Marginal zone lymphoma (MALT lymphoma)

Overview

MALT lymphoma is an extranodal marginal zone B-cell lymphoma - a low-grade, indolent B-cell non-Hodgkin's lymphoma driven by chronic antigen stimulation from infection or autoimmunity.

Presentation

•Gastric - epigastric pain/dyspepsia indistinguishable from peptic ulcer disease; nausea, early satiety

•Thyroid - new or enlarging goitre in a patient with known Hashimoto's thyroiditis

•Salivary gland - parotid/submandibular mass, especially in Sjögren's syndrome

•Constitutional (B) symptoms are uncommon; their presence raises concern for transformation to DLBCL

Investigations

🏆 Gold standard

•tissue biopsy with histopathology and immunophenotyping - CD20+, CD5-, CD10- centrocyte-like B-cells

•Gastric disease: upper GI endoscopy with multiple biopsies - histology, H. pylori status, t(11;18) testing

•H. pylori testing: urea breath test, stool antigen, or rapid urease test on biopsy

•CT chest/abdomen/pelvis - staging; PET-CT if transformation to DLBCL suspected

•LDH - elevated LDH suggests higher tumour burden or transformation

Management

•Gastric MALT, H. pylori-positive (localised): H. pylori eradication therapy alone - achieves complete histological remission in ~70-80%; one of the few malignancies curable with antibiotics

•Gastric MALT, H. pylori-negative or t(11;18)+, or non-gastric localised disease: involved-field radiotherapy

•Disseminated or refractory disease: chemoimmunotherapy

•After H. pylori eradication: repeat endoscopy with biopsies at ~3 months to assess response, then ongoing annual surveillance

Aetiology - key associations

•H. pylori - gastric MALT lymphoma (most common association overall)

•Hashimoto's thyroiditis - thyroid MALT lymphoma; ~60-80x increased risk of thyroid lymphoma

•Sjögren's syndrome - salivary gland and orbital MALT lymphoma

•Chlamydia psittaci - ocular adnexal MALT lymphoma

⚠️

The t(11;18)(q21;q21) translocation (API2-MALT1) is found in ~25-40% of gastric MALT lymphomas. It renders the lymphoma independent of H. pylori antigen stimulation - H. pylori eradication will NOT induce remission; escalate to radiotherapy or chemoimmunotherapy.

Complications and prognosis

•Transformation to DLBCL - most important complication; suspect if rapid lymph node enlargement, new B symptoms, or sharply rising LDH

•Late relapse - can occur years to decades after remission; lifelong surveillance required

•5-year overall survival for localised gastric MALT lymphoma exceeds 90%; prognosis worse with t(11;18), disseminated disease, or DLBCL transformation

🎯

Hashimoto's thyroiditis and Sjögren's syndrome both increase MALT lymphoma risk - a new mass in either context should prompt urgent investigation for lymphoma.