Intraperitoneal and Intravenous Paclitaxel Chemotherapy With Oral Capecitabine for Gastric Adenocarcinoma With Peritoneal Carcinomatosis

-INCLUSION CRITERIA:

1. Patients must have histologically or cytologically confirmed gastric adenocarcinoma, including Siewert III gastroesophageal junction adenocarcinoma, confirmed by the National Cancer Institute (NCI) Laboratory of Pathology, and have provided a block or unstained slides of primary or

   metastatic tumor tissue or newly obtained fresh biopsy of a tumor lesion in case archival tissue sample is not available.
2. Patients may be treatment naive or have received systemic chemotherapy prior to enrollment:

   * Trastuzumab allowed as prior treatment for human epidermal growth factor receptor 2 (HER2)/neu over-expressing cancers as clinically indicated.
   * Last dose of chemotherapy at least 2 weeks prior to enrollment with recovery to Grade 1 from chemotherapy-related toxicities.
3. Radiographic evidence of peritoneal carcinomatosis and/or sub-radiographic evidence of peritoneal carcinomatosis found at staging laparoscopy.
4. Age \>=18 years. Children under the age of 18 will not participate in this study as gastric cancer is rare in this population.
5. Eastern Cooperative Oncology Group (ECOG) performance status \<=1
6. Patients must have normal organ and marrow function as defined below:

   hemoglobin \>=8.0 g/dL

   absolute neutrophil count \>=1,000/mcL

   platelets \>=100,000/mcL

   total bilirubin \<=1.5 X institutional upper limit of normal

   Aspartate aminotransferase (AST) serum glutamic-oxaloacetic transaminase (SGOT)/alanine aminotransferase (ALT) serum glutamic-pyruvic transaminase (SGPT) \<=2.5 X institutional upper limit of normal

   creatinine \<1.5 mg/dl

   OR

   creatinine clearance \>=60 mL/min/1.73 m\^2 for patients with creatinine levels above institutional normal.
7. Physiologically able to undergo laparoscopy and systemic chemotherapy.
8. Ability of subject to understand and the willingness to sign a written informed consent document.
9. Previous exploratory laparotomy or laparoscopy with tissue biopsy or peritoneal lavage is permitted.
10. Women of child-bearing potential and men must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) prior to study entry and for the duration of study treatment. Should a woman become pregnant or suspect she is pregnant while she or her partner is participating in this study, she should inform her treating physician immediately.
11. Patients must be co-enrolled in protocol 13C0176 (NCT01915225) and 17C0044 (NCT03027427) for sample collection.
12. Human immunodeficiency virus (HIV)-positive patients may be considered for this study only after consultation with a National Institute of Allergy and Infectious Diseases (NIAID) physician.

EXCLUSION CRITERIA:

1. Patients who are receiving any other investigational agents.
2. Previous cytoreductive surgery or intraperitoneal chemotherapy.
3. Disseminated extra-peritoneal or solid organ metastases:

   * Excludes greater omentum and ovarian metastases.
   * Radiographic signs or clinical symptoms consistent with malignant bowel obstruction.
4. History of allergic reactions attributed to compounds of similar chemical or biologic composition to Paclitaxel or Capecitabine or other agents used in study.
5. Previous treatment with paclitaxel or nab-paclitaxel resulting in progression of disease.
6. Existing peripheral neuropathy, Grade 3 or greater.
7. Past medical history of dihydropyrimidine dehydrogenase deficiency.
8. Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements.
9. Pregnant women are excluded because paclitaxel and capecitabine can cause fetal harm when administered to pregnant women. Because there is an unknown but potential risk for adverse events in nursing infants secondary to treatment of the mother with paclitaxel and capecitabine, breastfeeding should be discontinued if the mother is treated with paclitaxel and capecitabine.