Diet and lifestyle are believed to play a large role in whether colorectal polyps form. Studies show there to be a protective link between consumption of cooked green vegetables, brown rice, legumes, and dried fruit and decreased incidence of colorectal polyps.

Little research is conducted on these cancers due to their relative rarity when compared to the more common colorectal cancers. APC-min mice which carry a gene deficiency corresponding to that of humans with FAP also go on to develop small intestinal tumors, though humans do not.

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.

People with Barrett's esophagus (a change in the cells lining the lower esophagus) are at much higher risk, and may receive regular endoscopic screening for the early signs of cancer. Because the benefit of screening for adenocarcinoma in people without symptoms is unclear, it is not recommended in the United States. Some areas of the world with high rates of squamous-carcinoma have screening programs.

Prevention includes stopping smoking or chewing tobacco. Overcoming addiction to areca chewing in Asia is another promising strategy for the prevention of esophageal squamous-cell carcinoma. The risk can also be reduced by maintaining a normal body weight.

According to the National Cancer Institute, "diets high in cruciferous (cabbage, broccoli/broccolini, cauliflower, Brussels sprouts) and green and yellow vegetables and fruits are associated with a decreased risk of esophageal cancer." Dietary fiber is thought to be protective, especially against esophageal adenocarcinoma. There is no evidence that vitamin supplements change the risk.

The median overall survival rate is about 50% in 5 years. Worse prognostic factors include the presence of residual tumor at the margin of the resection specimen (R+), invasion of the peritoneum and metastatic disease.

Risk factors for small intestine cancer include:

- Crohn's disease

- Celiac disease

- Radiation exposure

- Hereditary gastrointestinal cancer syndromes: familial adenomatous polyposis, hereditary nonpolyposis colorectal cancer, Peutz-Jeghers syndrome

- Males are 25% more likely to develop the disease

Benign tumours and conditions that may be mistaken for cancer of the small bowel:

- Hamartoma

- Tuberculosis

Surgery is the mainstay of treatment for clinically localized disease. In feasible cases, a partial cystectomy with "en-bloc" resection of the median umbilical ligament and umbilicus can achieve good results. In progressed stages, radiotherapy seems not to lead to sufficient response rates. However, chemotherapy regimes containing 5-FU (and Cisplatin) have been described to be useful in these cases. In recent years, targeted therapies have been demonstrated to be useful in reports of single cases. These agents included Sunitinib, Gefitinib, Bevacizumab and Cetuximab.

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.

Oesophagogastric junctional adenocarcinoma is a cancer of the lower part of the oesophagus, often linked to a Barrett's oesophagus.

The incidence of oesophagogastric junctional adenocarcinoma is rising rapidly in western countries, in contrast to the declining frequency of distal gastric adenocarcinoma. Treatment options for adenocarcinomas involving the oesophagogastric junction are limited and the overall prognosis is extremely poor.

Treatment is variable, both due to its rarity and to its frequently slow-growing nature. Treatment ranges from watchful waiting to debulking and hyperthermic intraperitoneal chemotherapy (HIPEC, also called intraperitoneal hyperthermic chemotherapy, IPHC) with cytoreductive surgery.

Surgery remains the front-line therapy for HNPCC. There is an ongoing controversy over the benefit of 5-fluorouracil-based adjuvant therapies for HNPCC-related colorectal tumours, particularly those in stages I and II.

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.

Resection is sometimes a part of a treatment plan, but duodenal cancer is difficult to remove surgically because of the area that it resides in—there are many blood vessels supplying the lower body. Chemotherapy is sometimes used to try to shrink the cancerous mass. Other times intestinal bypass surgery is tried to reroute the stomach to intestine connection around the blockage.

A 'Whipple' procedure is a type of surgery that is sometimes possible with this cancer. In this procedure, the duodenum, a portion of the Pancreas (the head), and the gall bladder are usually removed, the small intestine is brought up to the Pylorus (the valve at the bottom of the stomach) and the Liver and Pancreas digestive enzymes and bile are connected to the small intestine below the Pylorus.

