MALT lymphoma (mucosa‑associated lymphoid tissue lymphoma) is a subtype of extranodal marginal‑zone B‑cell lymphoma that arises from lymphoid tissue normally present in the mucosal linings of various organs. It is classified by the World Health Organization (WHO) as “extranodal marginal zone lymphoma of mucosa‑associated lymphoid tissue.”
Epidemiology
MALT lymphoma accounts for approximately 7–8 % of all non‑Hodgkin lymphomas. It most commonly involves the stomach, but can also arise in the salivary glands, thyroid, lung, ocular adnexa, intestine, skin, and breast. The disease typically presents in middle‑aged to older adults, with a slight female predominance in gastric cases.
Pathogenesis
The development of MALT lymphoma is closely linked to chronic antigenic stimulation and inflammation. In the stomach, infection with Helicobacter pylori induces the formation of acquired lymphoid tissue in the gastric mucosa, providing a microenvironment that can give rise to clonal B‑cell proliferation. Similar mechanisms involve autoimmune diseases such as Sjögren’s syndrome (salivary gland MALT lymphoma) and Hashimoto thyroiditis (thyroid MALT lymphoma). Genetic alterations frequently observed include translocations involving the MALT1 gene (t(11;18)(q21;q21) API2‑MALT1) and mutations activating NF‑κB signaling pathways.
Clinical Presentation
Symptoms depend on the site of involvement. Gastric MALT lymphoma often presents with dyspepsia, epigastric pain, or is discovered incidentally during endoscopy. Extra‑gastric sites may cause mass effect, organ‑specific dysfunction, or painless swelling (e.g., a parotid mass in salivary‑gland disease). Systemic “B‑symptoms” (fever, night sweats, weight loss) are uncommon at presentation.
Diagnosis
Diagnosis requires histopathologic examination of biopsy tissue demonstrating infiltrates of small‑to‑medium‑sized CD20⁺ B‑cells with marginal‑zone features, often accompanied by reactive germinal centers. Immunophenotyping typically shows positivity for CD20, CD79a, BCL2, and negativity for CD5, CD10, and cyclin D1. Molecular studies may detect the characteristic t(11;18)(q21;q21) translocation. Staging incorporates imaging (CT, PET/CT), endoscopic ultrasound for gastric disease, and bone‑marrow evaluation when indicated.
Treatment
Therapeutic strategies are tailored to the anatomic site and disease stage. For early‑stage gastric MALT lymphoma, eradication of H. pylori with appropriate antibiotic therapy leads to remission in 70–80 % of cases. In H. pylori‑negative or refractory gastric disease, radiotherapy (30–36 Gy) is effective. For non‑gastric or advanced disease, treatment options include immunochemotherapy (e.g., rituximab alone or combined with chlorambucil or bendamustine), surgery for localized lesions, and targeted agents such as ibrutinib in selected cases. The presence of the t(11;18) translocation predicts resistance to antibiotic therapy.
Prognosis
MALT lymphoma generally has an indolent clinical course with a favorable overall survival; 5‑year survival rates exceed 85 % in most series. Relapse can occur, particularly in cases resistant to H. pylori eradication or those with adverse genetic features. Long‑term follow‑up with endoscopic surveillance (for gastric disease) or imaging is recommended.
Research and Emerging Therapies
Ongoing investigations explore the role of novel agents targeting the NF‑κB pathway, immune checkpoint inhibitors, and CAR‑T cell therapy for refractory MALT lymphoma. Molecular profiling continues to refine risk stratification and therapeutic decision‑making.
References
(Encyclopedic entries are synthesized from peer‑reviewed medical literature, WHO classification of tumours of haematopoietic and lymphoid tissues, and current clinical guidelines.)