Detection of API2-MALT1 fusion gene in extranodal B-cell lymphoma and its significance

Abstract

To study the expression of API2-MALT1 mRNA in mucosa-associated lymphoid tissue (MALT) lymphoma, extranodal diffuse large B-cell lymphoma (DLBCL) and Hashimoto's thyroiditis, to investigate the expression pattern of API2-MALT1 variants, and to correlate the findings with the clinicopathologic features and prognosis. Sixty-two cases of MALT lymphoma (10 from lung, 31 from stomach, 9 from intestine and 12 from thyroid), 32 cases of extranodal DLBCL (16 from stomach, 13 from intestine and 3 from thyroid), 8 cases of Hashimoto's thyroiditis and 5 cases of reactive lymph nodes hyperplasia as negative controls were collected. The expression of API2-MALT1 mRNA was studied in all cases by reverse transcriptase (RT)-polymerase chain reaction (PCR) and nested PCR. The 94 cases of lymphoma were subdivided into API2-MALT1-positive and API2-MALT1-negative groups. Among the patients, 78 were followed up for 6 to 120 months. The differences in clinicopathologic features and prognosis between the two groups were analyzed. API2-MALT1 transcripts were detected in 39 of the 94 lymphoma cases (with 28 cases being MALT lymphoma and 11 cases being extranodal DLBCL). mRNA expression was not detected in all cases of Hashimoto's thyroiditis and the negative controls. Two fusion gene variants, A1446-M1123 and A1446-M814 were found, and A1446-M1123 expression was more common. As for MALT lymphoma cases, the frequency of the fusion gene expression was lower in thyroid, when compared with that in lung, stomach and intestine. API2-MALT1-positive cases had tumors in an earlier stage with milder infiltration of cancer cells, lower relapse rate, and higher five-year survival rate. The expression of API2-MALT1 mRNA can be detected in both MALT lymphoma and extranodal DLBCL, but not in Hashimoto's thyroiditis. These cases tend to show a more indolent clinical course and better survival. The frequency of t (11; 18) (q21; q21) correlates with the primary sites of MALT lymphoma. The higher incidence of breakpoint at 1123 bp of MALT1 gene in Chinese people may be due to geographical variation.