutic strategies to address this challenge.

Specific Tumor Localization of Immunogenic Lipid-Coated Mesoporous Silica Nanoparticles following Intraperitoneal Administration in a Mouse Model of Serous Epithelial Ovarian Cancer

Immunogenic lipid-coated mesoporous silica nanoparticles (ILM) present pathogen-associated molecular patterns (PAMPs) on the nanoparticle surface to engage pathogen-associated receptors on immune cells. The mesoporous core is capable of loading additional immunogens, antigens or drugs. In this study, the impact of lipid composition, surface potential and intercalation of lipophilic monophosphoryl lipid A (MPL-A) in the lipid coat on nanoparticle properties and cellular interactions is presented. Loading and retention of the model antigen ovalbumin into the mesoporous silica core were found to be similar for all nanoparticle formulations, with presentation of ova peptide (SIINFEKL) by major histocompatibility complex (MHC) evaluated to facilitate the selection of an anionic nanoparticle composition. ILM were able to induce lysosomal tubulation and streaming of lysosomes towards the cell surface in dendritic cells, leading to an enhanced surface presentation of MHC. Myeloid cells robustly internalized all ILM formulations; however, non-myeloid cells selectively internalized cationic ILM in vitro in the presence of 20% serum. Interestingly, ILM administration to the peritoneal cavity of mice with disseminated ovarian cancer resulted in selective accumulation of ILM in tumor-associated tissues (>80%), regardless of nanoparticle surface charge or the presence of MPL-A. Immunofluorescence analysis of the omental tumor showed that ILMs, regardless of surface charge, were localized within clusters of CD11b+ myeloid cells 24 h post administration. Selective uptake of ILMs by myeloid cells in vivo indicates that these cells outcompete other cell populations in the ovarian tumor microenvironment, making them a strong target for therapeutic interventions.

A 3D multi-cellular tissue model of the human omentum to study the formation of ovarian cancer metastasis

Reliable and predictive experimental models are urgently needed to study metastatic mechanisms of ovarian cancer cells in the omentum. Although models for ovarian cancer cell adhesion and invasion were previously investigated, the lack of certain omental cell types, which influence the metastatic behavior of cancer cells, limits the application of these tissue models. Here, we describe a 3D multi-cellular human omentum tissue model, which considers the spatial arrangement of five omental cell types. Reproducible tissue models were fabricated combining permeable cell culture inserts and bioprinting technology to mimic metastatic processes of immortalized and patient-derived ovarian cancer cells. The implementation of an endothelial barrier further allowed studying the interaction between cancer and endothelial cells during hematogenous dissemination and the impact of chemotherapeutic drugs. This proof-of-concept study may serve as a platform for patient-specific investigations in personalized oncology in the future.

Development of the Peritoneal Metastasis: A Review of Back-Grounds, Mechanisms, Treatments and Prospects

Peritoneal metastasis is a malignant disease which originated from several gastrointestinal and gynecological carcinomas and has been leading to a suffering condition in patients for decades. Currently, as people have gradually become more aware of the severity of peritoneal carcinomatosis, new molecular mechanisms for targeting and new treatments have been proposed. However, due to the uncertainty of influencing factors involved and a lack of a standardized procedure for this treatment, as well as a need for more clinical data for specific evaluation, more research is needed, both for preventing and treating. We aim to summarize backgrounds, mechanisms and treatments in this area and conclude limitations or new aspects for treatments.

Assessment of prognostic and reproductive outcomes of omentectomy for patients with clinically apparent early-stage (I, II) malignant ovarian germ cell tumours: A multicentre retrospective study

OBJECTIVE

This study assessed the effect of omentectomy on the prognosis and fertility in patients with clinically early-stage (I, II) malignant ovarian germ cell tumours (MOGCT).

DESIGN

A retrospective multicentre study.

SETTING

Four university teaching hospitals in China.

POPULATION

A total of 268 patients with clinically apparent early-stage (I, II) MOGCT.

METHODS

Data were obtained from the medical records. Additionally, the propensity score matching (PSM) algorithm was adopted.

MAIN OUTCOME MEASURES

Prognostic outcomes were disease-free survival (DFS) and overall survival (OS). Fertility outcomes were pregnancy and live birth rates.

RESULTS

A total of 187 (69.8%) patients underwent omentectomy. Kaplan-Meier analysis showed no significant differences in DFS and OS between the omentectomy and non-omentectomy groups before and after PSM (p > 0.05). Additionally, subgroup analysis stratified by age (<18 and ≥18 years) showed similar results. International Federation of Gynecology and Obstetrics (FIGO) stage was the only risk factor associated with DFS (hazard ratio [HR] 14.71, 95% confidence interval [CI] 4.47-48.38, p < 0.001) and OS (HR 37.36, 95% CI 3.87-361.16, p = 0.002). Pregnancy and live birth rates in the total population were 80.3% and 66.7%, respectively. There were no significant differences between the two groups before and after PSM.

CONCLUSIONS

Omentectomy did not improve survival or affect fertility in patients with clinically apparent early-stage (I, II) MOGCT, regardless of the age. The clinical FIGO stage was an independent risk factor for recurrence and death.

Occult Omental Metastasis in Gastric Adenocarcinoma: An Analysis of Incidence, Predictors, and Outcomes

Negine PaulIntroduction  Traditionally, the concept of complete omentectomy during gastric resection for cancer was based on lymphatic drainage and the occurrence of occult omental metastasis (OM). However, recent emerging evidence has challenged this concept of complete omentectomy. We, therefore, aim to find the incidence and risk factors of occult OM and also evaluate the outcome of patients with and without such metastasis. Methods  This is a single institutional, retrospective study of patients with gastric cancer who underwent curative radical gastrectomy for a period of 3 years (April 1, 2016, to March 31, 2019). A complete omentectomy was performed in all patients and the omentum and nodal stations were dissected in the resected specimen and sent for pathological analysis. Clinical and epidemiological data were collected from the hospital patient database and analysis was done. Results  A total of 185 patients have been included in the study, with a mean age of 53.84 years. Twenty of the 185 patients had OM (10.8%). Age, sex, location of the tumor, and neoadjuvant chemotherapy were not statistically significant in predicting OM. However, tumor size and tumor depth were found to have a significant association with OM. The occurrence of OM was more likely to be associated with disease recurrence, especially in the peritoneum. The mean overall survival was 38.15 months (±3.33 SD), whereas patients with OM had lower survival, 23.31 months (±7.79 SD), with a p -value of 0.012. Conclusion  OM was not encountered in T1 and T2 gastric cancers and the incidence of OM in T3 and T4 tumors was approximately 12.7%. Therefore, complete omentectomy may be omitted in early T1/T2 tumors. OM was associated with poor prognosis, increased peritoneal recurrence, and decreased overall survival, in spite of a complete omentectomy, and may serve as a prognostic indicator for disease recurrence and overall survival.

