Stomach cancer is often either asymptomatic (producing no noticeable symptoms) or it may cause only nonspecific symptoms (symptoms that may also be present in other related or unrelated disorders) in its early stages. By the time symptoms occur, the cancer has often reached an advanced stage (see below) and may have metastasized (spread to other, perhaps distant, parts of the body), which is one of the main reasons for its relatively poor prognosis. Stomach cancer can cause the following signs and symptoms:

Early cancers may be associated with indigestion or a burning sensation (heartburn). However, less than 1 in every 50 people referred for endoscopy due to indigestion has cancer. Abdominal discomfort and loss of appetite, especially for meat, can occur.

Gastric cancers that have enlarged and invaded normal tissue can cause weakness, fatigue, bloating of the stomach after meals, abdominal pain in the upper abdomen, nausea and occasional vomiting, diarrhea or constipation. Further enlargement may cause weight loss or bleeding with vomiting blood or having blood in the stool, the latter apparent as black discolouration (melena) and sometimes leading to anemia. Dysphagia suggests a tumour in the cardia or extension of the gastric tumour into the esophagus.

These can be symptoms of other problems such as a stomach virus, gastric ulcer, or tropical sprue.

Stomach cancer, also known as gastric cancer, is cancer developing from the lining of the stomach. Early symptoms may include heartburn, upper abdominal pain, nausea and loss of appetite. Later signs and symptoms may include weight loss, yellowing of the skin and whites of the eyes, vomiting, difficulty swallowing, and blood in the stool among others. The cancer may spread from the stomach to other parts of the body, particularly the liver, lungs, bones, lining of the abdomen and lymph nodes.

The most common cause is infection by the bacterium "Helicobacter pylori", which accounts for more than 60% of cases. Certain types of "H. pylori" have greater risks than others. Smoking, dietary factors such as pickled vegetables, and obesity are other risk factors. About 10% of cases run in families and between 1% and 3% of cases are due to genetic syndromes inherited from a person's parents such as hereditary diffuse gastric cancer. Most cases of stomach cancers are gastric carcinomas. This type can be divided into a number of subtypes. Lymphomas and mesenchymal tumors may also develop in the stomach. Most of the time, stomach cancer develops in stages over years. Diagnosis is usually by biopsy done during endoscopy. This is followed by medical imaging to determine if the disease has spread to other parts of the body. Japan and South Korea, two countries that have high rates of the disease, screen for stomach cancer.

A Mediterranean diet lowers the risk of cancer as does the stopping of smoking. There is tentative evidence that treating "H. pylori" decreases the future risk. If cancer is treated early, many cases can be cured. Treatments may include some combination of surgery, chemotherapy, radiation therapy, and targeted therapy. If treated late, palliative care may be advised. Outcomes are often poor with a less than 10% five-year survival rate globally. This is largely because most people with the condition present with advanced disease. In the United States five-year survival is 28% while in South Korea it is over 65% partly due to screening efforts.

Globally, stomach cancer is the fifth leading cause of cancer and the third leading cause of death from cancer making up 7% of cases and 9% of deaths. In 2012, it newly occurred in 950,000 people and caused 723,000 deaths. Before the 1930s, in much of the world, including most Western developed countries, it was the most common cause of death from cancer. Rates of death have been decreasing in many areas of the world since then. This is believed to be due to the eating of less salted and pickled foods as a result of the development of refrigeration as a method of keeping food fresh. Stomach cancer occurs most commonly in East Asia and Eastern Europe. It occurs twice as often in males as in females.

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.

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.

Duodenal cancer is a cancer in the beginning section of the small intestine. It is relatively rare compared to gastric cancer and colorectal cancer. Its histology is usually adenocarcinoma.

Familial adenomatous polyposis (FAP), Gardner syndrome, Lynch syndrome, Muir–Torre syndrome, celiac disease, Peutz–Jeghers syndrome, Crohn's disease and juvenile polyposis syndrome are risk factors for developing this cancer.

