Exclusive detection of the t(11;18)(q21;q21) in extranodal marginal zone Bcell lymphomas (MZBL) of MALT type in contrast to other MZBL and extranodal large B cell lymphomas

Extranodal mucosa-associated lymphoid tissue (MALT)-type lymphomas and noda l and splenic marginal zone B cell lymphomas (MZBL) share morphological and immunophenotypic features with marginal zone B cells of reactive lymphoid tissues. Although displaying a similar immunophenotype, recent investigatio ns suggest fundamental genetic differences among these subgroups. To determ ine the prevalence of the t(11;18) in a larger series of MALT-type lymphoma s and to investigate a possible occurrence in other lymphomas, we screened 106 non Hodgkin's lymphomas (NHL) by interphase cytogenetics using yeast ar tificial chromosome (YAC) probes flanking the breakpoint at 11q21. A signal constellation indicating a disruption in 11q21 and thus pointing to the pr esence of the t(11;18) was observed in 9 of 33 (27%) low-grade lymphomas of MALT type. The complete absence of t(11;18)-positive cells in 32 primary a nd secondary extranodal high-grade lymphomas suggests that low-grade lympho mas of MALT type characterized by the t(11;18) are unlikely to transform in to high-grade tumors. The absence of tumor cells carrying the t(11;18) in n odal MZBL challenges the assumption that most, if not all, of these tumors represent the nodal manifestation of a so far undetected low-grade lymphoma of MALT type. The t(11;18) was not detected in a single case of 29 splenic MZBL investigated. This observation strengthens the view that splenic MZBL are biologically different from extranodal MZBL of MALT type.