Peritoneal resident macrophages in tumor metastasis and immunotherapy

Macrophages residing in various tissues play crucial roles in innate immunity, tissue repair, and immune homeostasis. The development and differentiation of macrophages in non-lymphoid tissues are highly regulated by the tissue microenvironment. Peritoneum provides a unique metastatic niche for certain types of tumor cells. As the dominant immune cell type in peritoneal cavity, macrophages control the immune response to tumor and influence the efficacy of anti-tumor therapy. Considering the heterogeneity of macrophages in origin, metabolism, and function, it is always challenging to define the precise roles of macrophages in tumor microenvironment. We review here recent progresses in peritoneal resident macrophage research in the context of physiological and metastatic tumor conditions, which may benefit the development of new anti-tumor therapies through targeting macrophages.

Partial omentectomy maybe practicable for T3 or shallower gastric cancer patients

BACKGROUND

Total omentectomy is often performed with gastrectomy as radical surgery for gastric cancer (GC) patients. However, it remains controversial whether GC patients can benefit from omentectomy. The aim of this study was to analyze the incidence and clinical significance of tumor deposits (TDs) in different anatomical subregions of perigastric omentum in GC patients undergoing gastrectomy with total omentectomy.

METHODS

From October 2011 to December 2013, 1253 patients who underwent gastrectomy with total omentectomy for GC were retrospective reviewed. The TDs in different anatomical subregions of perigastric omentum were examined.

RESULTS

Of 1253 patients, TDs positivity was 11.2%. Tumor deposits in the omentum of greater curvature and in the omentum of lesser curvature were associated with lymphovascular invasion, perineural invasion, advanced tumor node metastasis stages, and unfavorable survival. Besides, TDs in the proximal omentum of greater curvature and in the omentum of lesser curvature correlated with older patients and larger tumors. Kaplan-Meier curves showed that patients with TDs had worser overall survival (OS) than those without, regardless of TD positions. Patients with TDs in the omentum of greater curvature had the worst prognosis, followed by patients with TDs in the omentum of lesser curvature and patients with no TDs. Tumor deposits in the proximal omentum of greater curvature was an independent prognostic factor for OS. Moreover, only patients classified as pT4 had TDs in the distal omentum of greater curvature.

CONCLUSIONS

Patients with TDs in the omentum of greater curvature had the worst prognosis, followed by patients with TDs in the omentum of lesser curvature and patients with no TDs. In addition, partial omentectomy might be practicable for gastric cancer patients classified as T3 or shallower tumors.

Circulating Tregs accumulate in omental tumors and acquire adipose-resident features

Tumors that metastasize in the peritoneal cavity typically end up in the omental adipose tissue, a particularly immune-suppressive environment that includes specialized adipose-resident regulatory T cells (Tregs). Tregs rapidly accumulate in the omentum after tumor implantation and potently suppress anti-tumor immunity. However, it is unclear whether these Tregs are recruited from the circulation or derived from pre-existing adipose-resident Tregs by clonal expansion. Here we show that Tregs in tumor-bearing omenta predominantly have thymus-derived characteristics. Moreover, naïve tumor antigen-specific CD4+ T cells fail to differentiate into Tregs in tumor-bearing omenta. In fact, Tregs derived from the pre-tumor repertoire are sufficient to suppress anti-tumor immunity and promote tumor growth. However, tumor implantation in the omentum does not promote Treg clonal expansion, but instead leads to increased clonal diversity. Parabiosis experiments show that despite tissue-resident (non-circulating) characteristics of omental Tregs in naïve mice, tumor implantation promotes a rapid influx of circulating Tregs, many of which come from the spleen. Finally, we show that newly recruited Tregs rapidly acquire characteristics of adipose-resident Tregs in tumor-bearing omenta. These data demonstrate that most Tregs in omental tumors are recruited from the circulation and adapt to their environment by altering their homing, transcriptional and metabolic properties.

Lymphocyte and macrophage infiltration in omental metastases indicates poor prognosis in advance stage epithelial ovarian cancer

Objective

To investigate the prognostic value of immune cells within omental metastases originating from advanced epithelial ovarian cancer (EOC).

Methods

We performed immunohistochemical analysis to determine the levels of CD4+/CD8+ tumor-infiltrating lymphocytes (TILs) and CD68+ tumor-associated microphages (TAMs) in omental specimens from 100 patients with advanced EOC. Significant prognostic factors, including immune cells and clinical parameters, were assessed by Kaplan–Meier survival analysis and Cox models.

Results

Cox regression analysis showed that elevated levels of CD68+ TAMs and intra-islet CD4+ TILs in omental metastases were the main risk factors associated with worse survival outcomes for advanced EOC. Moreover, the survival analysis of relationships between omental immune cells and favorable clinical predictors revealed additional prognostic stratification information.

Conclusion

Omental immune cells (TAMs and TILs) provide alternative prognostic factors in advanced EOC. In contrast to markers of the EOC tumor microenvironment at the primary site, elevated CD68+ TAMs and intra-islet CD4+ TILs in omental metastases serve as negative prognostic markers in advanced EOC and imply an unfavorable outcome.

Gastrectomy with omentum preservation versus gastrectomy with omentectomy for locally advanced gastric cancer: A systematic review and meta-analysis

BACKGROUND

Omentectomy has been traditionally a part of standard radical gastrectomy. Its clinical benefit for locally advanced gastric cancer (LAGC) remains controversial. This study aimed at evaluating the impact of gastrectomy with omentum preservation (GOP) on survival, recurrence, surgical outcomes and postoperative complications by comparing with gastrectomy with omentum resection (GOR).

METHODS

Original studies comparing GOP with GOR in LAGC were searched. Meta-analysis was performed using RevMan 5.4.

RESULTS

Seven studies involving 1879 patients were analyzed. Compared with GOR, GOP achieved significantly better overall survival (HR = 0.75 [0.60, 0.95], P = 0.01), with similar relapse-free survival (HR = 0.84 [0.68, 1.03], P = 0.10). The two groups had similar total recurrence rate (OR = 0.86 [0.68, 1.08], P = 0.19) and no significant differences in rates of peritoneal, hematogenous, locoregional or distant lymph node recurrences. GOP had significantly less blood loss (MD = -83 [-139, -28] ml, P = 0.003) and tended to have shorter operation time (MD = -28 [-58, 2] min, P = 0.06), with similar harvested number of lymph nodes (MD = -0.4 [-2.6, 1.8], P = 0.70). The incidences of total all grade and major complications were similar in GOP and GOR (all grade: 31.8% vs. 30.3%, OR = 1.08 [0.79, 1.46], P = 0.64; major: 9.2% vs. 10.1%, OR = 1.14 [0.55, 2.34], P = 0.73). There were no significant differences in incidences of complication or postoperative mortality.

CONCLUSIONS

Omentum preservation did not affect curability or survival in LAGC. These findings require validation in randomized controlled trials with large sample sizes.

Gastrectomy with or without omentectomy for gastric cancer: A systematic review and meta-analysis

BACKGROUND

Omentectomy is conventionally performed in the procedure of gastrectomy for gastric cancer. However, the clinical value and importance of omentectomy remain unclear. This meta-analysis investigated the benefits and safety of gastrectomy with or without omentectomy for patients with gastric cancer.

