Getting rid of "H. pylori" in those who are infected decreases the risk of stomach cancer, at least in those who are Asian. A 2014 meta-analysis of observational studies found that a diet high in fruits, mushrooms, garlic, soybeans, and green onions was associated with a lower risk of stomach cancer in the Korean population. Low doses of vitamins, especially from a healthy diet, decrease the risk of stomach cancer. A previous review of antioxidant supplementation did not find supporting evidence and possibly worse outcomes.

The stomach is a muscular organ of the gastrointestinal tract that holds food and begins the digestive process by secreting gastric juice. The most common cancers of the stomach are adenocarcinomas but other histological types have been reported. Signs vary but may include vomiting (especially if blood is present), weight loss, anemia, and lack of appetite. Bowel movements may be dark and tarry in nature. In order to determine whether cancer is present in the stomach, special X-rays and/or abdominal ultrasound may be performed. Gastroscopy, a test using an instrument called endoscope to examine the stomach, is a useful diagnostic tool that can also take samples of the suspected mass for histopathological analysis to confirm or rule out cancer. The most definitive method of cancer diagnosis is through open surgical biopsy. Most stomach tumors are malignant with evidence of spread to lymph nodes or liver, making treatment difficult. Except for lymphoma, surgery is the most frequent treatment option for stomach cancers but it is associated with significant risks.

Cancer of the stomach, also called gastric cancer, is the fourth-most-common type of cancer and the second-highest cause of cancer death globally. Eastern Asia (China, Japan, Korea, Mongolia) is a high-risk area for gastric cancer, and North America, Australia, New Zealand and western and northern Africa are areas with low risk. The most common type of gastric cancer is adenocarcinoma, which causes about 750,000 deaths each year. Important factors that may contribute to the development of gastric cancer include diet, smoking and alcohol consumption, genetic aspects (including a number of heritable syndromes) and infections (for example, "Helicobacter pylori" or Epstein-Barr virus) and pernicious anemia. Chemotherapy improves survival compared to best supportive care, however the optimal regimen is unclear.

Digestive system neoplasms are tumors which affect the digestive system. Types include:

- esophageal cancer

- gastric cancer

- small intestinal cancer

- colorectal cancer

- anal cancer

Pancreatic cancer is the fifth-most-common cause of cancer deaths in the United States, and the seventh most common in Europe. In 2008, globally there were 280,000 new cases of pancreatic cancer reported and 265,000 deaths. These cancers are classified as endocrine or nonendocrine tumors. The most common is ductal adenocarcinoma. The most significant risk factors for pancreatic cancer are advanced age (over 60) and smoking. Chronic pancreatitis, diabetes or other conditions may also be involved in their development. Early pancreatic cancer does not tend to result in any symptom, but when a tumor is advanced, a patient may experience severe pain in the upper abdomen, possibly radiating to the back. Another symptom might be jaundice, a yellowing of the skin and eyes.

Pancreatic cancer has a poor prognosis, with a five-year survival rate of less than 5%. By the time the cancer is diagnosed, it is usually at an advanced, inoperable stage. Only one in about fifteen to twenty patients is curative surgery attempted. Pancreatic cancer tends to be aggressive, and it resists radiotherapy and chemotherapy.

Surgical treatment remains the treatment of choice for cats and dogs diagnosed with intestinal tumors who are in otherwise good health.

Chemotherapy has relatively poor curative efficacy in SRCC patients and overall survival rates are lower compared to patients with more typical cancer pathology. SRCC cancers are usually diagnosed during the late stages of the disease, so the tumors generally spread more aggressively than non-signet cancers, making treatment challenging. In the future, case studies indicate that bone marrow metastases will likely play a larger role in the diagnosis and management of signet ring cell gastric cancer.

In SRCC of the stomach, removal of the stomach cancer is the treatment of choice. There is no combination of chemotherapy which is clearly superior to others, but most active regimens include 5-Fluorouracil (5-FU), Cisplatin, and/or Etoposide. Some newer agents, including Taxol and Gemcitabine (Gemzar) are under investigation.

In a single case study of a patient with SRCC of the bladder with recurrent metastases, the patient exhibited a treatment response to palliative FOLFOX-6 chemotherapy.

The median age at diagnosis is 38 years. Women are at higher risk for developing breast cancer.

Since Krukenberg tumors are secondary (metastatic), management might logically be driven by identifying and treating the primary cancer. The optimal treatment of Krukenberg tumors is unclear. The role of surgical resection has not been adequately addressed but if metastasis is limited to the ovaries, surgery may improve survival. The role of chemotherapy and/or radiotherapy is uncertain but may sometimes be beneficial.

Primary gastric lymphoma (lymphoma that originates in the stomach itself) is an uncommon condition, accounting for less than 15% of gastric malignancies and about 2% of all lymphomas. However, the stomach is a very common extranodal site for lymphomas (lymphomas originating somewhere else with metastasis to stomach). It is also the most common source of lymphomas in the gastrointestinal tract.

Primary signet-ring cell carcinoma of the urinary bladder is extremely rare and patient survival is very poor and occurs mainly in men ages 38 to 83. However, one such patient treated with a radical cystectomy followed by combined S-1 and Cisplatin adjuvant chemotherapy did demonstrate promising long-term survival of 90 months.

Surgical removal of the stomach (gastrectomy) is typically recommended after for people after 20 years of age, and before 40 years of age.

Smoking has been linked to a variety of disorders of the stomach. Tobacco is known to stimulate acid production and impairs production of the protective mucus. This leads to development of ulcers in the majority of smokers.

