Extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma) is a rare, slow-growing type of blood cancer that develops outside the lymph nodes, most commonly in the stomach, lungs, or areas around the eyes. This condition often remains localized and can sometimes be linked to chronic infections or autoimmune conditions, making it unique among lymphomas in both its behavior and treatment approach.
What Is MALT Lymphoma?
MALT lymphoma belongs to a group of cancers called marginal zone lymphomas. These cancers develop from a specific type of white blood cell known as B lymphocytes, or B cells, which are part of the body’s immune system and help fight infections. The term “MALT” stands for mucosa-associated lymphoid tissue, which refers to the moist inner lining found in various organs and body cavities, including the digestive tract, lungs, and areas around the eyes.[1]
This lymphoma is called “extranodal” because it starts in body organs rather than in the lymph nodes themselves. The word extranodal simply means “outside the lymph nodes.” Unlike many other lymphomas that begin in lymph nodes and then spread to organs, MALT lymphoma typically does the opposite—it starts in organs and may or may not involve lymph nodes later.[3]
MALT lymphoma is considered an indolent lymphoma, meaning it grows very slowly compared to more aggressive forms of cancer. Many people with this condition may not experience symptoms for a long time, and some are diagnosed accidentally during medical tests for unrelated health issues. The slow-growing nature of MALT lymphoma often allows for careful monitoring and targeted treatment approaches.[4]
How Common Is This Condition?
MALT lymphoma is relatively uncommon. It accounts for approximately 7 to 8 percent of all B-cell lymphomas and represents one of the less frequently diagnosed types of non-Hodgkin lymphoma.[1] The condition typically affects older adults, with the median age at diagnosis being around 60 years.[1]
The disease shows a slight gender difference, appearing somewhat more frequently in men than in women.[5] Among all marginal zone lymphomas, MALT lymphoma is the most common subtype, making up about 50 to 70 percent of marginal zone lymphoma cases.[14]
When we look at where MALT lymphoma occurs in the body, the stomach is the most frequently affected site, accounting for more than 30 percent of all MALT lymphoma cases. This stomach-based form is often called gastric MALT lymphoma. Other common locations include the tissue around the eyes (ocular adnexa), salivary glands, lungs, skin, thyroid gland, and breasts.[14]
The disease typically presents in a localized stage, meaning it stays confined to one area of the body. Most people are diagnosed when the lymphoma is at stage I or II. However, in some cases—ranging from 25 to 50 percent—the disease can be disseminated, meaning it has spread to multiple locations in the body at the time of diagnosis.[1]
What Causes MALT Lymphoma?
The development of MALT lymphoma is often linked to chronic inflammation caused by persistent infections or autoimmune conditions. Unlike many cancers where the cause remains unclear, MALT lymphoma has several well-documented triggers that can set the stage for cancer development.[1]
The most well-established connection is between gastric MALT lymphoma and infection with a bacterium called Helicobacter pylori, or H. pylori. This bacterium causes chronic stomach inflammation known as gastritis. About two-thirds of people with gastric MALT lymphoma have a history of H. pylori infection. The ongoing inflammation and immune response triggered by this bacterium can eventually lead to changes in B cells, causing them to become cancerous.[4]
Other bacterial and viral infections have also been associated with MALT lymphoma in different body locations. For example, infection with Chlamydophila psittaci (formerly called Chlamydia psittaci) has been linked to MALT lymphoma developing in the conjunctiva and tissue around the eyes. Borrelia burgdorferi, the bacterium that causes Lyme disease, has been associated with skin MALT lymphoma. Hepatitis C virus infection has been connected to both gastric and non-gastric MALT lymphoma.[4][14]
Autoimmune diseases also play a significant role in MALT lymphoma development. Autoimmune conditions occur when the body’s immune system mistakenly attacks its own tissues, leading to chronic inflammation. Sjögren’s syndrome, an autoimmune disease affecting the glands that produce tears and saliva, is strongly associated with MALT lymphoma of the salivary glands. Hashimoto’s thyroiditis, an autoimmune condition affecting the thyroid gland, is linked to thyroid MALT lymphoma.[5][8]
The underlying mechanism involves chronic antigenic stimulation—a process where the immune system is continuously activated by foreign substances (antigens) from infections or by the body’s own tissues in autoimmune conditions. This persistent immune activation creates an environment where B cells can undergo genetic changes, eventually becoming cancerous.[14]
Risk Factors for Developing MALT Lymphoma