METHODS

A literature search was conducted in PubMed, Embase, and the Cochrane Library for studies comparing complete omentectomy with omentum preservation or partial omentectomy. Primary outcomes were overall survival, relapse-free survival, and incidences of recurrence and complications, whereas secondary outcomes were the total length of operation and the amount of blood loss.

RESULTS

Nine studies involving 3,561 patients were included. Our meta-analysis revealed no significant differences between omentectomy and omentum preservation in terms of the 5-year overall survival (risk ratio [RR] = 0.95, 95% confidence interval [CI] = 0.89-1.01), 5-year relapse free survival (RR: 0.96, 95% CI: 0.89-1.03), incidence of recurrence in the peritoneum or other visceral organs (RR: 1.13, 95% CI: 0.80-1.60 and RR: 1.06, 95% CI: 0.78-1.45, respectively), and incidence of complications (RR: 1.15, 95% CI: 0.89-1.50). Moreover, omentum preservation significantly reduced the total length of operation (mean difference [MD] 25.70, 95% CI: 3.23-48.17) and the amount of blood loss (MD: 56.29, 95% CI: 14.02-98.56).

CONCLUSION

Omentectomy may not be necessary and can be omitted during gastrectomy for gastric cancer.

Characterizing the tumor microenvironment of metastatic ovarian cancer by single-cell transcriptomics

Understanding the cellular composition of the tumor microenvironment and the interactions of the cells is essential to the development of successful immunotherapies in cancer. We perform single-cell RNA sequencing (scRNA-seq) of 9,885 cells isolated from the omentum in 6 patients with ovarian cancer and identify 9 major cell types, including cancer, stromal, and immune cells. Transcriptional analysis of immune cells stratifies our patient samples into 2 groups: (1) high T cell infiltration (high T_inf) and (2) low T cell infiltration (low T_inf). TOX-expressing resident memory CD8⁺ T (CD8⁺ Trm) and granulysin-expressing CD4⁺ T cell clusters are enriched in the high T_inf group. Concurrently, we find unique plasmablast and plasma B cell clusters, and finally, NR1H2⁺IRF8⁺ and CD274⁺ macrophage clusters, suggesting an anti-tumor response in the high T_inf group. Our scRNA-seq study of metastatic tumor samples provides important insights in elucidating the immune response within ovarian tumors.

Omentum preservation as an oncologically comparable and surgically superior alternative to total omentectomy during radical gastrectomy for T3-T4 gastric cancer

BACKGROUND

Total omentectomy has conventionally been performed and has been regarded as standard procedure in radical gastrectomy for cancer. However, omentum preservation is the preferred procedure during minimally invasive surgery, without sufficient evidence of oncological safety, especially for T3-T4 gastric cancer.

METHOD

A total of 3,510 patients who underwent radical gastrectomy for T3-T4 gastric cancer between January 2003 and December 2015 were reviewed, retrospectively. After propensity score matching, 225 patients in the omentum preservation group were compared with 225 patients in the total omentectomy group. The primary outcome was 5-year overall survival.

RESULTS

The omentum preservation group showed significantly shorter operation time (P = .001) and less blood loss (P = .004) than the total omentectomy group. Shorter operation time was also observed with both open and minimally invasive approaches (P < .001 and P = .007, respectively). The 5-year overall survival rates were 75.4% for the omentum preservation group and 72.6% for the total omentectomy group (log-rank P = .06; hazard ratio 0.7 [95% confidence interval, 0.48-1.01]). The 5-year relapse-free survival was higher in the omentum preservation group (73.8%) than in the total omentectomy group (66.1%), without statistical significance (log-rank P = .09; hazard ratio 0.74 [95% confidence interval, 0.52-1.06]).

CONCLUSION

Regardless of the surgical approach, omentum preservation provided comparable oncologic outcomes with better surgical outcomes, suggesting that this could be an acceptable alternative to total omentectomy for T3-T4 gastric cancer. These findings warrant further investigation in randomized clinical trials.

Short-Term Outcomes from a Randomized Screening Phase II Non-inferiority Trial Comparing Omentectomy and Omentum Preservation for Locally Advanced Gastric Cancer: the TOP-G Trial

BACKGROUND

Omentectomy is considered an essential part of curative gastrectomy for locally advanced gastric cancer (GC), albeit without solid evidence. We conducted a randomized phase II trial (the TOP-G trial) comparing omentectomy and omentum preservation for gastric cancer. This report describes the short-term findings regarding the trial's secondary endpoints.

METHODS

The trial protocol was submitted to the University Hospital Medical Information Network Clinical Trials Registry ( http://www.umin.ac.jp/ctr/ : UMIN000005421). The key eligibility criteria were histologically confirmed cT2-4a and N0-2 gastric adenocarcinoma. Short-term surgical outcomes, including morbidity and mortality, were compared between the omentectomy group (group A, control arm) and the omentum-preserving surgery group (group B, test arm). All procedures were performed via an open approach. Based on a non-inferiority margin of 7%, statistical power of 0.7, and type I error of 0.2, the sample size was set to 250 patients.

RESULTS

A total of 251 patients were eligible and randomized (group A: 125 patients, group B: 126 patients) between April 2011 and October 2018. After excluding patients who had peritoneal metastasis or laparotomy history, safety outcomes were analyzed for 247 patients. Group A had a significantly longer median operation time (225 min vs. 204 min, p = 0.022) and tended to have greater median blood loss (260 mL vs. 210 mL p = 0.073). The incidences of morbidity were similar and < 10% in both groups (8% vs. 9%, p = 1.000). There was no mortality in either group.

CONCLUSIONS

Operative risk was generally similar between omentectomy and omentum-preserving surgery for locally advanced gastric cancer.

Long-term outcomes of omentum-preserving versus resecting gastrectomy for locally advanced gastric cancer with propensity score analysis

Omentectomy is conducted for advanced gastric cancer (AGC) patients as radical surgery without an adequate discussion of the effect. This study was conducted to reveal the impact of omentum-preserving gastrectomy on postoperative outcomes. AGC patients with cT3 and 4 disease who underwent total or distal gastrectomy with R0 resection were identified retrospectively. They were divided into the omentum-preserved group (OPG) and the omentum-resected group (ORG) and matched with propensity score matching with multiple imputation for missing values. Three-year overall survival (OS) and 3-year relapse-free survival (RFS) were compared, and the first recurrence site and complications were analysed. The numbers of eligible patients were 94 in the OPG and 144 in the ORG, and after matching, the number was 73 in each group. No significant difference was found in the 3-year OS rate (OPG: 78.9 vs. ORG: 78.9, P = 0.54) or the 3-year RFS rate (OPG: 77.8 vs. ORG: 68.2, P = 0.24). The proportions of peritoneal carcinomatosis and peritoneal dissemination as the first recurrence site and the rate and severity of complications were similar in the two groups. Omentectomy is not required for radical gastrectomy for AGC.

