Mucosa-associated lymphoid tissue (MALT) lymphoma is a distinct form of non-Hodgkin lymphoma that develops from B-lymphocytes in the immune system. This type of cancer is generally characterized as a slow-growing or low-grade malignancy. MALT lymphoma typically arises in organs outside of the lymph nodes, and in a majority of cases, it remains localized to the site of origin for an extended period. Compared to many other lymphomas, this localized nature and slow growth rate contribute to a generally favorable prognosis for affected patients.
Understanding Mucosa-Associated Lymphoid Tissue
The “MALT” in MALT lymphoma refers to Mucosa-Associated Lymphoid Tissue, which is a diffuse collection of immune cells found throughout the body’s mucosal linings. These linings cover organs that interface with the outside world, such as the digestive tract, lungs, eyes, and salivary glands.
The primary role of this tissue is to serve as a first line of defense, trapping foreign particles and pathogens that enter the body through mucosal surfaces. MALT consists of specialized immune cells, including B-cells and T-cells, that constantly sample antigens to initiate an immune response. When a foreign substance is detected, the B-cells within the MALT begin to proliferate and differentiate to mount a local defense.
MALT lymphoma originates when this normal immune response goes awry, specifically affecting the B-cells in the marginal zone of the lymphoid tissue. The cancer develops after a prolonged period of chronic inflammation, where persistent irritation or infection continuously stimulates the B-cells. Over time, this chronic stimulation leads to uncontrolled growth and proliferation of the B-cells, resulting in the formation of a localized tumor.
Known Triggers and Associated Infections
A defining characteristic of MALT lymphoma is its strong association with chronic bacterial infection. The most well-known example is the link between the bacterium Helicobacter pylori and gastric MALT lymphoma, which accounts for the majority of cases. This bacterium infects the stomach lining, causing chronic gastritis that continually recruits and activates immune cells.
The association is so strong that eradication of the infection often leads to the regression of the lymphoma. This responsiveness highlights the continuous dependence of the cancerous B-cells on the infectious trigger. The underlying infection is not always H. pylori, as other bacteria are linked to MALT lymphoma in non-gastric sites.
For example, Chlamydia psittaci has been connected to MALT lymphoma that develops around the eye, known as ocular adnexal MALT lymphoma. Similarly, the spirochete Borrelia burgdorferi, the agent responsible for Lyme disease, is associated with MALT lymphoma that presents on the skin, called cutaneous MALT lymphoma.
Identifying and Classifying MALT Lymphoma
Symptoms of MALT lymphoma are often subtle and non-specific, largely depending on the organ where the tumor is located. For gastric MALT lymphoma, which is the most common form, patients may experience symptoms related to the stomach, such as abdominal pain, persistent indigestion, or nausea. MALT lymphoma in other areas might cause a lump in the neck if it affects the thyroid or salivary glands, or vision changes if it is near the eye.
A tissue sample, or biopsy, is mandatory for a definitive diagnosis. For suspected gastric involvement, this typically involves an endoscopic biopsy, where a small piece of the stomach lining is removed for microscopic analysis. Histological examination confirms the presence of the abnormal B-cells and verifies the MALT lymphoma subtype.
Once the disease is confirmed, it is classified using staging systems, such as the Ann Arbor or Lugano classifications, to determine the extent of its spread. These systems help define how localized the cancer is, which is particularly important for MALT lymphoma since it often remains confined to the site of origin. Staging typically involves imaging tests, such as CT scans and endoscopic ultrasonography, to assess local infiltration and distant spread to other organs or lymph nodes.
Treatment Approaches Based on Location and Stage
The highly localized nature and infectious association of MALT lymphoma lead to a unique, tiered treatment strategy. For early-stage gastric MALT lymphoma that tests positive for H. pylori, the initial approach is often to use a combination of antibiotics to eradicate the bacteria. Eradication of the infectious trigger alone can lead to complete remission of the lymphoma in a significant percentage of patients.
If the lymphoma does not respond to antibiotics, is H. pylori-negative, or is in a localized non-gastric site, the next step is typically localized radiation therapy. Low-dose radiation directed precisely at the tumor site is highly effective and can achieve excellent long-term local control with minimal side effects. This organ-preserving approach is preferred for localized disease that requires more than just antibiotic treatment.
For advanced or disseminated disease, or for tumors that resist local therapies, systemic treatments are employed. These options include chemotherapy or targeted agents, such as the monoclonal antibody Rituximab, which targets the cancerous B-cells.