Step 1 topics → Hematology and Oncology → Marginal Zone, MALT, and T-Cell Lymphomas

Marginal Zone, MALT, and T-Cell Lymphomas

USMLE Step 1 trap: Recommends chemotherapy as first-line for gastric MALT lymphoma rather than H. pylori eradication. Early-stage gastric MALT lymphoma associated with H. pylori is treated first with H. pylori eradication, which induces remission in the majority of cases.

Marginal zone, MALT, and T-cell lymphomas are a collection of lower-profile but highly testable entities on USMLE Step 1. The exam loves them because each has a specific antigen trigger — and the most common wrong first-line answer for early gastric MALT lymphoma is chemotherapy. H. pylori drives gastric MALT by chronically stimulating B cells; eradicate the bacteria and you remove the proliferative signal, inducing remission in most early-stage cases. The other key misconception: ATLL is caused by HTLV-1, not EBV — students default to EBV because it's the go-to viral lymphoma cause, but ATLL is strictly HTLV-1 with a distinct geography (Japan, Caribbean) and clinical picture. Each entity here requires mechanistic reasoning to answer questions correctly, not just recall of names.

The trickiest part of this cluster is the T-cell side. Mycosis fungoides and Sézary syndrome share a cell of origin (malignant CD4+ T cells) and similar skin findings, which makes students treat them as the same disease at different stages — they are not. USMLE Step 1 specifically tests whether you understand that Sézary syndrome is a leukemic phase with circulating malignant cells in the blood, not just worsening skin disease. Similarly, ATLL gets confused with EBV-associated lymphomas because students default to EBV as their go-to viral lymphoma cause — but ATLL is strictly HTLV-1, with a very different geography and clinical picture.

For MALT lymphoma, the key concept is antigen-driven lymphoma proliferation. H. pylori drives gastric MALT by chronically stimulating B cells through T-cell intermediaries, and removing the antigen (eradicating H. pylori) removes the proliferative signal. Students who don't internalize this mechanism default to chemotherapy, which is wrong for early-stage disease. Non-gastric MALT sites are driven by different antigens — autoimmune diseases like Sjögren's and Hashimoto's are the classic associations there.

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Common misconceptions

Common mistake
Wrong: Gastric MALT lymphoma requires immediate chemotherapy as first-line treatment.
Right: Early-stage gastric MALT lymphoma associated with H. pylori is treated first with H. pylori eradication, which induces remission in the majority of cases.
Gastric MALT lymphoma is not a spontaneously proliferating cancer in the traditional sense — it is driven by chronic antigen stimulation from H. pylori through activated T cells that signal B-cell proliferation. This means the treatment logic follows the cause: eradicate H. pylori first, and you remove the proliferative stimulus. In early-stage disease, this alone induces remission in the majority of cases. Jumping to chemotherapy skips the mechanism and is incorrect as first-line therapy.
Common mistake
Wrong: Sézary syndrome is simply a more advanced skin-limited form of mycosis fungoides.
Right: Sézary syndrome is the leukemic phase of cutaneous T-cell lymphoma with circulating malignant CD4+ T cells (Sézary cells) in the blood, whereas mycosis fungoides is confined to the skin.
Mycosis fungoides and Sézary syndrome are related but not simply different stages of skin disease. Mycosis fungoides is a skin-confined T-cell lymphoma that progresses through patch, plaque, and tumor stages — all in the skin. Sézary syndrome is defined by the presence of malignant CD4+ T cells (Sézary cells, with cerebriform nuclei) circulating in the peripheral blood, making it a leukemic phase. The distinction matters clinically and on USMLE Step 1 because Sézary carries a worse prognosis and different management.
Common mistake
Wrong: Adult T-cell leukemia/lymphoma (ATLL) is caused by EBV.
Right: ATLL is caused by HTLV-1 (human T-lymphotropic virus type 1), endemic to Japan, the Caribbean, and parts of Africa, and is distinct from EBV-associated lymphomas.
EBV causes several lymphomas (Burkitt's, post-transplant lymphoproliferative disease, some Hodgkin's), so it's tempting to assign it to ATLL — but ATLL is caused by HTLV-1, a completely different retrovirus. HTLV-1 is endemic to southwestern Japan, the Caribbean basin, and parts of Africa, and it transforms CD4+ T cells directly. The clinical picture of ATLL — hypercalcemia, skin lesions, circulating malignant T cells — is distinct from EBV-driven B-cell lymphomas, and knowing the virus is essential for correctly answering vignettes that describe the geography or exposure history.
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What the exam tests

  1. Know the common sites of MALT lymphoma (stomach, salivary glands, thyroid, lung) and the specific infection or autoimmune condition that drives lymphoma at each site — H. pylori for gastric, Sjögren's for salivary gland/lacrimal, Hashimoto's thyroiditis for thyroid.
  2. Distinguish mycosis fungoides from Sézary syndrome based on whether malignant CD4+ T cells are confined to skin (mycosis fungoides) or are circulating in the blood as Sézary cells (Sézary syndrome, which is the leukemic phase).
  3. Identify ATLL by its causative virus (HTLV-1, not EBV), its endemic geography (Japan, Caribbean, parts of Africa), and its clinical hallmarks including hypercalcemia, lytic bone lesions, skin involvement, and aggressive course.

Can you avoid these mistakes?

A 55-year-old woman from Kyushu, Japan presents with skin rash, hypercalcemia, and circulating lymphocytes with irregular nuclei on peripheral smear. What virus is responsible, and what cell type is malignant?
A patient with early-stage gastric MALT lymphoma tests positive for H. pylori on urea breath test. Before initiating any chemotherapy or rituximab, what is the correct first-line management and what is the expected response?
A dermatology patient has had a pruritic, erythematous skin rash for years that has progressed to plaques. Biopsy shows epidermotropic CD4+ T cells with cerebriform nuclei. A complete blood count now shows circulating atypical lymphocytes with the same morphology. How does this change the diagnosis from mycosis fungoides?
Which autoimmune conditions are classically associated with non-gastric MALT lymphoma development, and at which anatomic sites do they typically produce MALT lymphoma?

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