p27^kip1 expression is inversely related to the grade of gastric MALT lymphoma

Background: Decreased or lost expression of the cyclin-dependent kinase inhibitor p27^kip1 protein has been found to be a poor prognostic factor in many cancers, including gastric cancer. Aim: To evaluate p27 ^kip1 expression in gastric mucosa-associated lymphoid tissue (MALT) and gastric B-cell lymphoma. Methods: Fifty-two cases of gastric lymphoma, mean age 68.7 yr (range 23-90 yr), 11 of chronic Helicobacter pylori-associated gastritis, and 5 of normal gastric mucosa were studied. Patients were classified into two groups. Stage IE gastric lymphomas were defined as local gastric lymphoma of MALT and more advanced stages as advanced gastric lymphoma. Twenty-three patients diagnosed as stage IE, 13 of these were low-grade and 10 diffuse large B-cell lymphoma (DLBL). Twenty-nine patients were at stage IIE or above, 18 with low-grade and 11 with DLBL. Serial sections were evaluated by immunohistochemistry after staining with antibodies against p27/Kip1 and Ki-67. Results: The proliferative index was higher in gastric DLBL than in low-grade MALT lymphomas, 57.1 ± 31.2 vs 17.3 ± 20.6 (p = 0.0001). The mean p27^kip1 expression score for high-grade patients was significantly lower compared with that of low-grade patients, 0.5 ± 0.4 and 1.6 ± 0.8, respectively (p = 0.001). Comparative evaluation of p27 ^kip1 expression in malignant lymphoid cells revealed that B cells of the localized gastric DLBL patients expressed the least p27^kip1, 0.36 ± 0.32. This value was lower than that of malignant lymphoid cells of patients with advanced DLBL, 0.64 ± 0.53, advanced low-grade MALT lymphoma, 1.59 ± 0.79, and localized low-grade MALT lymphoma, 1.59 ± 0.84. In the multivariate model in which all p27^kip1 variables were entered, the expression of p27^kip1 in malignant lymphoid cells was inversely correlated with the grade of the lymphoma irrespective of the stage of the disease (p = 0.0001), and significantly predicted grade: OR:0.07, 95% CI 0.07-0.31, p = 0.0001. Conclusion: p27 ^kip1 may be a putative distinct molecular marker to differentiate between low-grade and high-grade gastric lymphoma.