Gastric cancer, also known as stomach cancer, is a type of cancer that develops in the lining of the stomach. It occurs when cells in the stomach grow uncontrollably, forming a tumor. While gastric cancer can develop in any part of the stomach, it most commonly originates in the innermost layer called the mucosa. Over time, it can invade deeper layers of the stomach wall and spread to other parts of the body, including the esophagus, small intestine, lymph nodes, liver, and lungs.

The exact causes of gastric cancer are not fully understood, but several risk factors have been identified. Infection with Helicobacter pylori (H. pylori) bacteria is a major contributor, as it can lead to chronic inflammation and ulcers, increasing the risk of cancer development. Other risk factors include a diet high in salty and smoked foods, low intake of fruits and vegetables, smoking, excessive alcohol consumption, obesity, family history of gastric cancer, and certain genetic mutations. Gastric cancer is more common in older adults, with men being at higher risk than women.

Symptoms of gastric cancer often go unnoticed in the early stages, making it challenging to detect. Initial signs may include indigestion, bloating, mild nausea, and loss of appetite. As the disease progresses, more severe symptoms such as unexplained weight loss, difficulty swallowing, persistent abdominal pain, vomiting, and blood in stool or vomit may occur.

Diagnosis involves various tests, including endoscopy, where a flexible tube with a camera is used to examine the stomach, and biopsies to analyze tissue samples. Imaging tests like CT scans and X-rays may also help assess the extent of the disease.