Almost all stomach cancers are adenocarcinomas. But some rarer types may be more aggressive, affecting your treatment options and outlook.

Stomach cancer (or gastric cancer) happens when cancerous cells grow in your stomach.

Your stomach is made up of several parts where stomach cancer may appear:

  • Cardia: The cardia is where your esophagus, the food pipe, empties out into your stomach.
  • Fundus: The fundus is the bulb-shaped area at the top of your stomach near the cardia.
  • Body: The body is the largest part of your stomach that expands when you eat.
  • Pylorus: The pylorus is a funnel-shaped area that brings food from your stomach into the start of your small intestine.

Read on to learn more about the types of stomach cancer, when to contact a doctor, and how doctors diagnose the different types.

Adenocarcinomas of the stomach (aka gastric adenocarcinomas) happen when mucus-producing cells in your stomach become cancerous and grow rapidly. It’s the most commonly diagnosed type of stomach cancer. According to the American Cancer Society, adenocarcinomas account for 90% to 95% of all stomach cancers.

Adenocarcinomas fall into three categories:

  • Proximal: Proximal cancer appears in areas near the beginning of your stomach, such as in the cardia.
  • Distal: Distal cancer appears lower in your stomach, such as in the body or pylorus.
  • Diffuse: Diffuse cancer appears in multiple areas of your stomach.

Doctors usually treat gastric adenocarcinomas with chemotherapy or radiation therapy to kill cancer cells. Surgery may also be required to remove affected parts of your stomach to stop the cancer from spreading.

Hereditary diffuse gastric cancer

Hereditary diffuse gastric cancer (HDGC) is a rare type of stomach adenocarcinoma.

HDGC occurs when you inherit a mutated gene from one of your parents that puts you at high risk of stomach cancer and, in some cases, breast cancer.

Gastrointestinal stromal tumors (GISTs) occur when a special type of nerve cell in your stomach lining and walls becomes cancerous.

GISTs can develop anywhere in your digestive tract but are common in your stomach, especially in people older than 60 years old.

Small GISTs may simply need monitoring. When they grow bigger than 2 centimeters, doctors can surgically remove them.

Other possible treatments for GISTs are tyrosine kinase inhibitors that act on tyrosine kinase receptors. These receptors are involved in cell growth, helping to stop the growth of cancerous cells.

Gastrointestinal neuroendocrine tumors — aka neuroendocrine neoplasms (NENs) — occur when cancerous cells form in neuroendocrine cells. Neuroendocrine cells produce hormones that help with digestion and muscle contractions that move food through your digestive tract.

When you have gastrointestinal NENs, neuroendocrine cells can also produce too much or too little of the hormones they usually produce.

This can cause changes in your digestion that can result in symptoms like abdominal pain, diarrhea, constipation, or stomach paralysis (gastroparesis).

Gastric lymphoma is a rare type of stomach cancer that occurs when your immune system mistakenly attacks lymphatic tissues in your stomach, causing the growth of cancer cells. Lymphatic tissue is made up of immune cells called lymphocytes.

People with a history of Heliobacter pylori bacterial infections are at a higher risk of gastric lymphomas.

Most people have either of two types of gastric lymphoma:

Doctors often treat gastric lymphomas with chemotherapy or radiation therapy. Antibiotics may also help treat severe or recurring H. pylori infections.

Sarcomatoid carcinoma of the stomach is a very rare stomach cancer type. With this type, distal tumors can grow and spread very quickly and affect nearby lymph nodes in your stomach.

Early diagnosis is important to ensure treatment for this type of stomach cancer is started before the tumors become too big to remove or to treat safely.

What is the most aggressive type of stomach cancer?

Diffuse types of stomach cancer that happen in multiple areas of your stomach are the most aggressive types.

HDGC and diffuse adenocarcinomas in your stomach are typically very aggressive and need treatment as early as possible to prevent them from spreading.

Contact a doctor if you start to regularly experience common symptoms of stomach cancer, including:

Get immediate medical help if you experience severe symptoms that might indicate stomach cancer, including:

  • blood in your poop
  • lumps on your abdomen
  • nausea
  • vomiting
  • losing weight for no obvious reason
  • abnormal swelling or fluid buildup in your stomach area
  • yellowing of your eyes and skin (jaundice)

A doctor might use any of the following tests to diagnose the type of stomach cancer you have:

  • CT scan: A CT scan looks for the presence of cancerous tumors using detailed images of your stomach.
  • PET scan: A PET scan looks at your body while injected glucose lights up tumors when it passes through them.
  • Upper endoscopy: An upper endoscopy uses a thin, lighted tube with a camera on the end to look inside your esophagus, stomach, and duodenum (where the small intestine connects to the stomach).
  • Biopsy: A biopsy is a procedure that removes a sample of tissue to undergo analysis in a lab.
  • Tumor marker tests: Tumor marker tests measure substances in your blood, urine, or cells like chromogranin A.
  • MRI: MRI is imaging that uses a powerful magnet and radio waves to create detailed images of the inside of your body.
  • Metaiodobenzylguanidine (MIBG) scan: An MIBG scan uses an injected radioactive substance that causes cancerous tumors to light up on the scan images.

Several types of stomach cancer can develop in different parts of your stomach or affect different tissues. Most are adenocarcinomas, but rarer types like GISTs, NENs, and lymphomas may require different treatments or affect your outlook.

Contact a doctor if you suspect that you have stomach cancer. Early diagnosis and treatment can help stop tumors from spreading or from becoming hard to treat.