This is a pilot study aiming at evaluating the effects of PIPAC with Doxorubicin + Cisplastin on patients with PM of gastric cancer. All patients who are diagnosed with gastric cancer with peritoneal metastases in the Prince of Wales Hospital (PWH), HK will be screened for eligibility.

There are two aims for this study:

1. To evaluate safety and efficacy of the procedure together with postoperative outcomes and long term overall and progression free survival.
2. Aim at obtaining tissue samples for molecular analysis and for potential tissue organoids and biobank.

The current study aims to establish the safety, feasibility of PIPAC in gastric cancer with peritoneal metastases. Furthermore, if this multimodal therapy is established, different chemotherapy or combination with immunotherapy can be used to achieve optimal therapeutic effect.

The investigators aim to recruit 30 patients or until 5 years has been reached. The patients will then be followed-up to up to 5 years or death. A first report regarding the safety and feasibility would be generated after 15 patients complete the 6-month follow-up.

Clinical Outcomes:

Data of all patients who underwent PIPAC procedure will be included in a prospectively maintained database. Safety, tolerability, and postoperative complications will be assessed by collection of adverse events, according to the Common Terminology Criteria for Adverse Events (CTCAE) v6.0 including physical examination results and laboratory assessments (chemistry and hematology). PCI, Karnofsky index, peritoneal regression grading score (PRGS), time point of peritoneal metastasis (synchronous vs. metachronous), number of previous chemotherapy lines, and presence of ascites will be recorded. Computed tomography (CT) will be performed as restaging. Patients' overall survival, progression free survival will also be recorded.

DNA Extraction and Bisulfite Modification:

DNA from each plasma sample will be extracted using QIAamp DNA Blood Mini Kit (Qiagen, Valencia, CA). Sodium bisulfite modification, which converts unmethylated CpG sites to UpG without affecting methylated sites, will be achieved using Zymo DNA Modification Kit (Zymo Research, Orange, CA).

Detection of Methylated Target DNA Using Digital PCR:

Conventional quantitative PCR (qPCR) suffers from a number of technical limitations including a relatively low sensitivity level of 0.5 to 1%. In order to differentiate methylated tumour cellfree DNA from a high background of unmethylated DNA in plasma samples, digital PCR, which enables detection and quantitation of target DNA at sensitivity level of 0.001%, will be adopted to achieve highly sensitive and specific detection. Digital PCR is a new approach to nucleic acid detection and quantification that offers an alternate method to conventional real-time quantitative PCR for absolute quantification (no need to rely on references or standards) and rare allele detection.

Digital PCR works by partitioning a sample of DNA or cDNA into many individual, parallel PCR reactions such that there is either zero or one target molecule present in any individual reaction. Thermal cycling is then performed to endpoint. A single molecule can be amplified a million-fold or more. Any target-containing compartments will become brightly fluorescent while compartments without targets will have only background fluorescence. In fact, digital PCR has been widely adoptednas an innovative approach for detecting copy number variations and rare mutations in patients' body fluids.

RainDrop digital PCR system (RainDance Technologies, Billerica, MA) will be used to detect methylated target DNA. Bisulfite-modified DNA (template) will first be mixed with TaqMan Genotyping Master Mix (Life Technologies, Carlsbad, CA), 10X Drop Stabiliser (RainDance Technologies), 0.5uM each of forward and reverse primers, 0.2uM TaqMan MGB probe (Life Technologies) and water in a total volume of 50uL. Distinct primers and probes will be designed for each of the five target genes using MethPrimer.

The PCR reaction mix will then be converted into millions of micro-droplets approximately 5pL in volume by RainDrop Source followed by thermal cycling at 95°C for 10 minutes, 45 cycles of 95°C for 15 sceonds and 60°C for 1 minute, 98°C for 10 minutes using Veriti Thermal Cycler (Applied Biosystems, Foster City, CA). The thermalcycled droplets will be loaded onto the RainDrop Sense where the instrument reads the fluorescent intensity of each droplet. Positive and negative droplets for each target gene will be analyzed using the RainDrop Analyst software.

