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.

Prominent symptoms usually do not appear until the cancer has infiltrated over 60% of the circumference of the esophageal tube, by which time the tumor is already in an advanced stage. Onset of symptoms is usually caused by narrowing of the tube due to the physical presence of the tumor.

The first and the most common symptom is usually difficulty in swallowing, which is often experienced first with solid foods and later with softer foods and liquids. Pain when swallowing is less usual at first. Weight loss is often an initial symptom in cases of squamous-cell carcinoma, though not usually in cases of adenocarcinoma. Eventual weight loss due to reduced appetite and undernutrition is common. Pain behind the breastbone or in the region around the stomach often feels like heartburn. The pain can frequently be severe, worsening when food of any sort is swallowed. Another sign may be an unusually husky, raspy, or hoarse-sounding cough, a result of the tumor affecting the recurrent laryngeal nerve.

The presence of the tumor may disrupt the normal contractions of the esophagus when swallowing. This can lead to nausea and vomiting, regurgitation of food and coughing. There is also an increased risk of aspiration pneumonia due to food entering the airways through the abnormal connections (fistulas) that may develop between the esophagus and the trachea (windpipe). Early signs of this serious complication may be coughing on drinking or eating. The tumor surface may be fragile and bleed, causing vomiting of blood. Compression of local structures occurs in advanced disease, leading to such problems as upper airway obstruction and superior vena cava syndrome. Hypercalcemia (excess calcium in the blood) may occur.

If the cancer has spread elsewhere, symptoms related to metastatic disease may appear. Common sites of spread include nearby lymph nodes, the liver, lungs and bone. Liver metastasis can cause jaundice and abdominal swelling (ascites). Lung metastasis can cause, among other symptoms, impaired breathing due to excess fluid around the lungs (pleural effusion), and dyspnea (the feelings often associated with impaired breathing).

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.

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.

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.

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.

Esophageal cancer is cancer arising from the esophagus—the food pipe that runs between the throat and the stomach. Symptoms often include difficulty in swallowing and weight loss. Other symptoms may include pain when swallowing, a hoarse voice, enlarged lymph nodes ("glands") around the collarbone, a dry cough, and possibly coughing up or vomiting blood.

The two main sub-types of the disease are esophageal squamous-cell carcinoma (often abbreviated to ESCC), which is more common in the developing world, and esophageal adenocarcinoma (EAC), which is more common in the developed world. A number of less common types also occur. Squamous-cell carcinoma arises from the epithelial cells that line the esophagus. Adenocarcinoma arises from glandular cells present in the lower third of the esophagus, often where they have already transformed to intestinal cell type (a condition known as Barrett's esophagus). Causes of the squamous-cell type include tobacco, alcohol, very hot drinks, poor diet, and chewing betel nut. The most common causes of the adenocarcinoma type are smoking tobacco, obesity, and acid reflux.

The disease is diagnosed by biopsy done by an endoscope (a fiberoptic camera). Prevention includes stopping smoking and eating a healthy diet. Treatment is based on the cancer's stage and location, together with the person's general condition and individual preferences. Small localized squamous-cell cancers may be treated with surgery alone with the hope of a cure. In most other cases, chemotherapy with or without radiation therapy is used along with surgery. Larger tumors may have their growth slowed with chemotherapy and radiation therapy. In the presence of extensive disease or if the affected person is not fit enough to undergo surgery, palliative care is often recommended.

As of 2012, esophageal cancer was the eighth-most common cancer globally with 456,000 new cases during the year. It caused about 400,000 deaths that year, up from 345,000 in 1990. Rates vary widely among countries, with about half of all cases occurring in China. It is around three times more common in men than in women. Outcomes are related to the extent of the disease and other medical conditions, but generally tend to be fairly poor, as diagnosis is often late. Five-year survival rates are around 13% to 18%.

Hereditary nonpolyposis colorectal cancer (HNPCC) or Lynch syndrome is an autosomal dominant genetic condition that has a high risk of colon cancer as well as other cancers including endometrial cancer (second most common), ovary, stomach, small intestine, hepatobiliary tract, upper urinary tract, brain, and skin. The increased risk for these cancers is due to inherited mutations that impair DNA mismatch repair. It is a type of cancer syndrome.

Signet ring cell carcinoma (SRCC) is a rare form of highly malignant adenocarcinoma that produces mucin. It is an epithelial malignancy characterized by the histologic appearance of signet ring cells.

Primary SRCC tumors are most often found in the glandular cells of the stomach (SRCC originates in the stomach in 90 percent of patients), and less frequently in the breast, gallbladder, urinary bladder, and pancreas. SRCCs do not normally form in the lungs, though a few incidences have been reported.

Among colorectal cancers, the prevalence of SRCC is less than one percent. Though incidence and mortality of gastric cancer has declined in many countries over the past 50 years, there has been an increase in occurrences of gastric SRCC-type cancers.