The removal of part of the Pancreas often requires taking Pancreatic Enzyme supplements to aid digestion. These are available in the form of capsules by prescription.

It is not unusual for a patient having received a Whipple procedure to feel perfectly well, and to lead his/her normal life without difficulty.

It is important for the procedure to be performed by a surgeon with extensive experience having done and observed the procedure, as specific competence makes a big difference.

Some patients need to be fitted with tubes to either add nutrients (feeding tubes) or drainage tubes to remove excess processed food that can not pass the blockage.

Polyps can be removed during a colonoscopy or sigmoidoscopy using a wire loop that cuts the stalk of the polyp and cauterises it to prevent bleeding. Many "defiant" polyps—large, flat, and otherwise laterally spreading adenomas—may be removed endoscopically by a technique called endoscopic mucosal resection (EMR), which involves injection of fluid underneath the lesion to lift it and thus facilitate surgical excision. These techniques may be employed as an alternative to the more invasive colectomy.

The cancerous mass tends to block food from getting to the small intestine. If food cannot get to the intestines, it will cause pain, acid reflux, and weight loss because the food cannot get to where it is supposed to be processed and absorbed by the body.

Patients with duodenal cancer may experience abdominal pain, weight loss, nausea, vomiting, and chronic GI bleeding.

Barrett's esophagus is a premalignant condition. Its malignant sequela, oesophagogastric junctional adenocarcinoma, has a mortality rate of over 85%. The risk of developing esophageal adenocarcinoma in people who have Barrett's esophagus has been estimated to be 6–7 per 1000 person-years, however a cohort study of 11,028 patients from Denmark published in 2011 showed an incidence of only 1.2 per 1000 person-years (5.1 per 1000 person-years in patients with dysplasia, 1.0 per 1000 person-years in patients without dysplasia). The relative risk of esophageal adenocarcinoma is approximately 10 in those with Barret's esophagus, compared to the general population. Most patients with esophageal carcinoma survive less than one year.

The standard of care for mucinous adenocarcinoma with clinical condition PMP involves cytoreductive surgery (CRS) with hyperthermic intraperitoneal chemotherapy (HIPEC), by surgical oncologists who specialize in treating PMP. Some surgeons also apply early post-operative intraperitonial chemotherapy (EPIC), adjunct to surgical cytoreduction and HIPEC. In situations where surgery is not required immediately, patients can be monitored via CT scans, tumor marker laboratory tests, and physical symptoms, to determine when, and if, surgery is warranted. Although some surgical procedures may be rather extensive, patients can and do recover from surgery, and the majority of these patients can and do live productive lives.

In debulking, the surgeon attempts to remove as much tumor as possible. CRS or cytoreductive surgery involves surgical removal of the peritoneum and any adjacent organs which appear to have tumor seeding. Since the mucus tends to pool at the bottom of the abdominal cavity, it is common to remove the ovaries, fallopian tubes, uterus, and parts of the large intestine. Depending upon the spread of the tumor, other organs might be removed, including but not limited to the gallbladder, spleen, and portions of the small intestine and/or stomach. For organs that cannot be removed safely (like the liver), the surgeon strips off the tumor from the surface.

Many people with Barrett's esophagus do not have dysplasia. Medical societies recommend that if a patient has Barrett's esophagus, and if the past two endoscopy and biopsy examinations have confirmed the absence of dysplasia, then the patient should not have another endoscopy within three years.

Endoscopic surveillance of people with Barrett's esophagus is often recommended, although little direct evidence supports this practice. Treatment options for high-grade dysplasia include surgical removal of the esophagus (esophagectomy) or endoscopic treatments such as endoscopic mucosal resection or ablation (destruction).

The risk of malignancy is highest in the U.S. in Caucasian men over fifty years of age with more than five years of symptoms. Current recommendations include routine endoscopy and biopsy (looking for dysplastic changes). Although in the past physicians have taken a watchful waiting approach, newly published research supports consideration of intervention for Barrett's esophagus. Balloon-based radiofrequency ablation, invented by Ganz, Stern, and Zelickson in 1999, is a new treatment modality for the treatment of Barrett's esophagus and dysplasia, and has been the subject of numerous published clinical trials. The findings demonstrate radiofrequency ablation has an efficacy of 90% or greater with respect to complete clearance of Barrett's esophagus and dysplasia with durability up to five years and a favorable safety profile.