Pre-therapeutic Workup:

Patients eligibility for the study will be screened at the upper gastrointestinal cancer clinic (UGIC), PWH, HK. A written consent will be obtained from the patient.

The following assessments will be performed:

(i) Performance status evaluation, (ii) Esophagogastroduodenoscopy (EGD) (iii) Endoscopic ultrasound (EUS) (optional) (iv) CT thorax + abdomen + pel + IV contrast (v) Laboratory exams: serum complete blood count, liver, renal function tests, glucose, CEA, clotting profile, CrCl (vi) Electrocardiogram (ECG) (vii) Creatinine Clearance (viii) QoL assessment (QLQ-C30) (ix) Dietician consultation (x) Oncologist consultation

The case will be discussed in the tumor board meeting (TBM) for eligibility of the study. The flow of the treatment will follow the flowchart. Patients will receive standard mono-or poly-chemotherapy proposed by the oncologist such as XELOX, FLOT, monotherapy S1, or any new guideline-approved standard validated during the study, until progression or toxicity. Patients can be included regardless of the number of lines of chemotherapy received. However, no systemic chemotherapy is allowed 2 weeks before and 1 week after PIPAC; and PIPAC can only be performed at a minimum of 6 week intervals.

Surgical Technique Explorative laparoscopy: PCI is determined according to Sugarbaker, based on lesion size and distribution. Using a pictorial of the abdomen, each location of a 13 point list (central abdominal wall, right upper abdominal wall, epigastrium, left upper abdominal wall, left flank, left lower quadrant, pelvis, right lower quadrant, right flank, upper jejunum, lower jejunum, upper ileum, lower ileum) received a PCI grade ranging from 0 to 3, i.e. no visible carcinomatosis, isolated tumor cells, multiple tumor nodules, and confluent lesions. The sum of all 13 grades was noted as PCI. Biopsy will be taken at the sites with positive or suspected peritoneal nodules for histological confirmation. The procedure will also be recorded.

In case of PCI score <=8, and patient is fit and agrees to proceed to CRS + HIPEC, patient will not be included in the study.

In case of PCI score >8, patient will be included in this study.

Pressurized intraperitoneal aerosolised chemotherapy (PIPAC): After insufflation of a 12mmHg of capnoperitoneum at 37oC, two balloons safety trocars (10 and 12mm) are inserted into the abdominal cavity. A biopsy is taken for pathologic confirmation of PC during the first procedure and all following procedures in order to ascertain tumor regression grade. Biopsy will be taken at the previous site of positive histology according to previous videos and also on new lesions. Ascites volume is documented and ascites is suctioned out. Then a nebulizer CAPNOPEN (Reger Medizintechnik, GmbH, Villingendorf, Germany) is connected to an intravenous high-pressure injector and inserted into the abdomen. The tightness of the abdomen is confirmed via a zero-flow of CO2. Injection parameters are set at a flow rate of 30ml/min and a maximum upstream pressure of 200 psi in the high-pressure injector. The injection is remote-controlled to minimize personnel exposure. The safety protocol with checklist containing all safety aspects as described previously was systemically double-checked before administration of cytostatics.

After application of doxorubicin (2.1mg/m2 in 50ml NaCl 0.9%) and cisplatin (10.5mg/m2 body surface in 150ml NaCl 0.9%), the therapeutic capnoperitoenaum is maintained for 30min at a temperature of 37oC. Then, the chemotherapy aerosol is exhausted over a closed surgical smoke extractor. Finally, trocars are retracted and laparoscopy ended. No drain is inserted to the abdominal cavity. The study aims to perform PIPAC 3 times, once every 6-8 weeks. A median 2.5 PIPAC procedures of per patient is expected because of the possibility of adhesions preventing access to the abdomen.

