RESUMEN
<p><b>OBJECTIVE</b>To study the morphologic and immunohistochemical features of gastrointestinal B-cell lymphomas.</p><p><b>METHODS</b>One hundred and ninety-four cases of gastrointestinal B-cell lymphoma were retrieved from the archival file. The clinical features and pathologic findings were reviewed. Immunohistochemical study for B-cell markers, T-cell markers, bcl-6, CD10, bcl-10, cyclin D1, TdT, MUM1 and Ki-67 was carried out.</p><p><b>RESULTS</b>The male-to-female ratio was 1.4:1. The age of patients ranged from 8 to 85 years. Amongst the 194 cases studied, 128 (66.0%) were diagnosed as diffuse large B-cell lymphoma, including 16 cases of large cell lymphoma associated with mucosa-associated lymphoid tissue (MALT) lymphoma component. There were also 40 cases (20.6%) of MALT lymphoma, 8 cases (4.1%) of follicular lymphoma, 5 cases of (2.6%) of lymphoplasmacytic lymphoma, 3 cases (1.6%) of mantle cell lymphoma, 1 case of (0.5%) of B-lymphoblastic lymphoma and 9 cases (4.6%) of indefinite type (including 5 biopsy cases). The site of involvement included stomach (100 cases, 51.5%), small intestine (43 cases, 22.2%), ileocecal junction (26 cases, 13.4%), appendix (1 case, 0.5%), colon (21 cases, 10.8%) and rectum (3 cases, 1.6%). Amongst the 163 cases which had undergone surgical resection, 20 cases (12.3%) cases had invasion down to the mucosa, 20 cases (12.3%) down to the superficial muscular layer, 19 cases (11.6%) down to the deep muscular layer and 104 cases (63.8%) with full-thickness involvement. Histologic examination showed lymphoepithelial lesions in 52 cases, residual lymphoid follicles in 29 cases, coagulative necrosis in 66 cases and nodular growth pattern in 30 cases. The lymphoma cells in all cases were immunoreactive for B-cell marker CD20. There was also various degrees of positivity for bcl-6, CD10, bcl-10, cyclin D1, TdT, MUM1 and Ki-67.</p><p><b>CONCLUSIONS</b>Gastrointestinal B-cell lymphomas can be subdivided into two main groups: large B-cell lymphomas and small B-cell lymphomas. The latter group often poses diagnostic pitfalls. Accurate pathologic typing requires correlation with histologic and immunohistochemical findings.</p>