Lymphomas are malignant neoplasms of lymphoid tissue and broadly classified into either Hodgkins lymphoma or non-Hodgkins lymphomas, though in the gastrointestinal system, the vast majority of neoplasms are non-Hodgkins. Most lymphomas arise in lymph nodes but a lymphoma can also arise in extranodal sites, such as the gastrointestinal tract. Lymphomas of the gastrointestinal tract can be primary or secondary. Of the primary GI lymphomas, some are unique, occurring only in the GI tract, while others represent lymphomas that correspond in type with those found in lymph nodes. GI lymphomas are the most common extranodal lymphomas. There are geographic differences in the incidence of GI lymphoma and in their location within the GI tract. For example, the stomach is the most common site of GI lymphoma in the West, while in the Middle East, most lymphomas occur in the small bowel. Mucosa-associated lymphoid tissue lymphoma is the most common type of primary GI lymphoma in Canada.
Immunoproliferative small intestinal disease occurs in young adults in poor socioeconomic conditions. It is common in the Middle East, where it is known as Mediterranean lymphoma. Usually, this disease involves the duodenum and proximal jejunum and is associated with abnormal IgA secretion. This lymphoma may also respond to antibiotics.
The liver is also affected by several gastrointestinal neoplasms. The most important of these is hepatocellular carcinoma, and other neoplasms include hepatic adenomas, hemangioma, hepatoblastoma, intrahepatic cholangiocarcinoma, and angiosarcoma. The most common etiology of malignant liver disease, however, is metastatic disease.