Tissue Sampling:

1. Molecular analysis

1. A section of the peritoneal nodule taken during laparoscopy will be collected. Oesophagogastroduodenoscopy (OGD) will also be performed during general anesthesia for gastric tumor biopsy. Four 12ml of peripheral blood, one before PIPAC and three after each PIPAC, will be obtained from each participant. Plasma samples will be isolated by centrifugation. Plasma and tissue samples will be stored at -80 degree Celsius until further analysis.
2. Timepoints:

i. Baseline (during first laparoscopy for #1 PIPAC) ii. During laparoscopy for #2 PIPAC iii. During laparoscopy for #3 PIPAC iv. In case further laparoscopy is performed for restaging after completion of all chemotherapy

Laparoscopy for Final Evaluation:

Depending on patient's condition and disease responsiveness upon completion of chemotherapy, a staging laparoscopy may be performed at 3 months (e.g.: 1 month after the third PIPAC application) to reassess operability of the tumor. PCI and ascites volume will be documented, and tumor biopsy will be taken in order to ascertain tumor regression. Ascites volume will be documented and then removed. Decision to perform this last laparoscopy will be made in accordance to the referring physician, surgeon or oncologist.

In case of PCI major decrease <= 8 after the PIPAC procedures or after intravenous chemotherapy, extended biopsy will be performed. The tumor response confirmed by pathological analysis according to previous published guidelines for post PIPAC analysis. If confirmed a proposition to perform a cytoreductive surgery, including HIPEC is discussed with the patient and in the tumor board meeting.

Follow-up:

After PIPAC, patients will remain as inpatient for 2 days. They will be evaluated with clinical examination daily. For the first post-operative day, laboratory exams will be performed in order to assess haematological, renal and hepatic functions. Locoregional toxicity and systemic toxicity will be evaluated according to the Common Terminology Criteria for Adverse Events (CTC-AR v6.0) from the National Cancer Institute of the United States Department of Health & Human Services.

Patients will also be reviewed for fitness to receive systemic chemotherapy post-operatively as per their usual care. The patients will be seen postoperatively 2 weeks after each PIPAC, then every 3 months till patient succumbs. During each visit, patients will undergo a clinical examination, an evaluation of the QoL (using QLQ C30), an assessment of tolerance (CTCAE V6), routine laboratory test including complete blood count, renal and liver function tests, an assay for tumor biomarkers (CEA).

A follow up CT scan of the chest and abdomen will be performed as clinically indicated. If patient deemed not fit to proceed to further PIPAC or patient refuse, then no further PIPAC will be proceeded. For all patients, clinical follow-up with all events and endpoints will be collected and analysed within 5 years from their inclusion. Beginning with the start of PIPAC, any new event/ experience that was not present at baseline, or worsening of an event present at baseline, is considered an adverse event. If the event meets the criteria of serious adverse event, it will be recorded within the 30-day after each PIPAC.

This study contribute in evaluating the safety and efficacy of the procedure together with postoperative outcomes and long term overall and progression free survival.

Inclusion Criteria:

1. Patients age >= 18, <= 80 years old
2. Performance status (WHO) <=2
3. Histologically evidenced synchronous PM of gastric adenocarcinoma cancer
4. Peritoneal Cancer Index (PCI) score > 8, or <=8 and patient not fit for cytoreductive surgery + hyperthermic intraperitoneal chemotherapy (CRS + HIPEC)
5. Patients with isolated ovarian metastasis could be included
6. White blood cells >3.5000/mm3; neutrophils > 1.500/mm3; platelets >100,000/mm3
7. Creatinine <1.5mg/dL and creatinine clearance >60ml/min and serum total bilirubin <2mg/dL
8. Ability to give written consent prior to commencement of treatment

Exclusion Criteria:

1. Extraperitoneal metastases including liver metastases and malignant pleural effusion. The presence of suspicious retroperitoneal lymph nodes is not an exclusion criterium.
2. Patients with adenocarcinoma of Siewart I
3. Bowel obstruction, not tolerating oral diet
4. HER2+++ tumor with indicated for Trastuzumab therapy
5. Any laparotomy during 3 months before inclusion. (Laparoscopy is not an exclusion criterium)
6. Contraindicated to any drug contained in the chemotherapy regimen
7. Concomitant intraperitoneal chemotherapy, immunotherapy or target therapy
8. Active infectious (bacterial, viral) disease. Elevated CRP with no identified focus is not an exclusion criterium
9. Pregnancy or breastfeeding