MALT Lymphoma Types
MALT lymphomas are classified by anatomic site of origin, with gastric MALT lymphoma being the most common (representing at least one-third of all cases), followed by non-gastric extranodal sites including ocular adnexa, salivary glands, thyroid, lung, skin, and small intestine 1, 2, 3.
Classification Framework
MALT lymphomas represent approximately 7% of all non-Hodgkin's lymphomas in the Western world and are formally classified as "extranodal marginal zone B-cell lymphomas of mucosa-associated lymphoid tissue type" 1. The key distinguishing feature is that these lymphomas can arise at any extranodal site where chronic antigenic stimulation occurs 1, 3.
Major Anatomic Subtypes
Gastric MALT Lymphoma
- Most common subtype (≥33% of all MALT lymphomas)
- Associated with chronic Helicobacter pylori infection in approximately two-thirds of cases 1
- Presents with non-specific upper GI complaints, typically showing non-specific gastritis or peptic ulcer on endoscopy rather than mass lesions 1
Non-Gastric MALT Lymphomas
The non-gastric sites include 2, 3, 4:
Ocular Adnexal MALT Lymphoma (OAML)
- Linked to Chlamydia psittaci infection in certain geographic regions
- Characteristic clinical presentation related to orbital anatomy 4
Salivary Gland MALT Lymphoma
- Associated with Sjögren's syndrome
- Tends to show monocytoid cell morphology 4
Thyroid MALT Lymphoma
- Develops in the background of Hashimoto's thyroiditis
- Often displays plasmacytic differentiation 4
Pulmonary MALT Lymphoma
- Can be linked to chronic airway inflammation from Achromobacter xylosoxidans
- Characteristically shows lymphangitic distribution 3, 4
- Tends toward small lymphocyte morphology 4
Cutaneous MALT Lymphoma
Small Intestinal MALT Lymphoma
- Can be associated with Campylobacter jejuni infection 3
Other Sites
- Breast, dura, and other extranodal locations with characteristic anatomic presentations 4
Related Marginal Zone Lymphoma Subtypes
While the question focuses on MALT lymphomas specifically, it's important to note that the broader category of marginal zone lymphomas includes three distinct entities 2:
- Extranodal MZL of MALT type (the focus of this discussion)
- Splenic marginal zone lymphoma (SMZL)
- Nodal marginal zone lymphoma (NMZL)
These share overlapping morphologic features and mature B-cell phenotype (CD20+, CD5-, CD10-) but have distinct clinical behaviors and cytogenetic profiles 2.
Important Clinical Distinction
The term "high-grade MALT lymphoma" is no longer accepted in current WHO classification 1. Cases showing solid or sheet-like proliferation of transformed large cells must be diagnosed as diffuse large B-cell lymphoma, not MALT lymphoma 1. This distinction is critical for treatment planning and prognosis.
Unifying Pathogenic Theme
Despite the diverse anatomic sites, chronic antigenic stimulation—either infectious or autoimmune—is the unifying pathogenic mechanism across all MALT lymphoma subtypes 3, 4. This antigen-driven nature explains the site-specific infectious and autoimmune associations and underlies the rationale for antimicrobial or immunosuppressive therapies in certain subtypes.