Stomach Cancer

What is cancer?

Cancer cells are damaged cells that ignore signals to repair themselves or die. They grow and divide far faster than normal cells, forming a tumour. Unlike healthy cells, they can hide from the immune system and continue multiplying unchecked.

As they change further, cancer cells may lose the ‘stickiness’ that keeps them attached to other cancer cells. This allows them to break away and travel through the body to form new growths elsewhere.

Our cells and genes

The cells in our bodies contain around 20,000 genes, which are contained within our DNA. Each gene acts like an instruction, telling cells when to grow, divide or repair themselves. Our genes receive signals from inside and around the cell that tell them when to switch on or off.

We inherit some gene changes (mutations) from our parents. Most are harmless, but a few increase the risk of certain cancers. These inherited changes, called germline mutations, are present in every cell of our body.

Throughout our lifetimes, cells in our bodies change due to ageing, environmental factors such as pollution, and lifestyle factors such as smoking or obesity. These gene changes are called somatic mutations. They happen during life, not at birth. Most cause no harm, but occasionally a mutation can make a cell turn into a cancer cell.

How cancer spreads

When cancer spreads to another part of the body, it is called metastasis. There are three main ways it spreads.

The bloodstream

To grow, tumours create their own blood supply. This process is called angiogenesis. Some cancer cells lose their ability to stick to other cells, they then detach and enter the bloodstream. They can then travel, settle and grow in distant organs such as the liver or lungs. This is called haematogenous (through the blood) spread.

The lymphatic system

The lymphatic system is a network of vessels that drains fluid and carries immune cells. Cancer cells can enter nearby lymph vessels and travel to lymph nodes (glands) positioned along them. The first nodes affected are usually near the stomach, but over time, cancer can spread to distant nodes. This pattern of spread is called lymphatic metastasis. Cancer in nearby lymph nodes is often one of the earliest signs that cancer is beginning to spread.

The abdomen (peritoneum)                                  

If the tumour grows through the stomach wall and reaches the outer surface, cancer cells can shed directly into the abdomen, where they can move through the fluid which keeps the organs moist. The cancer cells may attach to the peritoneum (the sac that protects the organs) or to the surfaces of other organs, such as the bowel or ovaries. This is called transcoelomic spread or peritoneal disease.

Types of cancer in the stomach

Several types of cancers can start in the stomach.

Gastric adenocarcinoma

Around 95% (more than 9 in 10) stomach cancers are gastric adenocarcinoma, which begin in the glandular cells of the stomach lining (mucosa). This is the type of cancer doctors mean when they say stomach cancer or gastric cancer.

All material on the Stomach Cancer UK website is about gastric adenocarcinoma unless stated otherwise.

Lymphoma

Gastric MALT lymphoma (Mucosa-Associated Lymphoid Tissue lymphoma) is a rare cancer that starts in B lymphocytes (a type of immune cell) within the stomach lining. It tends to grow slowly and mainly affects people over 60.

Diffuse Large B-Cell Lymphoma (DLBCL) is a faster-growing form that can occasionally start in the stomach or develop from a MALT lymphoma.

Together, these gastric lymphomas account for fewer than 5 % (5 in 100) of cancers that start in the stomach. Their treatment and outlook differ from those of gastric adenocarcinoma.

Gastric adenocarcinoma that has spread to many lymph nodes, or to distant nodes in the chest or neck, can resemble lymphoma at first. Testing the tumour (biopsy samples) will show which type of cancer it is.

For more information about gastric lymphomas, visit Lymphoma Action

Gastric neuroendocrine neoplasms (NENs)

These rare cancers start in the hormone-producing cells of the stomach.

Gastric neuroendocrine tumours (NETs) are usually slow-growing and often appear as raised growths or polyps on the stomach lining. They include what were once known as carcinoid tumours.

Gastric neuroendocrine carcinomas (NECs) arise from the same cell type but can be more aggressive and high-grade.

Gastric NENs account for about 2% (2 in 100) of cancers which start in the stomach. Their treatment and outlook differ from gastric adenocarcinoma. For further information and support, visit Neuroendocrine Cancer UK

Gastrointestinal stromal tumours (GIST)

GIST is a slow-growing sarcoma that begins in the submucosa, the supportive tissue beneath the stomach lining. They account for less than 1% (1 in 100) of cancers that start in the stomach. Treatment and outcome differs from gastric adenocarcinoma. For more information and support, visit Gist Cancer UK

How stomach cancer starts

This information is about stomach cancer (gastric adenocarcinoma).

Inflammation

Many stomach cancers begin with long-term inflammation of the stomach lining, known as gastritis. Causes include H. pylori infection, a diet high in salt or nitrites, smoking, certain autoimmune diseases, or combinations of these.

Chronic inflammation can damage the stomach lining. This can lead to:

• intestinal metaplasia, where stomach cells change and begin to resemble intestinal cells.
• atrophic gastritis, where the stomach lining may thin and lose function (atrophy).
• dysplasia, where some cells undergo pre-cancerous changes that can lead to cancer over time.

These changes take place over many years and are known as Correa’s cascade. Many people have no symptoms or only general symptoms like indigestion, while these changes take place.

Genetic mutations

About 40% (4 in 10) of stomach cancers are diffuse subtype. These may be because of inherited or acquired gene mutations, though in most cases the cause is unknown. Diffuse cancers grow by spreading through the stomach wall rather than forming a distinct tumour, making early detection more difficult.

The next page looks at the causes and risk factors for developing stomach cancer.