The duodenum is the first part of the small intestine. It is located between the stomach and the jejunum. After foods combine with stomach acid, they descend into the duodenum where they mix with bile from the gallbladder and digestive juices from the pancreas.

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.

Diffuse stomach cancer is characterized by the presence of poorly differentiated tumor cells. Microscopic appearance is signet ring cell carcinoma, which is tumor cells with mucin droplet that displaces the nucleus to one side.

The appearance of the stomach is like a "leather bottle". It is characterized by a thick, rigid stomach wall caused by diffuse infiltration of tumor cells and extensive fibrosis.

Diarrhea may be a presenting symptom.

Because liver cancer is an umbrella term for many types of cancer, the signs and symptoms depend on what type of cancer is present. Cholangiocarcinoma is associated with sweating, jaundice, abdominal pain, weight loss and liver enlargement. Hepatocellular carcinoma is associated with abdominal mass, abdominal pain, emesis, anemia, back pain, jaundice, itching, weight loss and fever.

Linitis plastica, also known as Brinton's disease or leather bottle stomach, is a morphological variant of diffuse (or infiltrating) stomach cancer.

Causes of linitis plastica could be lye ingestion or metastatic infiltration of the stomach, particularly breast and lung carcinoma. It is not associated with H. pylori infection or chronic gastritis. The risk factors are undefined, except for rare inherited mutations in E-cadherin, which are found in about 50% of diffuse-type gastric carcinomas.

The most frequent liver cancer, accounting for approximately 75% of all primary liver cancers, is hepatocellular carcinoma (HCC) (also named "hepatoma", which is a misnomer because adenomas are usually benign). HCC is a cancer formed by liver cells, known as hepatocytes, that become malignant. Another type of cancer formed by liver cells is hepatoblastoma, which is specifically formed by immature liver cells. It is a rare malignant tumor that primarily develops in children, and accounts for approximately 1% of all cancers in children and 79% of all primary liver cancers under the age of 15. Most hepatoblastomas form in the right lobe.

Liver cancer can also form from other structures within the liver such as the bile duct, blood vessels and immune cells. Cancer of the bile duct (cholangiocarcinoma and cholangiocellular cystadenocarcinoma) account for approximately 6% of primary liver cancers. There is also a variant type of HCC that consists of both HCC and cholangiocarcinoma. Tumors of the blood vessels (angiosarcoma and hemangioendothelioma, embryonal sarcoma and fibrosarcoma are produced from a type of connective tissue known as mesenchyme. Cancers produced from muscle in the liver are leiomyosarcoma and rhabdomyosarcoma. Other less common liver cancers include carcinosarcomas, teratomas, yolk sac tumours, carcinoid tumours and lymphomas. Lymphomas usually have diffuse infiltration to liver, but It may also form a liver mass in rare occasions.

Many cancers found in the liver are not true liver cancers, but are cancers from other sites in the body that have spread to the liver (known as metastases). Frequently, the site of origin is the gastrointestinal tract, since the liver is close to many of these metabolically active, blood-rich organs near to blood vessels and lymph nodes (such as pancreatic cancer, stomach cancer, colon cancer and carcinoid tumors mainly of the appendix), but also from breast cancer, ovarian cancer, lung cancer, renal cancer, prostate cancer.

Crohn's disease is an inflammatory bowel disease that can affect any part of the digestive tract, even the stomach, although it's a rare presentation. Its main feature is inflammatory ulcers that can affect the total thickness of the stomach wall and can bleed but rarely perforate.

Symptoms include abdominal pain, loss of appetite, and weight loss. Diarrhea is also a symptom that can develop, so checking stools for the appearance of blood is important. It is possible for symptoms of Crohn's disease to remain with a person for weeks or go away on their own. Reporting the symptoms to a doctor is recommended to prevent further complications.

