 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. "    ///    "Analysis of API2-MALT1 fusion, trisomies, and immunoglobulin VH genes in pulmonary mucosa-associated lymphoid tissue lymphoma.. "    ///    One case showed API2-MALT1 fusion and trisomy 3.     ///    MALT1 gene abnormalities were concordant with API2-MALT1 fusion or trisomy 18.     ///    "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. "    ///    "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. "    ///    "In addition, both mutated and unmutated tumor cases were found to carry the API2-MALT1 fusion and trisomy 3. "