Clinicopathologic Comparison between the API2‐MALT1 Chimeric Transcript‐positive and ‐negative Gastric Low‐grade B‐Cell Lymphoma of Mucosa‐associated Lymphoid Tissue Type

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Abstract
Little is known about the clinicopathological differences between API2‐MALT1 chimeric transcript‐positive and ‐negative gastric low‐grade B‐cell lymphomas of mucosa‐associated lymphoid tissue (MALT) type. The aim of this study was to clarify those differences in gastric MALT lymphoma. Twenty‐three patients with gastric MALT lymphoma were enrolled in a unicenter study. Helicobacter pylori (H. pylori) infection status and clinical stages were investigated. Antibacterial treatment was performed for every patient. Responsiveness of MALT lymphoma to this treatment was assessed by means of regular follow‐up endoscopy combined with biopsy. All cases were examined for API2‐MALT1 chimeric transcript by means of RT‐PCR and sequencing analyses. H. pylori infection status was assessed as positive in 20 patients and negative in three. With regard to responsiveness to antibacterial treatment, complete remission was observed in two patients, partial remission in 12 and no change in nine. API2‐MALT1 chimeric transcript was detected in seven patients, all of whom showed no change in response to antibacterial treatment. API2‐MALT1 positivity was found to be significantly correlated with responsiveness to antibacterial treatment (P=0.0001), absence of H. pylori infection (P=0.0198), and gross cobblestone mucosa observed endoscopically (P=0.0198). For the other factors (age, sex, dominant site of lesion, high‐grade component, infiltrated layer of gastric wall, nodal involvement or clinical stages), there were no differences between API2‐MALT1 chimeric transcript‐positive and ‐negative cases. Gastric API2‐MALT1 chimeric transcript‐positive MALT lymphoma generally features unresponsiveness to antibacterial treatment, and is thought to be unrelated to H. pylori infection in its pathogenesis. Our findings indicate the presence of different clinical subtypes in gastric MALT lymphomas.

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