Specialized immune responses in the peritoneal cavity and omentum

The peritoneal cavity is a fluid filled space that holds most of the abdominal organs, including the omentum, a visceral adipose tissue that contains milky spots or clusters of leukocytes that are organized similar to those in conventional lymphoid tissues. A unique assortment of leukocytes patrol the peritoneal cavity and migrate in and out of the milky spots, where they encounter Ags or pathogens from the peritoneal fluid and respond accordingly. The principal role of leukocytes in the peritoneal cavity is to preserve tissue homeostasis and secure tissue repair. However, when peritoneal homeostasis is disturbed by inflammation, infection, obesity, or tumor metastasis, specialized fibroblastic stromal cells and mesothelial cells in the omentum regulate the recruitment of peritoneal leukocytes and steer their activation in unique ways. In this review, the types of cells that reside in the peritoneal cavity, the role of the omentum in their maintenance and activation, and how these processes function in response to pathogens and malignancy will be discussed.

Gastrectomy with or without omentectomy for cT3–4 gastric cancer: a multicentre cohort study

Background

Omentectomy is performed widely for locally advanced gastric cancer to prevent disease recurrence. However, its clinical benefit is unknown.

Methods

This retrospective cohort study compared the outcome of gastrectomy with preservation of the omentum (GPO) and gastrectomy with resection of the omentum (GRO) among patients with cT3–T4 gastric cancer who underwent gastrectomy between 2006 and 2012 in one of five participating institutions. A consensus conference identified 28 variables potentially associated with outcome after gastrectomy for the estimation of propensity scores, and propensity score matching (PSM) was undertaken to control for possible confounders. Postoperative surgical outcomes, overall survival and disease recurrence were compared between GPO and GRO.

Results

A total of 1758 patients were identified, of whom 526 remained after PSM, 263 in each group. Median follow-up was 4·9 (i.q.r. 3·1–5·9) years in the GRO group and 5·0 (2·5–6·8) years in the GPO group. The incidence of postoperative complications of Clavien–Dindo grade III or more was significantly higher in the GRO group (17·5 versus 10·3 per cent; P = 0·016). Five-year overall survival rates were 77·1 per cent in the GRO group and 79·4 per cent in the GPO group (P = 0·749). There were no significant differences in recurrence rate or pattern of recurrence between the groups.

Conclusion

Overall survival and disease recurrence were comparable in patients with cT3–4 gastric cancer who underwent GPO or GRO.

Long term oncological outcome of patients with grossly early gastric cancer-mimicking advanced gastric cancer

BACKGROUND

The survival of grossly early gastric cancer-mimicking advanced gastric cancer (EGC-mimicking AGC) patients had not been investigated. We evaluated the prognosis of patients who were diagnosed as early gastric cancer before surgery and advanced gastric cancer after surgery.

METHODS

This retrospective study reviewed 3592 gastric cancer patients who had radical surgery from January 2007 to February 2015. We used a 1:2 propensity score matching method for the analysis. The matching factors were age, sex, body mass index and the depth of cancer invasion. The 5-year overall survival (OS) and disease-free survival (DFS) of the two study groups were analyzed.

RESULTS

The 475 grossly EGC-mimicking AGC patients were matched to 910 Borrmann type advanced gastric cancer (AGC) patients. The 5-year OS and DFS of the EGC-mimicking AGC patients were significantly higher than the Borrmann type AGC patients, (89.2% versus 83.4%, p = 0.025; 93.0% versus 85.6%, p < 0.001, respectively). The proportion of patients with lymph node (LN) metastasis was 45.5% in the EGC-mimicking AGC group and 57.1% in the Borrmann type AGC patients (p < 0.001). The ratio of metastatic LNs of N1 and N2 station was 5.2% and 3.1%, respectively, in EGC-mimicking AGC patients; this was lower than in Borrmann type AGC patients (N1: 8.9%, p < 0.001; N2: 3.7%, p = 0.308).

CONCLUSIONS

Patients with grossly EGC-mimicking AGC had better prognosis than patients with the Borrmann type AGC due to fewer LN metastases. This suggests that limited LN dissection of EGC-mimicking AGC patients may be feasible.

Laparoscopic Surgery of Gastric Cancer with D2 Lymphadenectomy and Omentum Preservation: Our 10 Years Experience

Introduction: The debate is still open about laparoscopic treatment of gastric cancer. The aim of this retrospective study is to analyze our short-, medium-, and long-term surgical and oncological results in laparoscopic treatment of gastric cancer with D2 lymphadenectomy and omentum preservation. Materials and Methods: From January 2010 to June 2018, after >150 surgical procedures for gastric cancer performed by minimally invasive approach, we performed 100 laparoscopic subtotal gastrectomies and 38 total gastrectomies, both for early gastric cancer (EGC) and advanced gastric cancer (AGC). We always made a D2 lymphadenectomy or higher. As often as possible, we performed omentum-preserving technique. Primary outcomes analyzed included incidence of medical and surgical complications. Secondary outcomes analyzed were survival probability and incidence of relapse. Every patient read and signed informed consent before surgery. Results: Mean operative time: 2.4 ± 0.7 hours (range 1.2-4.7 hours). Rate of conversions: 14.5% (20/138); intraoperative complications: 1.4% (2/138) and positive resection margins: 6.5% (9/138). Overall incidence of duodenal fistula: 3.6% (5/138). Rate of reoperation was 7.3% (10/138). Postoperative complications according to Clavien-Dindo classification: I 3.6% (5/138); II 13.0% (18/138); III 5.8% (8/138); III B 0.7% (1/138); V 1.4% (2/138). Overall survival with 60 months follow-up was 58%. Overall 60 months incidence of relapse was 44%. Patients with omentum preservation had a lower incidence of relapse than patients with omentectomy (40% versus 57% P = .002). Conclusions: Laparoscopic treatment of gastric cancer with D2 lymphadenectomy and omentum preservation is safe and feasible, both for EGC and for AGC. Although this study has limitations, omentum-preserving technique was associated with a statistically lower recurrence rate.

Foliate Lymphoid Aggregates as Novel Forms of Serous Lymphocyte Entry Sites of Peritoneal B Cells and High-Grade B Cell Lymphomas

The cellular homeostasis of lymphoid tissues is determined by the continuous interactions of mobile hematopoietic cells within specialized microenvironments created by sessile stromal cells. In contrast to the lymph nodes and mucosal lymphoid tissues with well-defined entry and exit routes, the movement of leukocytes in the peritoneal cavity is largely unknown. In this study, we report that, in addition to the omental milky spots and fat-associated lymphoid clusters, in mice, the serous surface of the mesenteric adipose streaks contains lymphocyte-rich organoids comprised of a highly compacted leaf-like part connected to the adipose tissue that can also efficiently bind B cells and high-grade B cell lymphoma (diffuse large B cell lymphoma) cells. Denoted as foliate lymphoid aggregates (FLAgs), these structures show incomplete T/B segregation and a partially differentiated stromal architecture. LYVE-1-positive macrophages covering FLAgs efficiently bind i.p. injected normal B cells as well as different types of diffuse large B cell lymphoma cells. Within FLAgs, the lymphocytes compartmentalize according to their chemokine receptor pattern and subsequently migrate toward the mesenteric lymph nodes via the mesenteric lymphatic capillaries. The blood supply of FLAgs includes short vascular segments displaying peripheral lymph node addressin, and the extravasation of lymphocytes to the omental and mesenteric adipose tissues is partly mediated by L-selectin. The appearance of i.p. injected cells in mesenteric lymph nodes suggests that the mesentery-associated lymphatics may also collect leukocytes from the fat-associated lymphoid clusters and FLAgs, thus combining the mucosal and serous exit of mobile leukocytes and increasing the range of drainage sites for the peritoneal expansion of lymphoid malignancies.

