Lymph nodes in gastric B-cell lymphoma: Pattern of involvement and early histological changes

Aims: This study aims to analyse the histological pattern of nodal involvement in gastric B-cell lymphoma and to detect early involvement of the lymph nodes. Methods and results: Histological findings of 37 resected primary gastric lymphomas with 1313 regional lymph nodes were analysed. The primary tumour was classified into four groups: MALT lymphoma, MALT lymphoma with a minor large B-cell lymphoma (<20%), large B-cell lymphoma with MALT lymphoma, and large B-cell lymphoma without MALT lymphoma. Histological patterns of nodal involvement were divided into sinusoidal, subsinusoidal/marginal, follicular, and diffuse patterns. Seminested polymerase chain reaction (PCR) analysis for IgH gene rearrangement was performed. Nodal involvement was found in 2/13 (15%) MALT lymphomas, 5/6 (83%) MALT lymphomas with a minor large B-cell lymphoma, 9/12 (75%) large B-cell lymphomas with MALT lymphoma, and 6/6 (100%) large B-cell lymphomas without MALT lymphoma. The MALT lymphoma and MALT lymphoma with a minor large B-cell lymphoma showed a predominantly sinusoidal and subsinusoidal pattern, whereas diffuse pattern predominated in large B-cell lymphomas without MALT lymphoma and large B-cell lymphomas with MALT lymphoma. The follicular pattern was least common, being observed in 10.2% of large B-cell lymphomas without MALT lymphoma and large B-cell lymphomas with MALT lymphoma. Sinusoidal obliteration with permeation of small monocytoid cells into subsinusoidal zone is a characteristic finding suggesting early nodal involvement of MALT lymphoma. Conclusions: Histological patterns of nodal involvement in gastric B-cell lymphoma vary according to the histological grade. Immunostaining for CD20 with or without PCR analysis for IgH gene rearrangement would be a useful ancillary method to confirm lymphomatous involvement.