GENETIC-EVIDENCE FOR A CLONAL LINK BETWEEN LOW AND HIGH-GRADE COMPONENTS IN GASTRIC MALT B-CELL LYMPHOMA

High-grade MALT lymphomas often contain low-grade tumour components; b oth cell populations have been shown to express the same immunoglobuli n light chain previously. However, the clonal link between the low and high-grade components has not been established at the genetic level. To investigate this link, we have examined low- and high-grade compone nts microdissected from tissue sections of four high-grade gastric MAL T lymphomas. PCR and sequence analyses were performed to identify clon e-specific rearranged immunoglobulin heavy chain gene sequences. In ea ch of these cases, the PCR products from the two components were ident ical in size by electrophoresis. Direct sequencing revealed common clo ne-specific immunoglobulin heavy chain gene rearrangements in both les ions of each case, providing genetic evidence for a clonal link. These results support the proposal that high-grade MALT lymphomas generally evolve from low-grade clones.