The stomach

The stomach is part of the digestive system, which is sometimes called the gastrointestinal tract. It is a muscular, bag-like organ which lies between the lower end of the gullet (oesophagus) and the beginning of the small bowel (small intestine). Once food has been swallowed it passes down the gullet and into the stomach.

The position of the stomach

The wall of the stomach has four layers:
The inner lining (the mucosa) contains glands. The glands produce chemicals (enzymes and acid) which are released into the stomach and help to break down food so that when it leaves the stomach it is in a semi-solid form.
Underneath the mucosa is a layer called the submucosa. Beneath that is a layer of muscle called the muscularis.
The outer layer of the stomach is a strong membrane called the serosa.

Structure of the stomach wall

The stomach lining also produces a substance which helps to absorb vitamin B12. This is important for the development of red blood cells.

Close to the stomach are a number of lymph nodes.

What is cancer?

The organs and tissues of the body are made up of tiny building blocks called cells. Cancer is a disease of these cells.

Cells in different parts of the body may look and work differently but most reproduce themselves in the same way. Cells are constantly becoming old and dying, and new cells are produced to replace them. Normally, cells divide in an orderly and controlled manner. If for some reason the process gets out of control, the cells carry on dividing, developing into a lump which is called a tumour.

Tumours can be either benign or malignant. Cancer is the name given to a malignant tumour. Doctors can tell if a tumour is benign or malignant by examining a small sample of cells under a microscope. This is called a biopsy.

In a benign tumour the cells do not spread to other parts of the body and so are not cancerous. However, if they continue to grow at the original site, they may cause a problem by pressing on the surrounding organs.

A malignant tumour consists of cancer cells that have the ability to spread beyond the original area. If the tumour is left untreated, it may spread into and destroy surrounding tissue. Sometimes cells break away from the original (primary) cancer. They may spread to other organs in the body through the bloodstream or lymphatic system.

The lymphatic system is part of the immune system - the body's natural defence against infection and disease. It is a complex system made up of organs, such as bone marrow, the thymus, the spleen, and lymph nodes. The lymph nodes (or glands) throughout the body are connected by a network of tiny lymphatic ducts.

When the cancer cells reach a new area they may go on dividing and form a new tumour. This is known as a secondary cancer or metastasis.

It is important to realise that cancer is not a single disease with a single type of treatment. There are more than 200 different kinds of cancer, each with its own name and treatment.

Types of cancer

Carcinomas

The majority of cancers, about 85% (85 in a 100), are carcinomas. They start in the epithelium, which is the covering (or lining) of organs and of the body (the skin). The common forms of breast, lung, prostate and bowel cancer are all carcinomas.

Carcinomas are named after the type of epithelial cell that they started in and the part of the body that is affected. There are four different types of epithelial cells:
squamous cells - that line different parts of the body, such as the mouth, gullet (oesophagus), and the airways
adeno cells - form the lining of all the glands in the body and can be found in organs such as the stomach, ovaries, kidneys and prostate
transitional cells - are only found in the lining of the bladder and parts of the urinary system
basal cells - that are found in one of the layers of the skin.

A cancer that starts in squamous cells is called a squamous cell carcinoma. A cancer that starts in glandular cells is called an adenocarcinoma. Cancers that start in transitional cells are transitional cell carcinomas, and those that start in basal cells are basal cell carcinomas.

Leukaemias and lymphomas

These occur in the tissues where white blood cells (which fight infection in the body) are formed, i.e. the bone marrow and lymphatic system. Leukaemia and lymphoma are quite rare and make up about 6.5% (6.5 in 100) of all cancers.

Sarcomas

Sarcomas are very rare. They are a group of cancers that form in the connective or supportive tissues of the body such as muscle, bone and fatty tissue. They account for less than 1% (1 in 100) of cancers.

Sarcomas are split into two main types:

bone sarcomas - that are found in the bones

soft tissue sarcomas - that develop in the other supportive tissues of the body.

Others forms of cancer

Brain tumours and other very rare forms of cancer make up the remainder of cancers.

Types of stomach cancer

Around 9200 people are diagnosed with stomach cancer in the UK each year. There are several different types of stomach cancer, some of which are very rare.

The most common types of stomach cancer start in the glandular cells of the stomach lining and are known as adenocarcinomas.

Other types of cancer that can affect the stomach are soft tissue sarcomas. These are rare cancers that usually start from the cells of the muscle layer of the stomach. The most common type of sarcoma to affect the stomach is a leiomyosarcoma.

Another type of sarcoma is a gastrointestinal stromal tumour (GIST). These cancers start in the tissues that support the organs of the digestive system. GISTs behave differently from other types of sarcoma and are treated very differently.

Another rare type of tumour that can affect the stomach is a lymphoma. Lymphomas are cancers of the lymphatic system. The main type to affect the stomach is a MALT lymphoma (also known as a MALToma).

The stomach can also be affected by a type of tumour known as a carcinoid tumour.