Objective: To study the frequency of certain specific genetic aberrations, including t (11; 18)/API2-MALT1, t (1; 14)/IgH-bcl-10 and t (14; 18)/IgH-MALT1, in mucosa-associated lymphoid tissue (MALT) lymphoma of different sites.
Methods: One hundred and ninety-six cases of MALT lymphoma from Cancer Hospital of Fudan University were enrolled into the study. The samples consisted of MALT lymphomas from stomach (53 cases, including 44 cases of low-grade MALT lymphoma and 9 cases of MALT lymphoma with diffuse large B-cell lymphoma component), ocular adnexa (50 cases), salivary gland (20 cases), lung (20 cases), intestine (17 cases), skin (17 cases), liver (8 cases), thyroid (5 cases) and other sites (2 cases from tongue, 1 case from pancreas, 1 case from larynx, 1 case from vocal cords and 1 case from kidney). Fluorescence in-situ hybridization for API2-MALT1 fusion gene, bcl-10, MALT1 and IgH genes was performed on paraffin sections.
Results: Among the 196 cases of MALT lymphoma, 25 cases (12.8%) possessed API2-MALT1 fusion gene. The positive rates in various sites were significantly different (P = 0.002), as follows: 45.0% (9/20) in lung, 22.7% (10/44) in stomach (without large cell component), 15.0% (3/20) in salivary gland, 2 of 17 cases in intestine and 2.0% (1/50) in ocular adnexa. The fusion gene was not detected in the 9 cases of gastric MALT lymphoma with large cell transformation. It was also negative in the MALT lymphomas from skin, thyroid and other sites. One of the pulmonary MALT lymphoma cases showed simultaneous aberrations of IgH and MALT1 genes, such as t (14; 18)/IgH-MALT1. Two of the gastric MALT lymphoma cases without large cell transformation and one of the pulmonary MALT lymphoma cases showed aberrations in both IgH and bcl-10 genes, such as t (1; 14)/IgH-bcl-10. Six cases of MALT lymphoma, including 2 cases from salivary gland, 2 cases from liver, 1 case from thyroid and 1 case from stomach (large cell transformation), showed trisomy 18. On the other hand, 3 cases, including 2 cases from stomach and 1 case from intestine, showed MALT1 gene amplification.
Conclusions: In general, specific genetic aberrations have a relatively low frequency of occurrence in MALT lymphomas. The positive rates however show a remarkable difference in tumors of different anatomic sites. This phenomenon may suggest that MALT lymphomas in different sites, though sharing similar morphologic features, may have a divergent tumorgenesis.