Step 1 topics → Gastrointestinal → MALT Lymphoma

MALT Lymphoma

USMLE Step 1 trap: Overlooks H. pylori eradication as potentially curative monotherapy for low-grade gastric MALT lymphoma. H. pylori eradication alone achieves remission in the majority of low-grade, localized gastric MALT lymphomas; chemotherapy or radiation is reserved for H. pylori-negative or high-grade disease.

MALT lymphoma (mucosa-associated lymphoid tissue lymphoma) is a low-grade B-cell marginal zone lymphoma that arises from acquired lymphoid tissue in the gastric mucosa — tissue that shouldn't be there in the first place. In a healthy stomach, there is essentially no organized lymphoid tissue. H. pylori infection triggers chronic mucosal inflammation, which recruits lymphocytes and creates the substrate from which malignant B-cell clones can emerge. USMLE Step 1 tests this as a model case of infection-driven malignancy, so you need to understand the whole chain: H. pylori → chronic antigen stimulation → B-cell clonal expansion → MALT lymphoma.

The exam approaches this from two main angles. The first is mechanism — specifically, how H. pylori promotes B-cell transformation. The second is management — and this is where most students lose points, because the treatment logic here is genuinely counterintuitive. The exam will present a patient with low-grade, localized gastric MALT lymphoma and ask what you do first. The right answer is H. pylori eradication, not chemotherapy. That logic only makes sense if you understand the pathogenesis: if the lymphoma is antigen-driven, remove the antigen and you remove the survival signal. The t(11;18) translocation adds a layer of complexity that USMLE Step 1 will occasionally probe — knowing it predicts eradication failure separates strong students from average ones.

What makes this concept tricky is the collision of several distinct ideas: microbiology (H. pylori), immunology (T-cell help, antigen-driven B-cell survival), molecular pathology (NF-κB, chromosomal translocations), and clinical management — all wrapped in a single disease. Students who memorize 'H. pylori causes MALT lymphoma' without understanding the mechanism will be lost when the exam asks about why eradication works, or what t(11;18) predicts.

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Common misconceptions

Common mistake
Wrong: H. pylori eradication is ineffective for MALT lymphoma and chemotherapy is always required.
Right: H. pylori eradication alone achieves remission in the majority of low-grade, localized gastric MALT lymphomas; chemotherapy or radiation is reserved for H. pylori-negative or high-grade disease.
H. pylori eradication is actually the primary — and often only — treatment needed for low-grade, localized gastric MALT lymphoma, achieving remission in roughly 70-80% of cases. The logic follows directly from pathogenesis: the lymphoma depends on continuous antigen-driven T-cell signals for B-cell survival, so eliminating H. pylori removes that stimulus. Chemotherapy and radiation are reserved for H. pylori-negative disease, high-grade transformation (diffuse large B-cell lymphoma), or cases with the t(11;18) translocation that predicts eradication failure.
Common mistake
Wrong: H. pylori directly transforms B cells into lymphoma cells via oncogenic gene insertion.
Right: H. pylori drives chronic T-cell stimulation that provides antigen-dependent survival signals to autoreactive B cells in the gastric mucosa, promoting their clonal expansion into MALT lymphoma.
H. pylori does not directly insert genes into B cells or act as a classical oncovirus. Instead, it drives a chronic inflammatory response in the gastric mucosa that recruits T cells, which in turn provide antigen-dependent survival and proliferation signals to autoreactive B cells. Over time, this sustained stimulation favors clonal selection of B cells that have acquired mutations allowing them to proliferate even with lower levels of T-cell help — ultimately producing lymphoma. This indirect, immunologically mediated mechanism is exactly why removing the antigen (via eradication) can reverse early disease.
Common mistake
Gap: Missing that t(11;18) translocation in MALT lymphoma predicts failure of H. pylori eradication alone
The t(11;18) translocation in gastric MALT lymphoma produces an API2-MALT1 fusion protein that constitutively activates NF-κB and predicts resistance to H. pylori eradication therapy.
The t(11;18)(q21;q21) translocation fuses the API2 gene (an apoptosis inhibitor) to MALT1 (a signaling protein), creating a fusion protein that locks NF-κB in a constitutively active state. This means the B cells no longer need H. pylori-derived antigen signals to survive and proliferate — the oncogenic driver is now cell-intrinsic. Clinically, this translocation predicts that H. pylori eradication alone will fail, so these patients need radiation or chemotherapy from the start. On USMLE Step 1, if a question mentions t(11;18) in the context of gastric MALT lymphoma, it's signaling that eradication-first strategy is not appropriate.
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What the exam tests

  1. Understand the step-by-step mechanism by which chronic H. pylori infection drives clonal B-cell expansion into MALT lymphoma — specifically the role of antigen-dependent T-cell help providing survival signals to autoreactive B cells in the gastric mucosa.
  2. Know the first-line treatment for low-grade, H. pylori-positive, localized gastric MALT lymphoma is H. pylori eradication alone, and understand when to escalate to chemotherapy or radiation (H. pylori-negative disease, high-grade transformation, or eradication failure).
  3. Recognize that the t(11;18) translocation produces an API2-MALT1 fusion protein that constitutively activates NF-κB, making the lymphoma antigen-independent — and therefore predict that these tumors will not respond to H. pylori eradication alone.

Can you avoid these mistakes?

A 58-year-old man is found on endoscopic biopsy to have low-grade gastric MALT lymphoma. H. pylori testing is positive. Staging shows disease limited to the stomach with no lymph node involvement. What is the most appropriate next step in management, and what is the underlying rationale?
A patient with low-grade gastric MALT lymphoma is told that antibiotics alone could make his lymphoma regress. He's skeptical — it sounds like magic. Explain the mechanism: what would have to be true about the lymphoma's biology for H. pylori eradication to work, and what would make it fail?
A patient with gastric MALT lymphoma undergoes cytogenetic testing and is found to have the t(11;18) translocation. How does this change your management plan compared to a patient without this translocation, and why?
A classmate says: 'H. pylori causes MALT lymphoma the same way EBV causes Burkitt lymphoma — it directly transforms the B cells.' What is wrong with this model, and what is the correct mechanism?

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