Clonal analysis of multifocal low-grade MALT lymphomas

Abstract

Backgrounds: Low-grede MALT lymphoma is an indolent neoplasm which tends to remain localized for a long time before spreading. However, the tumor may disseminate preferentially to other mucosal sites without systemic spread. It is unclear the relationship between the different sites in the multifocal cases of low-grade MALT lymphoma. The aim of this study was to compare the clonal relationship of multifocai lesions of MALT lymphoma using the analysis of rearranged immunoglobulin heavy chain geoe (CDR3). Materials and Methods: Six cases of multifocal low-grade MALT lymphomas were investigated. The involved organs were stomach, duodenum, colon and liver. H.pylori infection was detected in 3 of 6 cases. DNA was microdissected from paraffin-embedded tissues using DEXPAT kit (Takara). PCR was performed to amplify the rearranged Ig heavy chain gene, using semi-nested PCR. Products were electrophoresed using a 3% agalose gel stained with cthidium bromide. The PCR products were ligated to the pGEM-T Easy Vector and the ligatiou mixtures were transformed into JMI09 high efficiency competent cells by using a TA Cloning Kit (Promega). The PCR products showing the expected insert size were sequenced using the ABI sequencer with dye terminators (ABI prism 310 Sequencing Analysis). A dominant clone was found in each of the samples and more than 10 different bacterial isolates were sequenced. Results: PCR amplification of the rearranged IgH genes yielded the same sized dominant product in 4 of 6 cases and sequences of them were same. But 2 cases showed that the dominant clones were different in each site of multifocal lesions. One case of the gastric and colonic lesions showed that oligoclonal clones, which were completely different from those of colonic lesions, were identified. Another was the case of hepatic MALT lymphoma followed by gastric and colonic MALT lymphoma two years later. The hepatic MALT lymphoma showed biclonal clones with the same nucleotide sizes, one clone of which was the same sequence as that of the gastric and colonic lesions. These two cases showed negative H.pylori infection. Conclusions: The present study suggested that some of muitifocal low-grade MALT lymphomas may originate from the different organ independently.