Chronic stomach problems have also been linked to excess intake of alcohol. It has been shown that alcohol intake can cause stomach ulcer, gastritis and even stomach cancer. Thus, avoidance of smoking and excess alcohol consumption can help prevent the majority of chronic stomach disorders.

One of the most causes of chronic stomach problems is use of medications. Use of aspirin and other non-steroidal anti-inflammatory drugs to treat various pain disorders can damage lining of the stomach and cause ulcers. Other medications like narcotics can interfere with stomach emptying and cause bloating, nausea, or vomiting.

The majority of chronic stomach problems are treated medically. However, there is evidence that a change in life style may help. Even though there is no specific food responsible for causing chronic stomach problems, experts recommend eating a healthy diet which consists of fruits and vegetables. Lean meat should be limited. Moreover, people should keep a diary of foods that cause problems and avoid them.

Most people affected by primary gastric lymphoma are over 60 years old. Symptoms include epigastric pain, early satiety, fatigue and weight loss.

Proton pump inhibitors (such as omeprazole and lansoprazole) and histamine H2-receptor antagonists (such as famotidine and ranitidine) are used to slow acid secretion. Once gastric acid is suppressed, symptoms normally improve.

A Krukenberg tumor refers to a malignancy in the ovary that metastasized from a primary site, classically the gastrointestinal tract, although it can arise in other tissues such as the breast. Gastric adenocarcinoma, especially at the pylorus, is the most common source. Krukenberg tumors are often (over 80%) found in both ovaries, consistent with its metastatic nature.

Surgery, with as wide a margin of removal as possible, has generally been the most effective and preferred way to attack LMS. If surgical margins are narrow or not clear of tumor, however, or in some situations where tumor cells were left behind, chemotherapy or radiation has been shown to give a clear survival benefit. While LMS tends to be resistant to radiation and chemotherapy, each case is different and results can vary widely.

LMS of uterine origin do frequently, but not always respond to hormonal treatments.

The average age at which intestinal tumors are diagnosed ranges between 10–12 years for cats and 6 to 9 years for dogs. There are many different types of intestinal tumors, including lymphoma, adenocarcinoma, mast cell tumor, and leiomyosarcoma.

There is a risk of development of cancer with fundic gland polyposis, but it varies based on the underlying cause of the polyposis. The risk is highest with congenital polyposis syndromes, and is lowest in acquired causes. As a result, it is recommended that patients with multiple fundic polyps have a colonoscopy to evaluate the colon. If there are polyps seen on colonoscopy, genetic testing and testing of family members is recommended.

In the gastric adenocarcinoma associated with proximal polyposis of the stomach (GAPPS), there is a high risk of early development of proximal gastric adenocarcinoma.

It is still unclear which patients would benefit with surveillance gastroscopy, but most physicians recommend endoscopy every one to three years to survey polyps for dysplasia or cancer. In the event of high grade dysplasia, polypectomy, which is done through the endoscopy, or partial gastrectomy may be recommended. One study showed the benefit of NSAID therapy in regression of gastric polyps, but the efficacy of this strategy (given the side effects of NSAIDs) is still dubious.

Fundic gland polyposis is a medical syndrome where the fundus and the body of the stomach develop many polyps. The condition has been described both in patients with familial adenomatous polyposis (FAP) and attenuated variants (AFAP), and in patients in whom it occurs sporadically.

Cetuximab is the first-line therapy for Ménétrier disease. Cetuximab is a monoclonal antibody against epidermal growth factor receptor (EGFR), and has been shown to be effective in treating Ménétrier disease.

Several medications have been used in the treatment of the condition, with variable efficacy. Such medications include: anticholinergic agents, prostaglandins, proton pump inhibitors, prednisone, and H2 receptor antagonists. Anticholinergics decrease protein loss. A high-protein diet should be recommended to replace protein loss in patients with low levels of albumin in the blood (hypoalbuminemia). Any ulcers discovered during the evaluation should be treated in standard fashion.

Severe disease with persistent and substantial protein loss despite cetuximab may require total removal of the stomach. Subtotal gastrectomy is performed by some; it may be associated with higher morbidity and mortality secondary to the difficulty in obtaining a patent and long-lasting anastomosis between normal and hyperplastic tissue. In adults, there is no FDA approved treatment other than gastrectomy and a high-protein diet. Cetuximab is approved for compassionate use in the treatment of the disease.

Pediatric cases are normally treated for symptoms with the disease clearing up in weeks to months.

Uterine sarcoma are rare, out of all malignancies of the uterine body only about 4% will be uterine sarcomas. Generally, the cause of the lesion is not known, however patients with a history of pelvic radiation are at higher risk. Most tumors occur after menopause.

Women who take long-term tamoxifen are at higher risk.

Therapy is based on staging and patient condition and utilizes one or more of the following approaches.

Surgery is the mainstay of therapy if feasible involving total abdominal hysterectomy with bilateral salpingo-oophorectomy. Other approaches include radiation therapy, chemotherapy, and hormonal therapy.

Prognosis is relatively poor.

The average age of onset is 40 to 60 years, and men are affected more often than women. Adults with Ménétrier disease have a higher risk of developing gastric adenocarcinoma.

There are many tools for investigating stomach problems. The most common is endoscopy. This procedure is performed as an outpatient and utilizes a small flexible camera. The procedure does require intravenous sedation and takes about 30–45 minutes; the endoscope is inserted via the mouth and can visualize the entire swallowing tube, stomach and duodenum. The procedure also allows the physician to obtain biopsy samples. In many cases of bleeding, the surgeon can use the endoscope to treat the source of bleeding with laser, clips or other injectable drugs.