The role of omentectomy in the surgical treatment of uterine serous carcinoma

OBJECTIVE

The aims of this study were to assess the role of omentectomy in the staging of uterine serous carcinoma (USC) and to evaluate its impact on patient outcomes.

STUDY DESIGN

Patients diagnosed with USC at the First Affiliated Hospital of Sun Yat-sen University of China were retrospectively reviewed. The clinicopathological characteristics and survival data of 187 patients were analyzed. Risk factors for omental metastasis were evaluated. Kaplan-Meier survival curves were used to compare survival status and the presence of omental metastasis.

RESULTS

We found that 35 of 187 patients (18.7%) had omental metastases. Omental metastasis was significantly associated with adnexal involvement (40.0% vs 19.1%, P = 0.008, OR 2.828, 95% CI 1.286-6.218). Multivariate analysis showed that in addition to lymph node metastases and suboptimal surgery, omental metastasis in USC remained an independent predictor of decreased PFS and OS (PFS, HR 1.48, 95% CI 1.14-4.63, P = 0.024; OS, HR 1.39, 95% CI 1.04-3.60, P = 0.043).

CONCLUSIONS

The incidence of omental metastasis is not low in patients with USC. Visual assessment and omental biopsy may be insufficient for recognizing occult metastases. Omentectomy should be part of the staging surgery in USC patients because it provides additional information about survival. Prospective studies are needed to confirm these results.

TOTAL OMENTECTOMY IN GASTRIC CANCER SURGERY: IS IT ALWAYS NECESSARY?

BACKGROUND

Traditionally, total omentectomy is performed along with gastric resection and extended lymphadenectomy in gastric cancer (GC) surgery. However, solid evidences regarding its oncologic benefit is still scarce.

AIM

To evaluate the incidence of metastatic omental lymph nodes (LN) in patients undergoing curative gastrectomy for GC, as well as its risk factors and patients' outcomes.

METHODS

All consecutive patients submitted to D2/modified D2 gastrectomy due to gastric adenocarcinoma from March 2009 to April 2016 were retrospectively reviewed from a prospective collected database.

RESULTS

Of 284 patients included, five (1.8%) patients had metastatic omental LN (one: pT3N3bM0; two: pT4aN3bM0; one: pT4aN2M0 and one pT4bN3bM0). Four of them deceased and one was under palliative chemotherapy due relapse. LN metastases in the greater omentum significantly correlated with tumor's size (p=0.018), N stage (p<0.001), clinical stage (p=0.022), venous invasion growth (p=0.003), recurrence (p=0.006), site of recurrence (peritoneum: p=0.008; liver: p=0.023; ovary: p=0.035) and death (p=0.008).

CONCLUSION

The incidence of metastatic omental LN of patients undergoing radical gastrectomy due to GC is extremely low. Total omentectomy may be avoided in tumors smaller than 5.25 cm and T1/T2 tumors. However, the presence of lymph node metastases in the greater omentum is associated with recurrence in the peritoneum, liver, ovary and death.

The Tumor Microenvironment of Epithelial Ovarian Cancer and Its Influence on Response to Immunotherapy

Immunotherapy as a treatment for cancer is a growing field of endeavor but reports of success have been limited for epithelial ovarian cancer. Overcoming the challenges to developing more effective therapeutic approaches lies in a better understanding of the factors in cancer cells and the surrounding tumor microenvironment that limit response to immunotherapies. This article provides an overview of some ovarian cancer cell features such as tumor-associated antigens, ovarian cancer-derived exosomes, tumor mutational burden and overexpression of immunoinhibitory molecules. Moreover, we describe relevant cell types found in epithelial ovarian tumors including immune cells (T and B lymphocytes, Tregs, NK cells, TAMs, MDSCs) and other components found in the tumor microenvironment including fibroblasts and the adipocytes in the omentum. We focus on how those components may influence responses to standard treatments or immunotherapies.

The Tumor Microenvironment of Epithelial Ovarian Cancer and Its Influence on Response to Immunotherapy

Immunotherapy as a treatment for cancer is a growing field of endeavor but reports of success have been limited for epithelial ovarian cancer. Overcoming the challenges to developing more effective therapeutic approaches lies in a better understanding of the factors in cancer cells and the surrounding tumor microenvironment that limit response to immunotherapies. This article provides an overview of some ovarian cancer cell features such as tumor-associated antigens, ovarian cancer-derived exosomes, tumor mutational burden and overexpression of immunoinhibitory molecules. Moreover, we describe relevant cell types found in epithelial ovarian tumors including immune cells (T and B lymphocytes, Tregs, NK cells, TAMs, MDSCs) and other components found in the tumor microenvironment including fibroblasts and the adipocytes in the omentum. We focus on how those components may influence responses to standard treatments or immunotherapies.

The Tumor Microenvironment of Epithelial Ovarian Cancer and Its Influence on Response to Immunotherapy

Immunotherapy as a treatment for cancer is a growing field of endeavor but reports of success have been limited for epithelial ovarian cancer. Overcoming the challenges to developing more effective therapeutic approaches lies in a better understanding of the factors in cancer cells and the surrounding tumor microenvironment that limit response to immunotherapies. This article provides an overview of some ovarian cancer cell features such as tumor-associated antigens, ovarian cancer-derived exosomes, tumor mutational burden and overexpression of immunoinhibitory molecules. Moreover, we describe relevant cell types found in epithelial ovarian tumors including immune cells (T and B lymphocytes, Tregs, NK cells, TAMs, MDSCs) and other components found in the tumor microenvironment including fibroblasts and the adipocytes in the omentum. We focus on how those components may influence responses to standard treatments or immunotherapies.

