Canterbury DHB

MALT Lymphoma

Diagnosis, staging and management present unique problems in MALT lymphoma. 50% of these tumours have their origin in the GI tract, and of these 85% arise in the stomach. The other common sites are the lungs, head and neck, orbit, skin and thyroid.

Dissemination occurs in 35% of MALT without obviously altering their outcome, so extensive staging procedures may not be justified.

Distinguishing reactive from a malignant process can cause difficulty in the interpretation of MALT histology. Tumour cells express surface Ig and show light chain restriction. They are CD20+, 79a+, CD43 weak, CD21+ and 35+. They are negative for 5, 10 and 23 antigens. There is no specific phenotype. Cytogenetic abnormalities include trisomy 3 in 60%, and t(11;18) in 25 - 50%. The translocation t(11;18) is found in all cases of Helicobacter pylori (HP) negative and only 2% of HP positive gastric MALToma.

Management

Helicobacter pylori is present in 90% of gastric MALToma. Both HP positive and negative gastric MALToma should receive triple therapy.

Other associations between MALT lymphoma and infection have been shown which should be treated appropriately; Chlamydia psittaci – doxycycline; Borellia burgdorferi (cutaneous MALT) – doxycycline; Campylobacter (immunoproliferative small intestinal disease) - erythromycin.

Anti-tumour treatments

• In low bulk stage IE disease HP eradication therapy alone may be used as initial therapy followed by surveillance endoscopies. Many clinicians follow this with chlorambucil (e.g. 6 mg/m²/day for 14 days repeated every 28 days for 6 courses). If no further therapy is given, follow-up should be continued indefinitely as it is not known whether antibiotic therapy alone can cure the lymphoma.
• Localised disease may be cured with local treatment (surgery or radiotherapy). Dissemination occurs in approximately 30% of cases and these patients require management similar to that given for other low-grade lymphomas.
• Transformation to diffuse large B cell lymphoma may occur and is treated as de novo DLBCL. Triple eradication therapy should still be given to eliminate any residual low grade component.

Topic Code: 5987