Analysis of API2-MALT1 fusion, trisomies, and immunoglobulin VH genes in pulmonary mucosa-associated lymphoid tissue lymphoma.

Pulmonary mucosa-associated lymphoid tissue lymphoma is unique in that chronic inflammation is rare and that API2-MALT1 fusion, resulting from t(11;18)(q21;q21), occurs frequently. In this study, we examined 20 cases for API2-MALT1 fusion using the multiplex reverse-transcription polymerase chain reaction and looked for trisomy 3, trisomy 18, and abnormalities of MALT1 and IGH genes using fluorescence in situ hybridization. In addition, we analyzed VH genes by subcloning of the monoclonal polymerase chain reaction products. Of 20 cases studied, we detected gene abnormalities in 16: API2-MALT1 fusion in 9, trisomy 3 in 5, trisomy 18 in 4, MALT1 abnormality in 13, and IGH abnormality in 1. MALT1 gene abnormalities were concordant with API2-MALT1 fusion or trisomy 18. One case showed API2-MALT1 fusion and trisomy 3. On detection of API2-MALT1 fusion and trisomies, we were able to divide our cases into 3 groups, API2-MALT1 positive, trisomy positive, and no detectable gene abnormality, suggesting that tumor development had processed along different genetic pathways. All 20 cases were analyzed for VH genes. Most of the VH genes selected by the lymphomas belonged to the VH3 family, but there was no restriction to any particular VH fragment. Of interest, VH genes were unmutated in 7 cases, suggesting that T-cell-independent extrafollicular B-cell maturation may be important in the development of this lymphoma. In addition, both mutated and unmutated tumor cases were found to carry the API2-MALT1 fusion and trisomy 3. This observation suggests that these gene abnormalities may occur in microenvironments found before or outside of follicular germinal centers.