What is a stomach cancer?
Stomach cancer or gastric cancer is a type of malignant tumor that develops in the stomach-the muscular J-shaped sac located in the upper middle of your abdomen, just below the ribs. It occurs when an abnormal groups of cells, known as a tumor, develops inside the stomach. Stomach cancers are caused by Helicobacter pylori infection that starts in lining that form the innermost layer, the mucosa. They may cause different symptomps and tend to have different outcomes. They can also metastasize in different ways- can grow through the walls of the stomach and even invade the nearby organs. They can also spread to the lymph vessels and nearby lymph nodes. There are 6 main types of stomach cancer (gastric cancer) which include:
By far, most cancers of the stomach (90 to 95%) are a type known as adenocarcinomas. This type of cancer starts and develops in the glandular tissues. Gastric adenocarcinoma is divided into two subtypes i.e. intestinal and diffuse.
Intestinal adenocarcinoma usually evolves in parts of the stomach closer to the intestines and more frequently affects people over the age of 80. It starts in the gland cells in the stomach lining. The gland cells are the cells that form the stomach lining and are responsible for the production of mucus and stomach juices. The symptoms of Intestinal adenocarcinoma are, however, often vague.
The most common symptoms of adenocarcinoma include:
- Pain in the abdomen
- Weakness and fatigue
- Weight loss
As the tumor gets larger, it can start to block the passage of the digested food leading to intense and long-lasting abdominal pain, and if it is not contained in its early stages, it may lead to a condition known as obstruction- a complete blockage of the intestine, meaning nothing can move through. This condition leads to increased pain with severe nausea and vomiting.
Mucosa-associated lymphoid tissue lymphomas (or MALT lymphomas), do not start in the lymph nodes. They develop in the lymphatic tissue (the tissue that drains away fluid and helps fight infection) which is made up of immune system cells in the walls of the stomach.
The lymphoma of the stomach is a very rare condition and only makes up approximately 4% of stomach cancers. According to the American Cancer Society, lymphomas can grow slowly or can be very aggressive.
Symptoms of lymphomas include:
- Epigastric pain
- Early satiety
- Weight loss
Gastrointestinal Stromal Tumor (GIST)
This type of stomach cancer develops in the tissues which support the digestive organs which comprise the oesophagus, stomach, liver, gall bladder, ileum (small intestine), colon (large intestine), rectum and lining of the gut. It starts in the very early forms of special cells found in the wall of the gastrointestinal (GI) tract, called the interstitial cells of Cajal (or ICCs). ICCs are cells of the autonomic nervous system i.e. the part of the nervous system that regulates body processes such as food digestion, and intake of nutrients (minerals, fats, vitamins, proteins, carbohydrates, and water). GISTs may be malignant (cancer) or benign (not cancer).
Possible symptoms of GIST include:
- Severe pain in the abdomen
- Blood (either bright red or very dark) in the stool or vomit
- Feeling satiated early after only a little food is eaten
- Trouble or pain when swallowing
Gastrointestinal Carcinoid tumors
Carcinoid tumor is another less common form of stomach cancer that develops in the neuroendocrine cells- the hormone-producing cells of the stomach. These cells are also involved in the control of releasing digestive juices, and aid in helping food travel through the gastrointestinal tract. Most of these tumors do not, however, spread to other organs and accounts for only 3% of stomach cancer incidences. They are slow-growing, but in some cases metastasis may occur.
Carcinoid tumors of the mid-gut (which comprise jejunum, ileum, cecum and appendix) are associated with carcinoid syndrome.
Symptoms of GI Carcinoid tumor include:
- Peripheral edema
- Abdominal cramping
Squemous cell cancer
Squemous cell carcinoma (SCC) is the skin like cells that lie between gland cells to make the stomach lining. It is an uncontrolled growth of abnormal cells arising in the squemous cells, which compose most of the skin’s upper layers (the epidermis), the upper part of the oesophagus and the end of the anus. SCC of the stomach is a rare occurance, accounting for nearly 0.2% of all gastric carcinomas.
This is a very uncommon condition that rarely spreads to the lymph nodes and accounts for between 5-10% of all soft tissue sarcomas. It arises from smooth muscle cells in muscularis mucosa or propia of the stomach lining that are responsible for the wave-like contractions (or peristalsis) that aid in the digestion and transport of food.
Smooth muscles are involuntary muscles i.e. the brain has no control over them and since they are found all over the body, a leiomyosarcoma can form almost anywhere where there are blood vessels, liver, heart, genitourinary tract, pancreas and gastrointestinal tract.