Marginal Zone Lymphoma: Subtypes, Triggers, and Staging

Marginal zone lymphoma is a slow-growing cancer of B cells, a type of white blood cell, that accounts for roughly 7% of all non-Hodgkin lymphomas. It comes in three distinct subtypes defined by where in the body the disease starts, and this geography shapes everything from its likely cause to how it is treated. Because it tends to behave indolently, many people live years or even decades after diagnosis, but the disease is far from uniform, and some cases demand prompt treatment while others can be safely watched.

The Three Subtypes and Why They Matter

Marginal zone lymphoma (MZL) is not one disease but three, each named for the tissue it arises in. Extranodal MZL of mucosa-associated lymphoid tissue, usually called MALT lymphoma, is the most common and develops in organs that are not normally part of the immune system, such as the stomach, lungs, eyes, thyroid, or skin. Splenic MZL starts in the spleen and often shows up as a markedly enlarged spleen along with abnormal lymphocytes circulating in the blood. Nodal MZL, the rarest of the three, originates in lymph nodes and can be tricky to distinguish from other small B-cell lymphomas like follicular lymphoma.

All three subtypes share some genetic ground. Gains of extra copies of chromosomes 3 and 18, deletions in a region of chromosome 6, and overactivation of the NF-κB signaling pathway are common threads. Yet each subtype also carries its own molecular fingerprint. Splenic MZL frequently harbors mutations in KLF2 and NOTCH2, while MALT lymphomas at different body sites tend to have mutations in NF-κB pathway genes like TNFAIP3, and pulmonary and nodal MZL more often show changes in chromatin-remodeling genes such as KMT2D.¹ These differences are not just academic. They help pathologists confirm which subtype a patient has and, increasingly, guide treatment decisions.

Infections That Trigger Marginal Zone Lymphoma

One of the most remarkable things about MZL is that in many cases, a chronic infection is the apparent spark. The best-understood example is gastric MALT lymphoma and the stomach bacterium Helicobacter pylori. The bacterium does not directly transform B cells into cancer. Instead, it sets off a prolonged immune response: T cells are stimulated, inflammatory signaling ramps up, and B cells in the stomach lining begin dividing in response to the ongoing antigenic stimulation. Over time, that persistent drive can push a clone of B cells toward malignancy.²

This connection has a dramatic clinical payoff. In early-stage gastric MALT lymphoma that tests positive for H. pylori, simply eradicating the bacterium with standard antibiotic therapy can make the lymphoma regress, sometimes completely.³ At later stages, though, the tumor may acquire additional genetic abnormalities that make it independent of the bacterium, at which point antibiotics alone no longer work.⁴

The infection-lymphoma link extends beyond the stomach. MALT lymphomas at other body sites have been associated with other pathogens: Borrelia burgdorferi (the Lyme disease bacterium) with skin MALT lymphoma, Chlamydia psittaci with ocular adnexal MALT lymphoma, Campylobacter jejuni with small-intestinal MALT lymphoma, and hepatitis C virus with both MALT lymphoma and splenic MZL.⁵ A common theme unites these associations: chronic antigenic stimulation from infection drives immune responses that eventually tip from protective to pathological.

The Hepatitis C Connection With Splenic MZL

Splenic MZL deserves special mention because its relationship with hepatitis C virus (HCV) has direct treatment implications. In a landmark study, patients with splenic lymphoma who were also infected with HCV received antiviral therapy. Among nine HCV-positive patients treated with interferon alfa, seven achieved complete remission of their lymphoma once the virus became undetectable in the blood. The remaining two responded after ribavirin was added. Meanwhile, none of the HCV-negative patients responded to the same interferon treatment, reinforcing that the antiviral effect, not any direct anti-cancer property of interferon, was responsible.⁶

With the arrival of modern direct-acting antiviral drugs that cure HCV without interferon, the same principle has held up. A case of HCV-related splenic MZL treated with an interferon-free antiviral regimen achieved rapid viral clearance and, with it, cure of the lymphoma, with a clear statistical correlation between viral decline and lymphocyte improvement.⁷ For patients with HCV-associated splenic MZL, treating the virus is treating the lymphoma.

Autoimmune Disease as a Risk Factor

Chronic infections are not the only source of prolonged immune stimulation. Autoimmune disorders, where the immune system attacks the body’s own tissues, also raise the risk of MZL. A large pooled analysis found that Sjögren syndrome, a condition that primarily affects the salivary glands and tear ducts, was tied to a strikingly elevated risk of parotid gland marginal zone lymphoma. Systemic lupus erythematosus carried a roughly two-and-a-half-fold increase in overall non-Hodgkin lymphoma risk, with marginal zone lymphoma among the subtypes affected.⁸

The biology here mirrors the infection story. Autoimmune diseases keep the immune system in a state of constant activation, and the tissue sites that bear the brunt of that activation are the same sites where MZL tends to emerge. Someone with Sjögren syndrome has chronically inflamed salivary glands, and that is precisely where their lymphoma risk is highest. Recognizing this connection matters because it means patients with certain autoimmune conditions should be monitored for lymphoma, and clinicians should keep MZL on their differential when evaluating unexplained masses in those patients.