Proton pump inhibitor drugs have not been proven to prevent esophageal cancer. Laser treatment is used in severe dysplasia, while overt malignancy may require surgery, radiation therapy, or systemic chemotherapy. Additionally, a recent five-year random-controlled trial has shown that photodynamic therapy using photofrin is statistically more effective in eliminating dysplastic growth areas than sole use of a proton pump inhibitor. There is presently no reliable way to determine which patients with Barrett esophagus will go on to develop esophageal cancer, although a recent study found the detection of three different genetic abnormalities was associated with as much as a 79% chance of developing cancer in six years.

Endoscopic mucosal resection has also been evaluated as a management technique. Additionally an operation known as a Nissen fundoplication can reduce the reflux of acid from the stomach into the esophagus.

In a variety of studies, nonsteroidal anti-inflammatory drugs (NSAIDS), like aspirin, have shown evidence of preventing esophageal cancer in people with Barrett's esophagus. However, none of these studies have been randomized, placebo-controlled trials, which are considered the gold standard for evaluating a medical intervention. In addition, the best dose of NSAIDs for cancer prevention is not yet known.

Gastrointestinal cancer refers to malignant conditions of the gastrointestinal tract (GI tract) and accessory organs of digestion, including the esophagus, stomach, biliary system, pancreas, small intestine, large intestine, rectum and anus. The symptoms relate to the organ affected and can include obstruction (leading to difficulty swallowing or defecating), abnormal bleeding or other associated problems. The diagnosis often requires endoscopy, followed by biopsy of suspicious tissue. The treatment depends on the location of the tumor, as well as the type of cancer cell and whether it has invaded other tissues or spread elsewhere. These factors also determine the prognosis.

Overall, the GI tract and the accessory organs of digestion (pancreas, liver, gall bladder) are responsible for more cancers and more deaths from cancer than any other system in the body. There is significant geographic variation in the rates of different gastrointestinal cancers.

In the United States, about 160,000 new cases of colorectal cancer are diagnosed each year. Hereditary nonpolyposis colorectal cancer is responsible for approximately 2 percent to 7 percent of all diagnosed cases of colorectal cancer. The average age of diagnosis of cancer in patients with this syndrome is 44 years old, as compared to 64 years old in people without the syndrome.

OGJ adenocarcinoma is a highly mutated and heterogeneous disease. Microsatellite instability (MSI) can be observed and coincides with an elevated number of somatic mutations. Potentially actionable coding mutations have been identified in 67 genes, including those in CR2, HGF, FGFR4 and ESRRB. Numerous genes harbouring somatic coding mutations and copy number changes in the microsatellite stable (MSS) OGJA are also known to be altered with similar predicted functional consequence in other tumour types. TP53, SYNE1, and ARID1A are among the most frequently mutated genes.

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.

Apart from not smoking, the American Cancer Society recommends keeping a healthy weight, and increasing consumption of fruits, vegetables, and whole grains, while decreasing consumption of red and processed meat, although there is no consistent evidence this will prevent or reduce pancreatic cancer specifically. A 2014 review of research concluded that there was evidence that consumption of citrus fruits and curcumin reduced risk of pancreatic cancer, while there was possibly a beneficial effect from whole grains, folate, selenium, and non-fried fish.

In the general population, screening of large groups is not currently considered effective, although newer techniques, and the screening of tightly targeted groups, are being evaluated. Nevertheless, regular screening with endoscopic ultrasound and MRI/CT imaging is recommended for those at high risk from inherited genetics.

Treatment may include the following:

- Surgery with or without radiation

- Radiotherapy

Fast neutron therapy has been used successfully to treat salivary gland tumors, and has shown to be significantly more effective than photons in studies treating unresectable salivary gland tumors.

- Chemotherapy