Mechanisms of peritoneal dissemination in gastric cancer

Peritoneal dissemination is the most frequent metastatic pattern of gastric cancer, but the mechanisms underlying peritoneal dissemination are yet to be elucidated. Paget's 'seed and soil' hypothesis is recognized as the fundamental theory of metastasis. The 'seeding' theory proposes that the formation of peritoneal dissemination is a multistep process, including detachment from the primary tumour, transmigration and attachment to the distant peritoneum, invasion into subperitoneal tissue and proliferation with blood vascular neogenesis. In the present review, the progress of each step is discussed. Milky spots, as a lymphatic apparatus, are indicative of lymphatic orifices on the surface of the peritoneum. These stomata are open gates for peritoneal-free cancer cells to migrate into the submesothelial space. Therefore, milky spots provide suitable 'soil' for cancer cells to implant. Other theories have also been proposed to clarify the peritoneal dissemination process, including the transvessel metastasis theory, which suggests that the peritoneal metastasis of gastric cancer develops via a vascular network mediated by hypoxia inducible factor-1α.

Immunological Functions of the Omentum

The omentum is a visceral adipose tissue with unique immune functions. Although it is primarily an adipose tissue, the omentum also contains lymphoid aggregates, called milky spots (MSs), that contribute to peritoneal immunity by collecting antigens, particulates, and pathogens from the peritoneal cavity and, depending on the stimuli, promoting a variety of immune responses, including inflammation, tolerance, or even fibrosis. Reciprocal interactions between cells in the MS and adipocytes regulate their immune and metabolic functions. Importantly, the omentum collects metastasizing tumor cells and supports tumor growth by immunological and metabolic mechanisms. Here we summarize our current knowledge about the development, organization, and function of the omentum in peritoneal immunity.

Role of omentectomy as part of radical surgery for gastric cancer

Background

A complete omentectomy is recommended as part of radical (sub)total gastrectomy for gastric cancer, but there is little evidence to suggest any survival benefit. The aim of this study was to evaluate the incidence of, and risk factors for, metastases in the greater omentum in patients undergoing gastrectomy for gastric cancer.

Methods

This was a multicentre prospective cohort study (OMEGA trial) of consecutive patients with gastric cancer undergoing (sub)total gastrectomy with complete en bloc omentectomy and modified D2 lymphadenectomy. After resection, the omentum was separated from the gastrectomy specimen distal to the gastroepiploic vessels and sent separately for pathological examination. The primary endpoint was the presence of metastases in the greater omentum.

Results

Of 100 included patients, five (5·0 per cent) had metastases in the greater omentum. Pathology results showed advanced tumours in all five (pT4b N1 M1, pT4b N2 M1, ypT4a N1 M1, ypT3 N2 M0, ypT3 N3 M0). The resection was microscopically non-radical at the proximal (3) or distal (2) resection margin in all of these patients. Metastases in the greater omentum correlated significantly with a microscopically non-radical resection, tumour expansion in the oesophagus or duodenum, linitis plastica or a proximal gastric tumour with diameter of at least 5 cm, stage III–IV disease and (y)pM1 category.

Conclusion

In resectable gastric cancer, the incidence of metastases in the greater omentum is low, and when present associated with advanced disease and non-radical features. Thus, omentectomy as part of a radical gastrectomy may be omitted. Registration number: NCT02050659 (http://www.clinicaltrials.gov).

Animal models of colorectal peritoneal metastasis

Colorectal cancer remains an important cause of mortality worldwide. The presence of peritoneal carcinomatosis (PC) causes significant symptoms and is notoriously difficult to treat. Therefore, informative preclinical research into the mechanisms and possible novel treatment options of colorectal PC is essential in order to improve the prognostic outlook in these patients. Several syngeneic and xenograft animal models of colorectal PC were established, studying a wide range of experimental procedures and substances. Regrettably, more sophisticated models such as those giving rise to spontaneous PC or involving genetically engineered mice are lacking. Here, we provide an overview of all reported colorectal PC animal models and briefly discuss their use, strengths, and limitations.

Milky spots: omental functional units and hotbeds for peritoneal cancer metastasis

As the most common metastatic disease of abdomen pelvic cavity cancer, peritoneal carcinomatosis (PC) renders significant negative impact on patient survival and quality of life. Invasive peritoneal exfoliated cancer cells (PECCs) preferentially select the omentum as a predominant target site for cancer cell colonization and proliferation compared with other tissues in the abdominal cavity. The precise pathogenic mechanism remains to be determined. As omental milky spots (MSs) are the major implantation site for malignant cells in peritoneal dissemination, researches on mechanisms of PC have been mainly focused on MS, primitive lymphoid tissues with unique structural features, and functional characteristics. To date, extensive biophysical and biochemical methods have been manipulated to investigate the MS exact function in the peritoneal cavity. This review summarized MS as hotbeds for PECC. The anatomical distribution was briefly described first. Then, MS histology was systematically reviewed, including morphological features, cellular constituents, and histological staining methods. At last, the roles of MS in PC pathological process were summarized with special emphasis on the distinct roles of macrophages.

Peritoneal Dissemination Requires an Sp1-Dependent CXCR4/CXCL12 Signaling Axis and Extracellular Matrix-Directed Spheroid Formation

Peritonitis carcinomatosa is an advanced and intractable state of gastrointestinal and ovarian cancer, where mechanistic elucidation might enable the development of more effective therapies. Peritoneal dissemination of this type of malignancy has been generally thought to initiate from "milky spots" of primitive lymphoid tissues in the peritoneal cavity. In this study, we offer evidence challenging this idea, based on the finding that tumor implantation and directional dissemination was not required for the presence of milky spots, but rather SCF/CXCL12-expressing niche-like cells located at the border regions of perivascular adipose tissue. Interestingly, we found that peritoneal cavity lavage fluid, which specifically contains peritoneal collagen type IV and plasma fibronectin, dramatically facilitated spheroid formation of murine and human colon cancer cells. Spheroid formation strongly induced the expression of CXCR4 in an Sp1-dependent manner to promote niche-directed metastasis. Notably, disrupting sphere formation or inhibiting Sp1 activity was sufficient to suppress tumor dissemination and potentiated chemosensitivity to 5-fluorouracil. Our findings illuminate mechanisms of peritoneal cancer dissemination and highlight the Sp1/CXCR4/CXCL12 signaling axis as a rational target for the development of therapeutics to manage this intractable form of malignancy.

Peritoneal milky spots serve as a hypoxic niche and favor gastric cancer stem/progenitor cell peritoneal dissemination through hypoxia-inducible factor 1α

Peritoneal dissemination is the most common cause of death in gastric cancer patients. The hypoxic microenvironment plays a major role in controlling the tumor stem cell phenotype and is associated with patients' prognosis through hypoxia-inducible factor-1α (HIF-1α), a key transcriptional factor that responds to hypoxic stimuli. During the peritoneal dissemination process, gastric cancer stem/progenitor cells (GCSPCs) are thought to enter into and maintained in peritoneal milky spots (PMSs), which have hypoxic microenvironments. However, the mechanism through which the hypoxic environment of PMSs regulated GCSPC maintenance is still poorly understood. Here, we investigated whether hypoxic PMSs were an ideal cancer stem cell niche suitable for GCSPC engraftment. We also evaluated the mechanisms through which the HIF-1α-mediated hypoxic microenvironment regulated GCSPC fate. We observed a positive correlation between HIF-1α expression and gastric cancer peritoneal dissemination (GCPD) in gastric cancer patients. Furthermore, the GCSPC population expanded in primary gastric cancer cells under hypoxic condition in vitro, and hypoxic GCSPCs showed enhanced self-renewal ability, but reduced differentiation capacity, mediated by HIF-1α. In an animal model, GCSPCs preferentially resided in the hypoxic zone of PMSs; moreover, when the hypoxic microenvironment in PMSs was destroyed, GCPD was significantly alleviated. In conclusion, our results demonstrated that PMSs served as a hypoxic niche and favored GCSPCs peritoneal dissemination through HIF-1α both in vitro and in vivo. These results provided new insights into the GCPD process and may lead to advancements in the clinical treatment of gastric cancer.

