The t(11;18)(q21;q21) chromosome translocation is a frequent and specific aberration in low-grade but not high-grade malignant non-Hodgkin's lymphomas of the mucosa-associated lymphoid tissue (MALT-) type.

Primary extranodal malignant non-Hodgkin's lymphoma arising from the mucosa-associated lymphoid tissue (MALT-type lymphoma) represents a subtype of B-cell lymphoid malignancies with distinct clinicopathological features and is often associated with a favorable prognosis. Unlike the situation in nodal non-Hodgkin's lymphoma of B-cell lineage, few data are still available concerning the chromosomal constitution of MALT-type lymphomas. Until now, cytogenetic data from 29 low-grade MALT lymphomas with karyotypic alterations have been reported from different institutions, and virtually no data were available for high-grade MALT-type lymphomas. We have analyzed the cytogenetics of 44 MALT lymphomas arising in the stomach, parotid gland, thyroid gland, lung, breast, and conjunctiva. Clonal chromosome aberrations have been detected in 13 of 20 (65%) low-grade and 20 of 24 (83%) high-grade tumors. More than half of the low-grade lymphomas with abnormal karyotypes (7 of 13 cases, 53%) displayed clonal t(11;18)(q21;q21), thus specifically associating this translocation with MALT-type lymphomas for the first time in a larger series. In contrast, t(11;18) was not found in a single case of 20 high-grade MALT-type lymphomas with abnormal karyotypes, nor were translocations t(14;18) or t(3;14), characterizing about 10-35% of primary nodal large cell lymphomas. Instead, these lymphomas were associated with t(8;14)(q24;q32) in three cases, frequent deletions in the long arm of chromosome 6, and partial or whole gains of chromosomes 3, 7, 17, 18, and 21.