API2-MALT1 Fusion Gene in Colorectal Lymphoma

The API2-MALT1 fusion gene was originally identified from a t(11;18)(q21;q21) translocation, a specific chromosomal abnormality that is found in mucosa-associated lymphoid tissue (MALT) lymphoma. Gastric MALT lymphomas positive for the API2-MALT1 fusion gene do not respond to Helicobacter pylori–eradication therapy, but otherwise, the incidence and clinicopathological behavior of colorectal MALT lymphoma with this genetic abnormality are unclear. We examined the API2-MALT1 fusion by multiplex RT-PCR method in 47 cases of MALT lymphoma and 13 cases of diffuse large B-cell lymphoma and evaluated the relevance of API2-MALT1 positivity to the clinical and pathological features. The mean ages of MALT lymphoma and diffuse large B-cell lymphoma patients were 65 (range, 37–87 y) and 58 (range, 14–85 y) years, respectively. API2-MALT1 fusion genes were detected in seven cases (15%) of MALT lymphoma and one case (8%) of diffuse large B-cell lymphoma. In MALT lymphomas, the tumor size in API2-MALT1–positive cases was 62 plusminus 39 mm (mean plusminus SD), statistically larger than that in API2-MALT1–negative cases (25 plusminus 19 mm; P < .01). The API2-MALT1–positive cases demonstrated more advanced clinical stages and a male predominance, compared with API2-MALT1–negative cases. Thus, API2-MALT1–positive tumors should be cared for as a more aggressive subgroup and be followed for a longer time.