Sjögren's Syndrome and MALT Lymphomas of Salivary Glands: A DNA-Cytometric and Interphase-Cytogenetic Study

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 mucosa-associated lymphoid tissue (MALT)–type lymphoma. The majority of salivary gland MALT lymphomas are thought to develop from longstanding Sjögren'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 1of 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.