SRCC tumors grow in characteristic sheets, which makes diagnosis using standard imaging techniques, like CT and PET scans, less effective.

Individuals with HNPCC have about an 80% lifetime risk for colon cancer. Two-thirds of these cancers occur in the proximal colon. The mean age of colorectal cancer diagnosis is 44 for members of families that meet the Amsterdam criteria. Also, women with HNPCC have an 80% lifetime risk of endometrial cancer. The average age of diagnosis of endometrial cancer is about 46 years. Among women with HNPCC who have both colon and endometrial cancer, about half present first with endometrial cancer, making endometrial cancer the most common sentinel cancer in Lynch syndrome. In HNPCC, the mean age of diagnosis of gastric cancer is 56 years of age with intestinal-type adenocarcinoma being the most commonly reported pathology. HNPCC-associated ovarian cancers have an average age of diagnosis of 42.5 years-old; approximately 30% are diagnosed before age 40. Other HNPCC-related cancers have been reported with specific features: the urinary tract cancers are transitional carcinoma of the ureter and renal pelvis; small bowel cancers occur most commonly in the duodenum and jejunum; the central nervous system tumor most often seen is glioblastoma.

A large follow up study (3119 patients; average follow up 24 years) has found significant variation in the cancer rates depending on the mutation involved. Up to the age of 75 years the risks of colorectal cancer, endometrial cancer, ovarian cancer, upper gastrointestinal (gastric, duodenal, bile duct or pancreatic), urinary tract cancers, prostate cancer and brain tumours were as follows: for MLH1 mutations the risk was - 46%, 43%, 10%, 21%, 8%, 17% and 1% respectively: for MSH2 mutations the risks were 57%, 17%, 10%, 25%, 32%, and 5% respectively: for MSH6 mutations the risks were 15%, 46%, 13%, 7%, 11%, 18% and 1% respectively.

Hereditary diffuse gastric cancer is an inherited genetic syndrome caused by a change in the E-cadherin gene. It often results in stomach cancer such that it is recommended that those who carry the gene have their stomach removed.

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

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.

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.

Primary signet ring cell carcinoma of the colon and rectum (PSRCCR) is rare, with a reported incidence of less than 1 percent. It has a poor prognosis because symptoms often develop late and it is usually diagnosed at an advanced stage. Five-year survival rates in previous studies ranged from nine to 30 percent. Average survival was between 20 and 45 months. It tends to affect younger adults with higher likelihood of lymphovascular invasion. It is worth noting that the overall survival rate of patients with SRCC was significantly poorer than that of patients with mucinous or poorly differentiated adenocarcinoma.

In advanced gastric cancers, the prognosis for patients with the SRCCs was significantly worse than for the other histological types, which can be explained by the finding that advanced SRCC gastric cancers have a larger tumor size, more lymph node metastasis, a deeper invasive depth and more Borrmann type 4 lesions than other types.

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.

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

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.

Krukenberg tumors often come to the attention when they cause abdominal or pelvic pain, bloating, ascites, or pain during sexual intercourse. Krukenberg tumors can occasionally provoke a reaction of the ovarian stroma which leads to hormone production, that results in vaginal bleeding, a change in menstrual habits, or hirsutism, or occasionally virilization as a main symptom.

All these symptoms are non-specific and can also arise with a range of problems other than cancer, and a diagnosis can only be made following confirmatory investigations such as computed tomography (CT) scans, laparotomy and/or a biopsy of the ovary.

The change from normal to premalignant cells that indicate Barrett's esophagus does not cause any particular symptoms. Barrett's esophagus, however, is associated with these symptoms:

- frequent and longstanding heartburn

- trouble swallowing (dysphagia)

- vomiting blood (hematemesis)

- pain under the sternum where the esophagus meets the stomach

- unintentional weight loss because eating is painful (odynophagia)

The risk of developing Barrett's esophagus is increased by central obesity (vs. peripheral obesity). The exact mechanism is unclear. The difference in distribution of fat among men (more central) and women (more peripheral) may explain the increased risk in males.

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.

Barrett's esophagus refers to an abnormal change (metaplasia) in the cells of the lower portion of the esophagus. It is characterized by the replacement of the normal stratified squamous epithelium lining of the esophagus by simple columnar epithelium with goblet cells (which are usually found lower in the gastrointestinal tract). The medical significance of Barrett's esophagus is its strong association (0.1 per 1 cm Prague C>M> total segment length per patient-year) with esophageal adenocarcinoma, a very often deadly cancer, because of which it is considered to be a premalignant condition.

