Stomach cancer (also referred to as gastric cancer) is cancer of the stomach. Cancer occurs when normal cells lose their ability to self-regulate and grow into an abnormal mass, or tumor. Unlike benign tumors, which are not life threatening, cancerous (or malignant) tumors can invade neighboring tissues, or spread to distant organs (metastasize) via the body’s circulatory system. Patient prognosis is highly dependent on the extent of cancer spread at the time of diagnosis.
The stomach wall consists of five layers: mucosa, submucosa, muscle, subserosa, and serosa. Stomach cancer usually originates in the mucus-producing cells of the innermost layer, where it is called adenocarcinoma - the most common of stomach cancers. Other types of stomach cancers originate in immune cells (lymphomas), endocrine cells (carcinoids), or rarely, cells of the nervous system (gastrointestinal stromal tumor).
Stomach cancer is a leading cause of cancer-related deaths worldwide. In the United States, roughly 22,220 new cases of stomach cancer are expected in 2014.
Causes and Risk Factors
The underlying cause of all cancers is an error (or mutation) in the cell’s DNA that alters the function of the affected gene. It is common for genomes of cancer cells to accumulate a number of mutations as they proliferate. Certain gene mutations impair the regulatory mechanisms that control cell number and survival, allowing uncontrolled cell proliferation. Although the exact mechanism behind disease onset is not clear, the following risk factors are associated with stomach cancer:
Helicobacter pylori (H. pylori). H. pylori is a Gram-negative bacterium that infects and damages the mucus lining of the stomach, making it prone to peptic ulcers. H. pylori infection also increases the risk of stomach cancer.
Inflammation. Long-term inflammation of the stomach, which occurs with pernicious anemia or following a gastrectomy, is associated with stomach cancer.
Life habits. A higher risk of developing stomach cancer is associated with obesity; lack of physical activity; smoking; and a diet low in fruits and vegetables, but high in pickled, smoked, and salty foods.
Age and gender. Stomach cancer is most common in individuals over the age 65, and affects men more than women.
Family history. Genetic factors that make someone prone to a particular disease can be inherited. Therefore, a person’s chances of developing stomach cancer increases if close family or relatives have the disease.
As stomach cancer grows it can produce the following symptoms:
Stomach pain and discomfort
Persistent nausea and vomiting
Feeling full or bloated after small meals
Severe heartburn and indigestion
Fluid accumulation in the stomach
Sudden weight loss
Diagnosis and Treatment
In patients experiencing symptoms, stomach cancer is diagnosed using techniques that visualize the gastrointestinal (GI) tract, and remove samples for testing.
Physical exam. A doctor or gastroenterologist performs a physical exam to feel for abnormalities in the stomach and lymph nodes. The family history of stomach cancer and other risk factors are also discussed.
Upper endoscopy. An esophagogastroduodenoscopy (EDG), also known as upper endoscopy, is performed to look for tumors. During an EDG a small, lighted camera is delivered down the GI tract using a long flexible tube. Usually a small tissue sample is removed (biopsy) to confirm cancer is present and to determine the type (e.g., adenocarcinoma, carcinoid, gastrointestinal stromal tumor, or lymphoma).
Imaging. Tumors can be detected using a computerized tomography (CT) scan or X-ray imaging. Prior to a CT scan, the patient receives an oral or intravenous contrast agent to aid visualization. The contrast agent for an X-ray is a thick chalky liquid containing barium (also known as “barium swallow”).
Following a positive diagnosis, the cancer is “staged” to determine the extent of spreading within the stomach, and to other organs. Staging requires a close examination of the stomach and other organs using imaging techniques and surgery. Specific laboratory tests are also performed to assess blood counts and key bodily functions.
Imaging. The stomach and other organs are inspected in detail using a CT scan or X-ray imaging. A chest X-ray inspects the lungs for tumors, while a CT scan can detect tumors in the liver, pancreas, and other organs.
Endoscopic ultrasound. A probe that emits sound waves is delivered down the GI tract using a thin tube. The emitted sound waves bounce off the organs, and a computer translates the resulting echo pattern into an image. This technique is used to evaluate the stomach wall and nearby lymph nodes.
Laparoscopy. This minimally invasive surgical procedure is used to examine the stomach wall, nearby lymph nodes, and remove samples when necessary. During a laparoscopy, instruments are delivered to the surgery site through thin tubes inserted into the abdomen.
The stages of adenocarcinoma range from 1-4 (represented as Roman numerals I-IV). Stage 0 indicates the cancer is confined to the inner mucus lining of the stomach.
Stage I: The cancer has spread mainly to the submucosa layer, and/or a few nearby lymph nodes.
Stage II: The cancer has spread to the muscle layer, and/or more lymph nodes.
Stage III: The cancer has spread through all layers of the stomach wall, many lymph nodes, and/or possibly nearby organs.
Stage IV: The cancer has spread to nearby organs and/or many lymph nodes, and metastasized to distant organs.
The choice of treatment is highly dependent on tumor size and location, disease stage, and extent of metastasis. In general, cancer treatment involves killing and/or removing the cancerous cells. Early-stage cancer has the highest chance of a favorable prognosis. The 5-year survival rates for stomach cancer range from 71% (stages I) to 4% (stage IV). Many patients live longer than 5 years or are cured.
Surgery. Depending on the location of the tumor, surgery is performed to remove the stomach (gastrectomy), either partially or completely. In partial gastrectomy, the affected lower part of the stomach is removed, while in total gastrectomy the entire stomach and parts of nearby organs are removed.
Chemotherapy. Chemotherapy is a systemic drug therapy aimed at killing cancer cells at the original site, and those that have spread to other sites. The drugs work by targeting rapidly dividing cells, like cancer cells. Common side effects of chemotherapy are due to inadvertent toxicity to blood cells, and cells of the hair root and digestive tract, all of which are also rapidly diving. Chemotherapy is often used in combination with surgery.
Radiation. Radiation or radiotherapy targets and kills all cells, including cancers, with high-energy radiation. It is usually applied locally and in combination with surgery and/or chemotherapy.
Targeted drugs. In addition to the above therapies, cancer cells with specific characteristics can be targeted with drugs. For example, Herceptin® (trastuzumab) is a humanized antibody that targets cancer cells over-producing the growth-promoting protein HER2, and inhibits proliferation.
Experimental therapies. Patients who cannot benefit from available treatment options may choose to participate in studies, or clinical trials, of treatments that are not yet approved for prescription to the public. Information about available clinical trials as well as the associated risks and benefits is available through medical providers.
The risks of developing stomach cancer may be reduced by not smoking; maintaining a heathy weight; and adhering to a diet that is high in fruits and vegetables, but low in salty, pickled, and smoked foods. Individuals with a family history of stomach cancer may consult their doctor regarding screening options for early detection.
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“Stomach Cancer”. Mayo Clinic. Mayo Foundation for Medical Education and Research. Apr 2014. Retrieved May 8, 2014. http://www.mayoclinic.org/diseases-conditions/stomach-cancer/basics/definition/con-20038197.