You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is Gastric lymphoma and explain in detail?
Primary gastric lymphoma (lymphoma that originates in the stomach itself) is an uncommon condition, accounting for less than 15% of gastric malignancies and about 2% of all lymphomas.  However, the stomach is a very common extranodal site for lymphomas (lymphomas originate elsewhere and metastasise to the stomach). It is also the most common source of lymphomas in the gastrointestinal tract.

Signs and symptoms
Symptoms include epigastric pain, early satiety, fatigue and weight loss. Most people affected by primary gastric lymphoma are over 60 years old.

Risk factors
Risk factors for gastric lymphoma include the following:

Helicobacter pylori
Long-term immunosuppressant drug therapy
HIV infection

Pathophysiology
The majority of gastric lymphomas are non-Hodgkins lymphoma of B-cell origin.  These tumors may range from well-differentiated, superficial involvements (MALT) to high-grade, large-cell lymphomas. Sometimes, its hard to differentiate poorly differentiated high grade B-cell gastric lymphoma from gastric adenocarcinoma clinically or radiologically, yet histopathology with immunohistochemistry is recommended to stain specific markers on the malignant cell that favor the diagnosis of lymphoma. Immunohistochemistry stains specific clusters of differentiation that are present on B-cells like CD20. Cytokeratin is also a surface marker that is presented on epithelial cells, is stained histochemically and favors the diagnosis of epithelial tumors like adenocarcinoma.
Differentiating poor gastric lymphoma from adenocarcinoma is essential because the prognosis and modalities of treatment differ significantly.
Other lymphomas involving the stomach include mantle cell lymphoma and T-cell lymphomas which may be associated with enteropathy; the latter usually occur in the small bowel but have been reported in the stomach.

Diagnosis
These lymphomas are difficult to differentiate from gastric adenocarcinoma