In the stomach there is a slight balance between acid and the wall lining which is protected by mucus. When this mucus lining is disrupted for whatever reason, signs and symptoms of acidity result. This may result in upper abdominal pain, indigestion, loss of appetite, nausea, vomiting and heartburn. When the condition is allowed to progress, the pain may become continuous; blood may start to leak and be seen in the stools. If the bleeding is rapid and of adequate volume it may even result in vomiting of bright red blood (hematemesis). When the acidity is uncontrolled, it can even cause severe blood loss (anemia) or lead to perforation (hole) in the stomach which is a surgical emergency. In many individuals, the progressive bleeding from an ulcer mixes with the feces and presents as black stools. Presence of blood in stools is often the first sign that there is a problem in the stomach.

Hepatoid tumor or hepatoid [adeno]carcinoma are terms for a number of uncommon or rare neoplasms in humans, named for a visual resemblance of the cells under the microscope to those of hepatocellular carcinoma, the most common form of liver cancer. They can arise in several parts of the body, and thus form sub-types of diseases such as stomach cancer and pancreatic cancer. The WHO defines "Hepatoid carcinoma" as "An adenocarcinoma with morphologic characteristics similar to hepatocellular carcinoma , arising from an anatomic site other than the liver".

In dogs it may refer to a Perianal gland tumor, based on a similar resemblance to healthy liver cells.

Most patients with fundic gland polyps (FGPs) do not have any symptoms, and the diagnosis is made on gastroscopy done for other reasons. Retrospective analysis of patients with sporadic FGPs shows that a high percentage do have symptoms, but that this is more likely to be related to the underlying disease responsible for the polyposis. These symptoms include:

- epigastric pain

- nausea

- vomiting

- weight loss

The polyps on endoscopy are usually tiny, numerous and sessile, and usually scattered throughout the fundus of the stomach, where parietal cells are more numerous. They have the same colour as the gastric mucosa, and never have a stalk.

When the polyps are biopsied, the pathology typically shows shortened gastric pits, and both superficial and deep cystic lesions in the fundic glands, lined by all three types of cells of acid-producing mucosa: mucous, parietal and chief cells. As sometimes parietal cell hyperplasia may develop deep dilations of gland, one should be really strict in the diagnosis of FGPs (i.e. the presence of deep and superficial dilations). Infrequently, the two lesions may coexist. Foci of dysplasia can sometimes be seen.

Gastrinoma causes the following symptoms:

- Hypergastrinemia

- Ulcers of the duodenum, stomach, and small intestine.

- Severe diarrhea.

- Generalized cancer symptoms.

The small intestine consists of the duodenum, jejunum and ileum. Inflammation of the small intestine is called enteritis, which if localised to just part is called duodenitis, jejunitis and ileitis, respectively. Peptic ulcers are also common in the duodenum.

Chronic diseases of malabsorption may affect the small intestine, including the autoimmune coeliac disease, infective Tropical sprue, and congenital or surgical short bowel syndrome. Other rarer diseases affecting the small intestine include Curling's ulcer, blind loop syndrome, Milroy disease and Whipple's disease. Tumours of the small intestine include gastrointestinal stromal tumours, lipomas, hamartomas and carcinoid syndromes.

Diseases of the small intestine may present with symptoms such as diarrhoea, malnutrition, fatigue and weight loss. Investigations pursued may include blood tests to monitor nutrition, such as iron levels, folate and calcium, endoscopy and biopsy of the duodenum, and barium swallow. Treatments may include renutrition, and antibiotics for infections.

Diseases that affect the large intestine may affect it in whole or in part. Appendicitis is one such disease, caused by inflammation of the appendix. Generalised inflammation of the large intestine is referred to as colitis, which when caused be the bacteria "Clostridium difficile" is referred to as pseudomembranous colitis. Diverticulitis is a common cause of abdominal pain resulting from outpouchings that particularly affects the colon. Functional colonic diseases refer to disorders without a known cause, and include irritable bowel syndrome and intestinal pseudoobstruction. Constipation may result from lifestyle factors, impaction of a rigid stool in the rectum, or in neonates, Hirschprung's disease.

Diseases affecting the large intestine may cause blood to be passed with stool, may cause constipation, or may result in abdominal pain or a fever. Tests that specifically examine the function of the large intestine include barium swallows, abdominal x-rays, and colonoscopy.

