p27(Kip1) is detected on most gastric MALT lymphomas, but not large cell lymphomas.

We investigated the relationship of gastric mucosa-associated lymphoid tissue (MALT) lymphoma tumorigenesis to Helicobacter pylori infection, the t (11;18) translocation, and alterations in cell cycle regulators. We sought to assess the implications of altered expression of p27(Kip1), a cyclin-dependent kinase inhibitor, on high-grade transformation and responsiveness to eradication therapy. We used immunohistochemistry to examine p27(Kip1), p53, and Ki-67 expression in 23 MALT lymphomas, five diffuse large B-cell lymphomas (DLBCLs), and four DLBCLs with associated MALT lymphoma. All of the MALT lymphomas were positive for p27(Kip1) expression and negative for p53 with a low Ki-67 index, regardless of the sensitivity of these cells to eradication. All DLBCLs were negative for p27(Kip1) and positive for p53, exhibiting a high Ki-67 index. In DLBCLs with MALT lymphoma, p27(Kip1) expression was absent from both the MALT and large cells components. In all of these lymphomas, the MALT components were negative for p53 and displayed a low Ki-67 index, while the large cell components were positive for p53 with a high Ki-67 index. The expression patterns of the DLBCLs differed significantly from those of the MALT lymphomas. p27(Kip1) was not detected in either component of DLBCL with MALT lymphoma, suggesting that decreased expression of p27(Kip1) in the MALT component may be related to high-grade transformation. Thus, p27(Kip1) expression in morphological MALT lymphomas could be useful tool to predict high-grade transformation to DLBCL.