Several factors can increase a person’s likelihood of developing MALT lymphoma. Understanding these risk factors helps identify individuals who may benefit from closer monitoring or preventive measures.[5]
Having a family history of lymphoma is a notable risk factor. People with close relatives who have had lymphoma may have a higher risk of developing MALT lymphoma themselves, suggesting that genetic factors play some role in susceptibility to this disease.[5]
Chronic bacterial infections represent another significant risk category. Persistent H. pylori infection in the stomach is the most prominent example, but other bacterial infections affecting different body sites can also increase risk. These infections create an environment of ongoing inflammation that can contribute to cancer development over time.[4]
Viral infections, particularly hepatitis C virus, have been identified as risk factors for various forms of MALT lymphoma. The virus can trigger immune system changes that may eventually lead to lymphoma development.[4]
Autoimmune disorders significantly elevate the risk of MALT lymphoma. Conditions such as Sjögren’s syndrome, Hashimoto’s thyroiditis, and systemic lupus erythematosus create chronic inflammation and immune system dysfunction that can predispose individuals to developing lymphoma in the affected tissues.[5][14]
Age is another important factor, as MALT lymphoma predominantly affects older adults, with most diagnoses occurring in people around 60 years of age or older.[1]
According to research from the International Lymphoma Epidemiology Consortium, other risk factors include having asthma, self-reported peptic ulcers, working as a metalworker, and regular use of permanent hair dye. These findings suggest that both genetic predisposition and environmental exposures contribute to MALT lymphoma risk.[19]
Symptoms and How They Affect Patients
The symptoms of MALT lymphoma vary greatly depending on where the cancer develops in the body. Because this lymphoma grows very slowly, many people may not experience any symptoms at all, especially in the early stages. Some individuals are diagnosed only when undergoing medical tests for other reasons.[8]
MALT lymphoma typically does not cause swollen lymph nodes, which distinguishes it from many other types of lymphoma. This is because the cancer develops outside the lymph nodes and may remain localized to the organ where it started.[8]
For gastric MALT lymphoma affecting the stomach, symptoms often resemble those of common digestive problems. People may experience persistent indigestion or heartburn that doesn’t improve with standard treatments. Belly pain is common, often described as a dull, uncomfortable feeling in the upper abdomen. Nausea and vomiting can occur, particularly after eating. Many people notice unintended weight loss, and some experience a persistent feeling of fullness even after eating small amounts of food. In some cases, gastrointestinal bleeding may occur, which could appear as blood in vomit or dark, tarry stools.[5][8]
When MALT lymphoma develops in the tissue around the eyes (ocular adnexa), it can cause visible changes. The eyelids may appear swollen or droopy. The eyes themselves might look red or irritated, similar to conjunctivitis. Some people notice swelling around the eye area. In more advanced cases, double vision can develop. These eye-related symptoms often develop gradually and may be mistaken for chronic eye infections or allergies.[5]
Lung involvement can lead to respiratory symptoms. A persistent cough that doesn’t go away is common. Some people experience shortness of breath, especially during physical activity. Chest pain may occur, and in rare cases, people might cough up blood. These symptoms can be mistaken for chronic respiratory conditions or infections.[5]
MALT lymphoma affecting the salivary glands typically causes painless swelling. The glands located in front of the ears, under the chin, or in the mouth may become noticeably enlarged. This swelling usually develops slowly and is often not accompanied by pain or tenderness.[5]
When the thyroid gland is involved, people may develop symptoms of hypothyroidism, including unusual fatigue, unexplained weight gain, dry skin, and increased sensitivity to cold temperatures. A visible or palpable lump may appear at the front of the neck where the thyroid gland is located.[5]
Skin MALT lymphoma can present as red, pink, or purple patches on the skin, or as raised lumps. These skin changes typically don’t cause pain or itching and may be mistaken for other skin conditions.[5]
Some people with MALT lymphoma experience general symptoms that aren’t specific to the location of the cancer. These can include fever without an obvious infection, night sweats that soak through bedclothes, and unexplained weight loss. However, these systemic symptoms are less common in MALT lymphoma compared to more aggressive types of lymphoma.[5]
Prevention Strategies
While it’s not possible to prevent all cases of MALT lymphoma, certain measures may help reduce the risk of developing this condition, particularly for gastric MALT lymphoma where the connection to H. pylori infection is well established.