Many people with gastritis experience no symptoms at all. However, upper central abdominal pain is the most common symptom; the pain may be dull, vague, burning, aching, gnawing, sore, or sharp. Pain is usually located in the upper central portion of the abdomen, but it may occur anywhere from the upper left portion of the abdomen around to the back.

Other signs and symptoms may include the following:

- Nausea

- Vomiting (if present, may be clear, green or yellow, blood-streaked, or completely bloody, depending on the severity of the stomach inflammation)

- Belching (if present, usually does not relieve the pain much)

- Bloating

- Early satiety

- Loss of appetite

- Unexplained weight loss

A gastrinoma is a tumor in the pancreas or duodenum that secretes excess of gastrin leading to ulceration in the duodenum, stomach and the small intestine. There is hypersecretion of HCl acid into the duodenum, which causes the ulcers. Excessive HCl acid production also causes hyperperistalsis, and inhibits the activity of lipase, causing severe diarrhea.

It is frequently the source of the gastrin in Zollinger-Ellison syndrome.

It is usually found in the duodenum, although it may arise in the stomach or pancreas. Those occurring in the pancreas have a greater potential for malignancy. Most gastrinomas are found in the gastrinoma triangle; this is bound by the junction of cystic and common bile ducts, junction of the second and third parts of the duodenum, and the junction of the neck and body of the pancreas.

Early signs and symptoms of ovarian cancer may be absent or subtle. In most cases, symptoms exist for several months before being recognized and diagnosed. Symptoms can be misdiagnosed as irritable bowel syndrome. The early stages of ovarian cancer tend to be painless. Symptoms can vary based on the subtype. Low malignant potential (LMP) tumors, also known as borderline tumors, do not cause an increase in CA125 levels and are not identifiable with an ultrasound. The typical symptoms of an LMP tumor can include abdominal distension or pelvic pain. Particularly large masses tend to be benign or borderline.

The most typical symptoms of ovarian cancer include bloating, abdominal or pelvic pain or discomfort, back pain, irregular menstruation or postmenopausal vaginal bleeding, pain or bleeding after or during sexual intercourse, loss of appetite, fatigue, diarrhea, indigestion, heartburn, constipation, nausea, feeling full, and possibly urinary symptoms (including frequent urination and urgent urination).

The growing mass may cause pain if ovarian torsion develops. Symptoms can be caused by a mass pressing on the other abdominopelvic organs or from metastases. If these symptoms start to occur more often or more severely than usual, especially after no significant history of such symptoms, ovarian cancer is considered. Metastases may cause a Sister Mary Joseph nodule. Rarely, teratomas can cause growing teratoma syndrome or peritoneal gliomatosis. Some experience menometrorrhagia and abnormal vaginal bleeding after menopause in most cases. Other common symptoms include hirsutism, abdominal pain, virilization, and an adnexal mass.

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.

Common causes include "Helicobacter pylori" and NSAIDs. Less common causes include alcohol, cocaine, severe illness and Crohn disease, among others.

Patients with atrophic gastritis are also at increased risk for the development of gastric adenocarcinoma. The optimal endoscopic surveillance strategy is not known but all nodules and polyps should be removed in these patients.

Atrophic gastritis (also known as Type A or Type B Gastritis more specifically) is a process of chronic inflammation of the stomach mucosa, leading to loss of gastric glandular cells and their eventual replacement by intestinal and fibrous tissues. As a result, the stomach's secretion of essential substances such as hydrochloric acid, pepsin, and intrinsic factor is impaired, leading to digestive problems. The most common are vitamin B deficiency which results in a megaloblastic anemia and malabsorbtion of iron, leading to iron deficiency anaemia. It can be caused by persistent infection with "Helicobacter pylori", or can be autoimmune in origin. Those with the autoimmune version of atrophic gastritis are statistically more likely to develop gastric carcinoma, Hashimoto's thyroiditis, and achlorhydria.

Type A gastritis primarily affects the body/fundus of the stomach, and is more common with pernicious anemia.

Type B gastritis primarily affects the antrum, and is more common with "H. pylori" infection.