How MZL Is Diagnosed

Diagnosing MZL requires a tissue biopsy, and it can be one of the more difficult lymphomas to pin down. There is no single marker that lights up and says “marginal zone lymphoma.” Instead, pathologists use a combination of what the cells look like under the microscope and which surface proteins they express. MZL cells typically express the B-cell markers CD19 and CD20 but lack the hallmark proteins of other small B-cell lymphomas. They are generally negative for CD10 and CD5, which helps distinguish them from follicular lymphoma and mantle cell lymphoma, respectively.⁹

Nodal MZL can be especially difficult to separate from follicular lymphoma because both present as small B cells growing in lymph nodes. Research has found that a panel of three immunohistochemical stains, CD23, CD10, and LMO2, correctly classified about 94% of cases in one study. CD23 was positive in nearly two-thirds of nodal MZL cases but almost never in follicular lymphoma, making it one of the more useful single markers for this distinction.¹⁰

Imaging and Staging

Standard lymphoma staging uses PET/CT scans with the radiotracer FDG, and for years, guidelines classified extranodal MZL as a disease that does not reliably show up on FDG-PET. A recent study of 152 patients challenges that assumption. FDG avidity was detected in about 80% of extranodal MZL sites, with particularly high rates in salivary gland, bone, lung, and ocular adnexal locations. Skin was the main exception, rarely lighting up on PET.¹¹ Another study found that PET/CT had 96% sensitivity for detecting MZL lesions compared with 76% for conventional CT, and in nearly half of patients both tests were available at diagnosis, PET found more involved sites than CT alone.¹²

An emerging approach targets CXCR4, a receptor found on MZL cells, with a different radiotracer called 68Ga-pentixafor. In one study, CXCR4-directed PET correctly identified every patient who had active MZL and outperformed conventional staging. Adding this scan changed the stage assignment in almost half of patients and altered treatment plans in about a third.¹³ CXCR4 PET is not yet widely available, but it highlights the direction imaging is heading for cancers that do not always cooperate with standard FDG scans.

Treatment When the Disease Is Localized

Because MZL often stays in one area for a long time, many patients do not need aggressive treatment right away. For gastric MALT lymphoma linked to H. pylori, antibiotic eradication therapy is the first-line approach, as discussed above. For localized MALT lymphoma at other sites, options include surgery, radiation therapy, or simply watching and waiting.

Lung MALT lymphoma (also called BALT lymphoma) illustrates the watch-and-wait philosophy well. In a study of 123 patients, nearly half were managed with active surveillance alone, meaning regular check-ups without any treatment. At six years, overall survival was 93% across all management strategies. Surgical resection had slightly better event-free survival than observation or systemic therapy, but all groups did well. Larger lesions and low platelet counts were the main factors linked to shorter event-free survival.¹⁴ The key takeaway is that a diagnosis of MZL does not automatically mean starting treatment. For many people, careful monitoring is a safe and effective strategy.

Systemic Treatment Options

When MZL is more widespread, or when localized disease progresses and requires systemic therapy, the anti-CD20 antibody rituximab is a central part of treatment. A question that has been debated is whether combining rituximab with the chemotherapy drug bendamustine (a regimen called BR) is better than rituximab alone. A large observational study in older patients with splenic or nodal MZL found no significant difference in event-free or overall survival between the two approaches. BR did, however, come with more toxicity, including higher rates of hospitalization and the need for blood transfusions, plus substantially higher costs.¹⁵ For older patients in particular, the simpler regimen may be the smarter choice.

For relapsed or refractory disease, Bruton tyrosine kinase (BTK) inhibitors have become an important option. MZL cells often depend on B-cell receptor signaling for survival, and BTK inhibitors block a critical step in that pathway. Ibrutinib, the first BTK inhibitor tested in this setting, produced responses in about 48% of previously treated patients, with a median progression-free survival of about 14 months.¹⁶ The next-generation BTK inhibitor zanubrutinib performed even better in the MAGNOLIA trial, achieving an overall response rate of about 68%, with a quarter of patients reaching complete remission. At two years, roughly 71% of responders had not progressed.¹⁷ Zanubrutinib is now approved specifically for MZL that has relapsed after prior treatment.