Microscopic Omental Metastasis in Clinical Stage I Endometrial Cancer: A Meta-analysis

BACKGROUND

A patient with early-stage endometrial cancer may possibly have microscopic metastasis in the omentum, which is associated with a poor prognosis. The purpose of this study was to identify risk factors for microscopic omental metastasis in patients with clinical stage I endometrial cancer to establish the indications for selective omentectomy.

METHODS

We searched the PubMed, EMBASE, and Cochrane Library databases for published studies from inception to August 2014, using terms such as 'endometrial cancer' or 'uterine cancer' for disease, 'omentectomy' or 'omental biopsy' for intervention, and 'metastasis' for outcome. Two reviewers independently identified the studies that matched the selection criteria. We calculated the pooled risk ratios (RRs) with 95 % confidence intervals (CI) of each surgicopathologic finding for microscopic omental metastases in clinical stage I endometrial cancer. We also calculated the prevalence of microscopic omental metastases.

RESULTS

Among 1163 patients from ten studies, 22 cases (1.9 %) of microscopic omental metastases were found, which accounted for 26.5 % of all omental metastases. Positive lymph nodes (RR 8.71, 95 % CI 1.38-54.95), adnexal metastases (RR 16.76, 95 % CI 2.60-107.97), and appendiceal implants (RR 161.67, 95 % CI 5.16-5061.03) were highly associated with microscopic omental metastases.

CONCLUSIONS

Microscopic omental metastases were not negligible in patients with clinical stage I endometrial cancer. Those with a risk factor of microscopic omental metastases were recommended for selective omentectomy.

The role of the CCL22-CCR4 axis in the metastasis of gastric cancer cells into omental milky spots

Background

The omentum is one of the initial sites for peritoneal metastasis because it possesses milky spots that provide a microenvironment for cancer cells to readily migrate and grow into micrometastases. This study investigated the role of the CCL22-CCR4 axis in gastric cancer cells selectively infiltrating into milky spots.

Methods

Gastric cancer MFC cells labelled with DiI were injected intraperitoneally into strain 615 mice. The mice were euthanised at specified intervals and the omentum was excised for immunohistochemistry. The effects of CCL22 on the proliferation and migration of MFCs were assessed by MTT and trans-well assays. RT-PCR and Western blot analysis detected CCR4 mRNA and protein expression levels in MFCs. Immunohistochemistry was used to analyse CCL22 and CCR4 expression in the milky spot micrometastases.

Results

Two weeks after intraperitoneal injection, the milky spot areas were completely occupied by proliferating gastric cancer cells and cell cluster-type micrometastases were observed. In contrast, cancer cells formed single cell-type micrometastases in the non-milky spot areas. MFCs expressed CCR4, which was localised on the cell surface and or in the cytoplasm. Different concentrations of CCL22 significantly increased the proliferation ability of MFCs. Additionally, concentrations of CCL22 between 10–100 ng/ml significantly increased the migration of MFCs. Within omental milky spots, CCL22 was localised mainly on the cell surface and or in the cytoplasm. Within sections of omental milky spot micrometastases, CCR4 was recognised on or in gastric cancer cells, constituent cells milky spots, blood cells and blood endothelial cells.

Conclusions

Omental milky spots are a congenial microenvironment for peritoneal free gastric cancer cells to migrate, survive, and establish cell cluster-type metastases. The CCL22-CCR4 axis contributes to this selective infiltration process.

Lethal effect of a hyperthermic CO₂ pneumoperitoneum on gastric cancer cells

OBJECTIVES

We investigated the lethal effect of a hyperthermic CO₂ pneumoperitoneum on gastric cancer cells. This could form the theoretical basis for further studies of the feasibility and safety of inflating hyperthermic CO₂ in the abdominal cavity of gastric cancer patients during laparoscopy.

METHODS

An in vitro hyperthermic CO₂ pneumoperitoneum experimental model was built, where gastric cancer cell line SGC-7901 cells were grouped according to temperature. Cytotoxicity was detected using a cell counting kit; apoptosis was detected by Annexin V-FITC/PI flow cytometry and Hoechst 33342/PI fluorescent microscopy. Morphological alterations were observed by transmission electron microscopy. Invasion and migration were detected by a scratch test and by transwell migration, respectively.

RESULTS

Cytotoxicity assays showed that a hyperthermic CO₂ pneumoperitoneum significantly inhibited the proliferation of SGC-7901 cells (P<0.05); it also significantly induced apoptosis of SGC-7901 cells (P<0.05). Morphological observations showed that the cell membrane and nucleus had an apoptotic phenotype. The invasiveness and migration ability of the gastric cancer cells subjected to hyperthermic CO₂ were significantly reduced.

CONCLUSIONS

A hyperthermic CO₂ pneumoperitoneum had a lethal effect on gastric cancer SGC-7901 cells by inhibiting their invasion and migration, and by inducing apoptosis.

Recent insights into the pathophysiology of omental metastases

Although, useful in inflammatory conditions, the greater omentum represents an important site of metastasis in peritoneal carcinomatosis and is therefore frequently removed as a staging or therapeutic tool. Apart from the milky spots, omental adipose stem cells, and adipocytes have recently been identified to play a role in the preferential homing of tumor cells to the omentum. The extent of omentectomy and whether a routine omentectomy should be done are still known unknowns.

A comparison of total versus partial omentectomy for advanced gastric cancer in laparoscopic gastrectomy

Background

Minimally invasive surgery has been slowly introduced into the field of advanced gastric cancer (AGC) surgery. However, the appropriate extent of omentectomy during laparoscopic gastrectomy for AGC is unknown.

Methods

From July 2004 to December 2011, 146 patients with serosa-negative advanced gastric cancer were divided into the total omentectomy group (TO group, n = 80) and the partial omentectomy group (PO group, n = 66). The clinicopathologic characteristics, surgical outcomes, recurrence pattern and survival were analyzed.

Results

There were no significant differences in the clinicopathologic features between the two groups, except for depth of invasion; more T3 (subserosal invasion) cases (65%) were included in total omentectomy group (P = 0.011). The mean time for PO was significantly shorter (35.1 ± 13.0 min) than TO (50.9 ± 15.3 min) (P %0.001), and there were two omentectomy-related complications in the TO group: spleen and mesocolon injuries. Recurrence occurred in 14 (17.5%) and 5 (7.6%) cases in the TO and PO group, respectively (P = 0.054). Disease-free survival (TO versus PO: 81.5% versus 89.3%, P = 0.420) and disease-specific survival (TO versus PO: 89% versus 94.7%) were not significantly different between the two groups. In the case-matched analysis using propensity score matching, there was no difference in disease-free survival (TO versus PO: 83.3% versus 90.5%, P = 0.442).