The main cause of Barrett's esophagus is thought to be an adaptation to chronic acid exposure from reflux esophagitis. The incidence of esophageal adenocarcinoma has increased substantially in the Western world in recent years. The condition is found in 5–15% of patients who seek medical care for heartburn (gastroesophageal reflux disease), although a large subgroup of patients with Barrett's esophagus do not have symptoms. Diagnosis requires endoscopy (more specifically, esophagogastroduodenoscopy, a procedure in which a fibreoptic cable is inserted through the mouth to examine the esophagus, stomach, and duodenum) and biopsy. The cells of Barrett's esophagus, after biopsy, are classified into four general categories: nondysplastic, low-grade dysplasia, high-grade dysplasia, and frank carcinoma. High-grade dysplasia and early stages of adenocarcinoma can be treated by endoscopic resection and new endoscopic therapies such as radiofrequency ablation, whereas advanced stages (submucosal) are generally advised to undergo surgical treatment. Nondysplastic and low-grade patients are generally advised to undergo annual observation with endoscopy, with radiofrequency ablation as a therapeutic option. In high-grade dysplasia, the risk of developing cancer might be at 10% per patient-year or greater.

The condition is named after the Australian-born British thoracic surgeon Norman Barrett (1903–1979), who described it in 1950.

Those with the eating disorder bulimia are more likely to develop Barrett’s esophagus because bulimia can cause severe acid reflux, and because purging also floods the esophagus with acid.

Several other terms for this lesion have been used in the past medical literature, including mucinous multilocular cyst carcinoma, pseudomyxomatous pulmonary adenocarcinoma, mucinous cystic tumor of low malignant potential, and others.

From early adolescence, patients with this condition gradually (and much of the time 'silently') develop hundreds to thousands of colorectal polyps (and sometimes polyps elsewhere)—small abnormalities at the surface of the intestinal tract, especially in the large intestine including the colon or rectum. These may bleed, leading to blood in the stool. If the blood is not visible, it is still possible for the patient to develop anemia due to gradually developing iron deficiency. If malignancy develops, this may present with weight loss, altered bowel habit, or even metastasis to the liver or elsewhere. FAP can also develop 'silently' in some individuals, giving few or no signs until it has developed into advanced colorectal cancer.

Because familial polyposis develops very gradually over years, and can also manifest in an 'attenuated' form even more gradually, polyps resulting from FAP can lead to cancer developing at any point from adolescence to old age.

Depending on the nature of the defect in the APC gene, and whether it is the full or attenuated form, familial polyposis may manifest as polyps in colon or in the duodenal tract, or in any combination of these. Therefore, an absence of polyps in, for example, the rectum, may not of itself be sufficient to confirm absence of polyps. It may be necessary to consider and visually examine other possible parts of the intestinal tract. Colonoscopy is preferred over sigmoidoscopy for this, as it provides better observation of the common right-side location of polyps.

The genetic determinant in familial polyposis may also predispose carriers to other malignancies, e.g., of the duodenum and stomach (particularly ampullary adenocarcinoma). Other signs that may point to FAP are pigmented lesions of the retina ("CHRPE—congenital hypertrophy of the retinal pigment epithelium"), jaw cysts, sebaceous cysts, and osteomata (benign bone tumors). The combination of polyposis, osteomas, fibromas and sebaceous cysts is termed "Gardner's syndrome" (with or without abnormal scarring).

This particular variant of lung cancer is usually asymptomatic and is found after chest x-rays are taken for other reasons. Hemoptysis is seen occasionally and, in some cases, distal obstruction of bronchi by blood clots or mucus plugs produces cough and/or infection. Lesions often enlarge and progress slowly, over many years.

The 1999 World Health Organization classification system defined MCACL as a cystic adenocarcinoma with copious mucin production that, histologically, resembles (the more common) mucus-producing cystadenocarcinomas originating in the ovary, breast and pancreas. The 2004 revision of the WHO classification noted that the tumors tend to be well circumscribed by a partial fibrous tissue capsule with central cystic change and copious mucin pooling. The thin, fibrous wall circumscribing the tumor is highly characteristic of this lesion. It can sometimes occur within a pulmonary bronchocele, and this tumor entity should be kept in mind after identification of a bronchocele with suspicious or non-prototypical imaging characteristics.

Microscopically, the neoplastic epithelial cells tend to grow along the alveolar walls, in a fashion similar to the mucinous variant of bronchioloalveolar carcinoma, a more common form of adenocarcinoma.

Hemoptysis is seen occasionally.

Positron Emission Tomography (PET) scanning can be of assistance in diagnosing MCACL, as these lesions show intense uptake, typically in the wall of the tumor.

CA 19-9 has been reported to be elevated in MCACL.

Differential diagnosis of MCACL includes secondary metastatic cystadenocarcinomatous lesions, particularly from the pancreas or ovary, mucoepidermoid carcinoma, and pulmonary mucinous bronchioloalveolar carcinoma. The mouse monoclonal antibody 1D3, developed to detect a high molecular weight mucin found in a number of cystic malignancies of various organs, may be of use in differentiating primary mucinous cystadenocarcinoma of the lung from metastatic lung tumors due to mucinous cystic lesions of the uterus and pancreas, as well as those primary in the colon and stomach.