The Molecular Machinery Behind NF-κB

A thread running through all three MZL subtypes is overactivation of the NF-κB signaling pathway, which promotes B-cell survival and proliferation. Several of the chromosomal translocations seen in MALT lymphoma directly feed into this pathway. The three best-characterized translocations all converge on activating both the canonical and non-canonical arms of NF-κB, effectively giving the tumor cell a constant “survive and divide” signal that no longer depends on outside stimulation.¹⁸ A meta-analysis of genetic alterations across MZL subtypes identified NOTCH2 and TNFAIP3 as the most consistently mutated genes. TNFAIP3 normally acts as a brake on NF-κB, so when it is lost or mutated, the pathway stays switched on.¹⁹

Understanding that NF-κB is the central driver helps explain both why infection eradication works in early disease (removing the external stimulus collapses the signaling loop) and why it stops working once the tumor acquires intrinsic genetic changes that keep NF-κB active regardless. It also opens the door to therapies that target the pathway directly, though such drugs are still largely investigational for MZL.

Risk of Transformation to Aggressive Lymphoma

One of the concerns patients have is whether their indolent lymphoma can become something more dangerous. MZL can transform into diffuse large B-cell lymphoma (DLBCL), an aggressive cancer that requires intensive chemotherapy. A population-based study using over 420 transformation events found that the overall 10-year cumulative incidence of transformation was about 2.2%. The risk was not evenly distributed across subtypes: splenic MZL had the highest rate at roughly 5.8%, nodal MZL about 2.7%, and extranodal MZL the lowest at around 1.5%.²⁰

These numbers are reassuring for most patients. Transformation is uncommon, and extranodal MALT lymphoma, the most frequent subtype, has the lowest risk. Still, anyone with MZL should be aware of the warning signs: rapidly growing lymph nodes, new B-symptoms like drenching night sweats or unexplained weight loss, and a sudden rise in the blood marker LDH. Any of these warrants prompt evaluation with repeat biopsy.

Predicting Who Will Do Well

For a disease as variable as MZL, having a way to sort patients into risk categories is valuable. A recently developed prognostic index called the MZL-IPI uses five clinical factors to define low, intermediate, and high-risk groups. In the study that created it, patients with no adverse factors had a five-year progression-free survival of 85%, those with one or two factors were at 66%, and those with three or more dropped to 37%. The model was validated in an independent cohort of over 350 patients.²¹

For extranodal MALT lymphoma specifically, the Revised MALT-IPI uses four disease characteristics, including age over 60, elevated LDH, advanced stage, and involvement of multiple mucosal sites, to stratify patients into four risk tiers. High-risk patients had more than eight times the hazard for progression compared with the lowest-risk group.²² These tools help clinicians decide who can be safely observed and who should begin treatment sooner.

Quality of Life After Diagnosis

A diagnosis of any cancer is psychologically jarring, and an indolent lymphoma brings its own peculiar stress: the disease may not be treated aggressively, which can leave patients feeling like nothing is being done. Data from a prospective cohort found that quality of life was broadly stable over the first five years after diagnosis regardless of whether the initial approach was active surveillance, rituximab-based therapy, or chemoimmunotherapy. Emotional well-being, in particular, was not worse among patients who were watched rather than treated, which should ease concerns about the observation approach.²³

The one area where the study flagged a decline was social and family well-being, things like support from friends, family communication, and closeness to a partner. That finding suggests the real unmet need for many MZL patients is not medical but psychosocial, and it supports the value of connecting patients to support groups or counseling alongside their oncology care.

MZL in Children and Adolescents

While MZL is overwhelmingly a disease of adults, pediatric cases exist and behave quite differently. Pediatric nodal MZL primarily affects male adolescents, typically presents as painless swelling in the head and neck region, and is almost always caught at an early stage. It is considered a distinct entity from adult nodal MZL, with fewer genetic abnormalities and an even more indolent course.²⁴

Outcomes in children are excellent. In one series of 66 pediatric MZL patients, overall survival was 98%. Most children with nodal MZL were managed with surgical removal of the affected lymph node followed by observation, without chemotherapy. Relapses occurred in about 17% of the total group, but nearly all were in the extranodal MALT subtype rather than the nodal form.²⁵ For parents receiving this diagnosis, the data is strongly reassuring: the vast majority of children do extremely well with minimal treatment.

CAR-T Cells and the Next Frontier

The biggest shift in lymphoma treatment over the past decade has been chimeric antigen receptor (CAR) T-cell therapy, in which a patient’s own immune cells are engineered to attack cancer. CAR-T has been transformative for aggressive B-cell lymphomas, but its use in indolent subtypes like MZL has lagged behind. Early data in follicular lymphoma have been encouraging, and MZL-specific trials are beginning to generate results, though published evidence remains thin. For now, anti-CD20-based regimens, lenalidomide plus rituximab, and BTK inhibitors remain the standard options for relapsed MZL. Whether CAR-T will find a defined role depends on whether the deep remissions seen in aggressive lymphoma translate to a disease that already has a long natural history and relatively good outcomes with existing treatments. The real question is not whether CAR-T can work in MZL but whether the benefit justifies the toxicity and cost for a cancer that many patients live with for years.