The most effective preventive strategy for gastric MALT lymphoma is the detection and treatment of H. pylori infection. People with persistent stomach problems such as chronic indigestion, gastritis, or peptic ulcers should be tested for this bacterium. If H. pylori is detected, treatment with antibiotics can eliminate the infection and reduce the chronic inflammation that could eventually lead to lymphoma. This preventive approach is particularly important because eliminating H. pylori infection before lymphoma develops is far simpler than treating the cancer once it has formed.[4]
For people with autoimmune conditions such as Sjögren’s syndrome or Hashimoto’s thyroiditis, proper management of these underlying diseases may help reduce lymphoma risk. While having these conditions does increase the likelihood of developing MALT lymphoma, good disease control with appropriate medications and regular monitoring by healthcare providers can help minimize chronic inflammation.[5]
Regular health screenings and medical check-ups are valuable for early detection. People with known risk factors—such as family history of lymphoma, chronic infections, or autoimmune diseases—should maintain regular communication with their healthcare providers about any persistent or unusual symptoms.
Addressing modifiable risk factors identified in research may also be beneficial. This includes avoiding unnecessary long-term use of permanent hair dyes and following workplace safety guidelines if employed in occupations with higher lymphoma risk, such as metalworking.[19]
Maintaining overall immune system health through a balanced diet, regular exercise, adequate sleep, and stress management may contribute to general cancer prevention, though the specific impact on MALT lymphoma risk is not fully understood.
How MALT Lymphoma Develops: Understanding the Disease Process
MALT lymphoma develops through a complex process that begins with chronic stimulation of the immune system. Understanding how this cancer forms helps explain why it behaves differently from other lymphomas and why certain treatments can be so effective.
The process starts when normal B lymphocytes in the marginal zone—a specific area at the edge of lymphoid tissue where these immune cells reside—undergo genetic changes. These changes don’t happen randomly; they’re typically triggered by persistent inflammation caused by infections or autoimmune conditions. The marginal zone wraps around other areas of lymphoid tissue called mantle zones, and it’s in this marginal zone that the problematic B cells originate.[3][5]
In the case of gastric MALT lymphoma, the mechanism is well understood. H. pylori bacteria colonize the stomach lining, causing chronic inflammation. The body responds by recruiting immune cells, including B lymphocytes, to fight the infection. Over time, with continuous stimulation, some B cells acquire genetic mutations. These mutated cells begin to multiply uncontrollably, but unlike aggressive cancers, they do so slowly and in an organized manner.[14]
MALT lymphoma cells are morphologically heterogeneous, meaning they appear in various forms under the microscope. They typically look like small to medium-sized B cells with diverse appearances. What makes them cancerous is not their appearance alone, but their behavior: they multiply without normal growth controls and can accumulate in tissues.[1]
The cancer cells remain dependent on signals from their environment, at least initially. In gastric MALT lymphoma, the lymphoma cells often require continued stimulation from H. pylori bacteria or from immune system cells called T cells. This dependence explains why eliminating the bacterial infection can sometimes cause the lymphoma to disappear—without the stimulating signal, the cancer cells can no longer survive.[1]
As the disease progresses, lymphoma cells can become more independent. They may acquire additional genetic changes that allow them to grow without external stimulation. Specific genetic alterations have been identified in MALT lymphoma, including chromosomal translocations (where pieces of different chromosomes swap places) such as t(11;18), t(1;14), and others. These genetic changes affect pathways that control cell growth and survival, particularly the NFκB pathway, which plays a crucial role in inflammation and immune responses.[14]
MALT lymphoma tends to remain localized for long periods. The majority of patients present with stage I or II disease, meaning the cancer is confined to one site or a limited region. However, the disease can involve multiple extranodal sites, particularly in paired organs (such as both salivary glands) or within organ systems (such as different parts of the gastrointestinal tract). When it does spread, it often remains in mucosa-associated tissues rather than spreading to lymph nodes first, which is unusual compared to other lymphomas.[7]
Bone marrow involvement occurs in a minority of cases, and the frequency varies by the primary site of disease. Bone marrow involvement is less common in gastric MALT lymphoma but more frequent in lung and ocular adnexal MALT lymphoma.[7]
In some cases, MALT lymphoma can undergo transformation into a more aggressive form of lymphoma called diffuse large B-cell lymphoma (DLBCL). This transformation is associated with additional genetic changes, including mutations in the TP53 gene, loss of p16 protein, or rearrangements in the MYC gene. When transformation occurs, the cancer begins to grow more quickly and requires different, more intensive treatment approaches.[4][14]
