What Is Stomach Cancer?
A plain-language overview of stomach (gastric) cancer, where it starts in the stomach, and the main types, based on National Cancer Institute resources.
Source: National Cancer Institute · Verified 2026-07-02
The 30-second version
Stomach cancer, also called gastric cancer, starts in the cells lining the stomach. The stomach is a digestive organ in the upper left abdomen. Nearly all stomach cancers are adenocarcinomas, which begin in the mucus-making cells of the stomach lining. Doctors also describe stomach cancer by where in the stomach it forms.
Key takeaways
- Stomach (gastric) cancer starts in the cells lining the stomach.
- The stomach is part of the digestive tract and helps break down food.
- Nearly all stomach cancers are adenocarcinomas, which begin in the mucus-producing cells of the innermost lining.
- Adenocarcinoma is grouped as gastric cardia cancer (near the esophagus) or non-cardia cancer (elsewhere in the stomach).
- It can also be described as intestinal or diffuse, based on how the cells look under a microscope.
- Other, rarer types include neuroendocrine tumors, GIST, and primary gastric lymphoma.
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The full explanation.
The simple version
Stomach cancer, also called gastric cancer, is cancer that starts in the cells lining the stomach. The stomach is an organ on the left side of the upper abdomen that digests food.
The stomach is part of the digestive tract. This is a series of hollow, muscular organs joined in a long, twisting tube that runs from the mouth to the anus. The digestive tract processes the nutrients in the food you eat and helps pass waste out of the body.
In short: stomach cancer begins in the cells that line the stomach.
How the stomach works
Your stomach is one stop along the digestive tract:
- Food moves from the throat to the stomach through a tube called the esophagus.
- After food enters the stomach, stomach muscles mix it with digestive juices to break it down.
- The partly digested food then passes into the small intestine, and later into the large intestine.
- The end of the large intestine, called the rectum, stores waste until it leaves the body.
The main type: adenocarcinoma
Nearly all stomach cancers are adenocarcinomas. Adenocarcinoma of the stomach begins in the mucus-producing cells in the innermost lining of the stomach.
Doctors group adenocarcinoma of the stomach by where it forms:
- Gastric cardia cancer begins in the top inch of the stomach, just below where it meets the esophagus.
- Non-cardia gastric cancer begins in all other parts of the stomach.
Adenocarcinoma can also be described by how the cells look under a microscope:
- Intestinal adenocarcinomas are well differentiated, meaning the cancer cells look similar to normal cells.
- Diffuse adenocarcinomas are poorly differentiated, meaning the cancer cells look different from normal cells. Diffuse adenocarcinomas tend to grow and spread more quickly and can be harder to treat.
In short: most stomach cancers are adenocarcinomas that start in the stomach's inner lining.
Other types of stomach cancer
Some less common cancers can also start in the stomach:
- Gastroesophageal junction (GEJ) adenocarcinoma forms where the esophagus meets the top of the stomach. It may be treated like stomach cancer or like esophageal cancer.
- Gastrointestinal neuroendocrine tumors begin in neuroendocrine cells, which act like both nerve and hormone-making cells lining the gastrointestinal tract.
- Gastrointestinal stromal tumors (GIST) begin in nerve cells in the wall of the stomach and other digestive organs. GIST is a type of soft tissue sarcoma.
- Primary gastric lymphoma is a type of non-Hodgkin lymphoma that forms in the stomach.
Rarely, other types such as squamous cell carcinoma, small cell carcinoma, and leiomyosarcoma can also begin in the stomach.
In short: adenocarcinoma is by far the most common type, but several rarer types exist.
Everyone's situation is different. Your healthcare team is the best source of information about your own health and any next steps.
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Animated lessons are in production. Here’s the planned video slate for this topic — each one will be based on the same NCI-sourced explanation you’re reading.
What Is Stomach Cancer: the quick overview
A one-breath explanation you can watch before an appointment.
Coming soonWhat Is Stomach Cancer, explained simply
The core ideas with friendly animation and plain language.
Coming soonUnderstanding what is stomach cancer — full lesson
A deeper walkthrough covering the key takeaways and common questions.
Coming soonVideo transcript▾
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Suggested animation storyboard▾
- 1Open on a calm title card: "What Is Stomach Cancer?" with the Cancer Explained mark.
- 2Narrator reads the 30-second summary while a soft animated diagram builds on screen: "Stomach cancer, also called gastric cancer, starts in the cells lining the stomach. The stomach is a digestive organ in the upper left abdomen. Nearly all stomach cancers are adenocarcinomas, which begin in the mucus-making cells of the stomach lining. Doctors also describe stomach cancer by where in the stomach it forms."
- 3Scene 2: illustrate the idea — "Stomach (gastric) cancer starts in the cells lining the stomach."
- 4Scene 3: illustrate the idea — "The stomach is part of the digestive tract and helps break down food."
- 5Scene 4: illustrate the idea — "Nearly all stomach cancers are adenocarcinomas, which begin in the mucus-producing cells of the innermost lining."
- 6Close on a reminder card: this is educational only; talk with your healthcare team, and a link to the NCI source.
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Quick knowledge check
According to this article, where does stomach cancer start?
Frequently asked questions
▸What is stomach cancer?
Stomach cancer, also called gastric cancer, is cancer that starts in the cells lining the stomach. The stomach is an organ on the left side of the upper abdomen that digests food. It is part of the digestive tract, a long, twisting tube of hollow, muscular organs that runs from the mouth to the anus.
▸What does the stomach do?
Food moves from the throat to the stomach through a tube called the esophagus. After food enters the stomach, stomach muscles mix it with digestive juices to break it down. The partly digested food then passes into the small intestine and later the large intestine.
▸What is the most common type of stomach cancer?
Nearly all stomach cancers are adenocarcinomas. Adenocarcinoma of the stomach begins in the mucus-producing cells in the innermost lining of the stomach.
▸How is adenocarcinoma of the stomach classified?
It is divided into two main classes based on where it forms. Gastric cardia cancer begins in the top inch of the stomach, just below where it meets the esophagus. Non-cardia gastric cancer begins in all other parts of the stomach. It can also be described as intestinal or diffuse, depending on how the cells look under a microscope.
▸Are there other types of stomach cancer besides adenocarcinoma?
Yes, but they are less common. Other types include gastrointestinal neuroendocrine tumors, gastrointestinal stromal tumors (GIST), and primary gastric lymphoma. Rarely, other types such as squamous cell carcinoma, small cell carcinoma, and leiomyosarcoma can also begin in the stomach.
▸What is gastroesophageal junction (GEJ) adenocarcinoma?
Gastroesophageal junction adenocarcinoma is a cancer that forms in the area where the esophagus meets the top of the stomach. It may be treated similarly to stomach cancer or to esophageal cancer.
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Questions to ask your healthcare team
Consider bringing these questions to your next appointment.
- What type of stomach cancer do I have?
- Where in my stomach did the cancer start?
- What tests do I need to learn more about my cancer?
- What do the terms in my pathology report mean?
- Where can I find reliable information and support?
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