Conclusions

Partial omentectomy might be an oncologically safe procedure during laparoscopic gastrectomy for serosa-negative advanced gastric cancer, similar to early gastric cancer.

The mannose-sensitive hemagglutination pilus strain of Pseudomonas aeruginosa shift peritoneal milky spot macrophages towards an M1 phenotype to dampen peritoneal dissemination

Peritoneal dissemination (PD) of tumor cells is the most frequent pattern of gastric cancer recurrence and the leading cause of death. Peritoneal milky spots are deemed as the site of origin of gastric cancer PD wherein the main cellular components are macrophages. A vaccine derived from the mannose-sensitive hemagglutination pilus strain of Pseudomonas aeruginosa (PA-MSHA) has exhibit strong immune modulatory properties. In the present study, we tested the hypothesis whether the PA-MSHA vaccine activated peritoneal milky spot macrophages (PMSM) in a manner that would attenuate PD. It was observed that PA-MSHA activated PMSM towards a classical activation phenotype via a toll-like receptor4/9-dependent mechanism, which increased interleukin-12 levels and promoted the expression of co-stimulatory and antigen-presenting molecules like CD80, CD86, and MHC-II (P < 0.05). In addition, PA-MSHA-treated PMSM exhibited strong nonspecific antitumor effects in both contact-dependent and contact-independent modes of action (P < 0.05). In mice treated with PA-MSHA before inoculating gastric cancer cells, we noted alleviated PD toward the untreated mice. In conclusion, our findings demonstrated that PA-MSHA can stimulate PMSM towards an M1 phenotype and that activated PMSM inhibit gastric cancer growth and PD both in vitro and in vivo. The results of the current study provide a mechanistic insight that is relevant to the potential application of PA-MSHA in the treatment of gastric cancer-mediated PD.

Milky spot macrophages remodeled by gastric cancer cells promote peritoneal mesothelial cell injury

Peritoneal dissemination (PD) is the most frequent metastatic pattern of advanced gastric cancer (GC) and the main cause of death in GC patients. Human peritoneal mesothelial cell (HPMC) injury induced by gastric cancer cells (GCCs) and GCC outgrowths supported by peritoneal milky spot macrophages (PMSMs) are the key events during gastric cancer peritoneal dissemination (GCPD). In this study, we investigated whether PMSMs remodeled by GCC can induce HPMC injury and create a favorable microenvironment for GCPD. We established a tumor-associated macrophage (TAM) model using in vitro cell coculture. Normal macrophages cocultured with GCCs down-regulated expression of antigen-presenting surface molecules CD80, CD86, and MHC-II, but, notably, they up-regulated expression of phagocytic scavenger receptor CD206, which is similar to the M2 macrophage phenotype. In further experiments, various experimental methods were applied to detect the injurious effect of TAMs on HPMCs in another TAM-HPMC coculture. Our results showed that GCCs can induce HPMC apoptosis by unregulated apoptosis associated with cleaved caspase3, cleaved caspase9, and p21 proteins. HPMC growth ceased, and both early- and late-stage apoptosis were observed. Additionally, GCCs can induce HPMC fibrosis via increased expression of epithelial cell marker E-cadherin and decreased expression of mesenchymal cell marker α-SMA. Our results demonstrate that, in the GCPD process, PMSMs were remodeled by GCCs, resulting in phenotypic and functional transformation. In turn, this transformation induced HPMC injury and provided a favorable microenvironment for GCC anchorage and growth. These results may provide new insight into the mechanisms of GCPD.

Generation of a dual-functioning antitumor immune response in the peritoneal cavity

Tumor cell metastasis to the peritoneal cavity is observed in patients with tumors of peritoneal organs, particularly colon and ovarian tumors. Following release into the peritoneal cavity, tumor cells rapidly attach to the omentum, a tissue consisting of immune aggregates embedded in adipose tissue. Despite their proximity to potential immune effector cells, tumor cells grow aggressively on these immune aggregates. We hypothesized that activation of the immune aggregates would generate a productive antitumor immune response in the peritoneal cavity. We immunized mice i.p. with lethally irradiated cells of the colon adenocarcinoma line Colon38. Immunization resulted in temporary enlargement of immune aggregates, and after challenge with viable Colon38 cells, we did not detect tumor growth on the omentum. When Colon38-immunized mice were challenged with cells from the unrelated breast adenocarcinoma line E0771 or the melanoma line B16, these tumors also did not grow. The nonspecific response was long-lived and not present systemically, highlighting the uniqueness of the peritoneal cavity. Cellular depletions of immune subsets revealed that NK1.1(+) cells were essential in preventing growth of unrelated tumors, whereas NK1.1(+) cells and T cells were essential in preventing Colon38 tumor growth. Collectively, these data demonstrate that the peritoneal cavity has a unique environment capable of eliciting potent specific and nonspecific antitumor immune responses.

Cancer stem cells: the 'heartbeat' of gastric cancer

Gastric cancer (GC) remains one of the most common cancers worldwide. Its prevalence is still on the rise in the developing countries due to the ageing population. The cancer stem cell (CSC) theory provides a new insight into the interpretation of tumor initiation, aggressive growth, recurrence, and metastasis of cancer, as well as the development of new strategies for cancer treatment. This review will focus on the progress of biomarkers and signaling pathways of CSCs, the complex crosstalk networks between the microenvironment and CSCs, and the development of therapeutic approaches against CSCs, predominantly focusing on GC.

Cell-cell and cell-matrix dynamics in intraperitoneal cancer metastasis

The peritoneal metastatic route of cancer dissemination is shared by cancers of the ovary and gastrointestinal tract. Once initiated, peritoneal metastasis typically proceeds rapidly in a feed-forward manner. Several factors contribute to this efficient progression. In peritoneal metastasis, cancer cells exfoliate into the peritoneal fluid and spread locally, transported by peritoneal fluid. Inflammatory cytokines released by tumor and immune cells compromise the protective, anti-adhesive mesothelial cell layer that lines the peritoneal cavity, exposing the underlying extracellular matrix to which cancer cells readily attach. The peritoneum is further rendered receptive to metastatic implantation and growth by myofibroblastic cell behaviors also stimulated by inflammatory cytokines. Individual cancer cells suspended in peritoneal fluid can aggregate to form multicellular spheroids. This cellular arrangement imparts resistance to anoikis, apoptosis, and chemotherapeutics. Emerging evidence indicates that compact spheroid formation is preferentially accomplished by cancer cells with high invasive capacity and contractile behaviors. This review focuses on the pathological alterations to the peritoneum and the properties of cancer cells that in combination drive peritoneal metastasis.