Marginal zone lymphomas are typically considered as two types:
- Extranodal marginal zone lymphoma of mucosa associated lymphoid tissues, also known as MALT lymphoma
- Nodal marginal zone lymphoma
Extranodal marginal zone lymphoma
MALT lymphoma is an uncommon form of B-cell lymphoma, but is the most common form of lymphoma that involves the stomach. Slightly more women are affected.
MALT lymphoma most commonly arises in the gastrointestinal tract (50% of cases), and 85% of these cases begin in the stomach. Other sites include:
- Salivary glands
- Head and Neck
- Ocular Adnexa ("Orbital MALT")
Most cases arise in the setting of a chronic inflammatory condition. For instance, gastric MALT arises in the setting of helicobacter pylori infection; orbital MALT often arises in patients with Sjogren syndrome; thyroid MALT often occurs in the setting of autoimmune (Hashimoto's Thyroiditis).
The course of disease is usually indolent and disseminate late; gastric MALT is particularly indolent.
Clinical symptoms depend on the site of disease. Systemic symptoms or other findings are rare. Gastric MALT presents with symptoms similar to dyspepsia. Intestinal MALT presents with obstructive symptoms or bleeding. Orbital, thyroid or skin MALT presents with a mass; diplopia may occur with orbital MALT.
Investigations are aimed at detecting distant disease.
The cell population in MALT lymphoma is mixed. Most cells are small and resemble centrocytes and normal lymphocytes; there are scattered centroblasts and immunoblasts. Lymphoid cells often infiltrate the epithelial layer of the involved tissue. No specific immunohistochemical markers exist; CD20, CD79a, CD21 and CD35 are usually positive but are also positive in many other lymphomas. A variety of genetic mutations have been identified; translocations involving chromosome 14 and 11 are common.
Nodal Marginal Zone Lymphoma
Nodal Marginal Zone Lymphoma is diagnosed when the lymphoma is not associated with an extranodal site. It has similar tumour features to the MALT type; clinical features are usually involve non-painful enlargement of lymph nodes. It is important to screen for common MALT lymphoma as this is present about a third of suspected nodal marginal zone lymphomas. It has a less favourable prognosis than MALT lymphoma.
Splenic Marginal Zone Lymphoma
An uncommon form of marginal zone lymphoma that primarily involves the spleen and splenic hilar nodes. Patients present with splenomegaly and usually thromobcytopenia. Bone marrow is frequently involved, but the course is indolent. There is a mixed population of cells, often with an enlarged marginal zone surrounding follicle-like structures. Immunohistochemistry is useful in excluding other lymphoma types (eg. mantle cell lymphoma). Despite the more extensive presentation of the disease, long term survival is common.
The Ann Arbor staging system is currently used for lymphoma.
|I||Involvement of one lymph node site|
|IE||Involvement of a single extra-lymphatic site|
|II||Involvement of two or more lymph node sites, on one side of the diaphragm|
|IIE||Involvement of a single extra-lymphatic site and one or more lymph node groups, on one side of the diaphragm|
|III||Involvement of lymph nodes on both sides of the diaphragm|
|IIIE||Involvement of a single extra-lymphatic site, with nodes on both sides of the diaphragm|
|IIIS||Involvement of the spleen with nodes on both sides of the diaphragm|
|IIIE+S||Involvement of the spleen, a single extra-lymphatic site, with nodes on both sides of the diaphragm|