by Jason Wasserman MD PhD FRCPC and Aleksandra Paliga MD FRCPC
May 20, 2023
Extranodal marginal zone lymphoma (EMZL) of mucosal-associated lymphoid tissue (MALT) is a type of cancer made up of immune cells called B cells. It is considered an indolent type of cancer because the tumour grows very slowly and the cells are unlikely to spread to other parts of the body. Another name for this type of cancer is MALT lymphoma.
Extranodal marginal zone lymphoma can start almost anywhere in the body, however, the most commonly affected sites are the stomach, tissues around the eye, salivary glands, skin, lung, breast, thyroid gland, and thymus.
Despite their similar names, extranodal marginal zone lymphoma and marginal zone lymphoma are very different types of cancer. Most importantly, extranodal marginal zone lymphoma is considered an indolent disease that rarely spreads beyond the organ where it started. In contrast, nodal marginal zone lymphoma is a more aggressive disease that can spread to multiple lymph nodes in the same area of the body.
Extranodal marginal zone lymphoma is caused by prolonged inflammation in an area of the body, typically as a result of infection, an autoimmune condition, or other unknown factors. For example, extranodal marginal zone lymphoma in the stomach is commonly associated with Helicobacter pylori infection and treatment involves eradication of the bacteria from the stomach with antibiotics. In contrast, extranodal marginal zone lymphoma of the salivary gland and thyroid gland are associated with autoimmune conditions that affect these organs, specifically Sjogren’s disease and Hashimoto’s thyroiditis.
The symptoms of extranodal marginal zone lymphoma depend on the area of the body involved, however, many patients with extranodal marginal zone lymphoma have no symptoms and the tumour is discovered incidentally (by accident) when tests such as a CT scan or MRI are performed for other reasons. When the digestive system is involved, symptoms may include abdominal pain, bloating, and weight loss. In more superficial sites, extranodal marginal zone lymphoma may result in a noticeable, slow-growing mass.
Yes, it is possible for the tumour cells in extranodal marginal zone lymphoma to spread outside of the organ where the disease started to nearby lymph nodes or other organs. However, for most people with extranodal marginal zone lymphoma, the disease will remain isolated to the organ when the tumour started.
The diagnosis of extranodal marginal zone lymphoma can only be made after a sample of the tumour is removed in a procedure called a biopsy and the tissue is examined under a microscope by a pathologist.
When examined under the microscope, extranodal marginal zone lymphoma is made up of small immune cells called B cells. Pathologists often describe the tumour cells as atypical because they look different than normal, healthy B cells. The cells in extranodal marginal zone lymphoma may also be described as centrocyte-like or monocytoid because they resemble immune cells called centrocytes and monocytes. The tumour cells in extranodal marginal zone lymphoma grow in large groups called sheets which damage the surrounding tissue. The pattern is often described as architectural distortion or effacement. The tumour cells may also surround normal immune structures called follicles.
A test called immunohistochemistry may be performed to confirm the diagnosis. This test allows your pathologist to see proteins being made by the tumour cells. When this test is performed, the tumour called in extranodal marginal zone lymphoma are typically positive for CD20, CD79a, and PAX-5 and negative for CD5, CD10, BCL6, CD23, cyclin D1 and SOX-11.