Sjogren's syndrome and MALT lymphomas of salivary glands: A DNA- cytometric and interphase-cytogenetic study

Abstract

Few and conflicting cytogenetic data are available concerning the chromosomal constitution of (mainly gastric) extranodal marginal zone B-cell non-Hodgkin's lymphoma arising from mucosaassociated lymphoid tissue (MALT)- type lymphoma. The majority of salivary gland MALT lymphomas are thought to develop from longstanding Sjogren's syndrome/benign lymphoepithelial lesion (BLEL). We tried to achieve a better comprehension of related cytogenetic alterations by comparing DNA-ploidy and numerical chromosomal aberrations, assessed by different techniques of DNA cytometry (image cytometry) and interphase cytogenetics using nonradiographic in situ hybridization (centromere specific probes for 3, 7, 12, 18) on 12 cases of BLEL, 13 low- grade MALT lymphomas (LG-MALT-L) and 4 high-grade MALT lymphomas (HG-MALT-L) of salivary gland. Both techniques were applied on tissue sections preferentially, enabling a reliable measurement of histomorphologically identified areas. No case of BLEL showed cytogenetic abnormalities. Three of 4 HG- and 2 of 13 LG-MALT-L exhibited complex chromosomal gains in nonisotopic in situ hybridization, which were reflected by DNA nondiploidy in image cytometry. In 6 of 13 LG- and 1 of 4 HG-MALT-L, one or two numerical chromosomal aberrations were demonstrated by nonisotopic in situ hybridization, which could not be resolved by image cytometry. In the 11 DNA- diploid LG-MALT-L, trisomies 18, 3, and 12 were found in 36, 12, and 9%, respectively. In conclusion, comparing BLEL, which showed no chromosomal aberrations, with LG- and HG-MALT-L, an increase in frequency and number of numerical aberrations and DNA nondiploidy was seen. Peritetraploid DNA nondiploidy might be characteristic for HG-MALT-L of salivary gland as it is a rare finding in MALT lymphomas of other sites. It is unclear whether the documented chromosomal aberrations in LG-MALT-L, especially increased rate of trisomy 18, indicate a pathogenic impact or merely reflect genetic instability.