Primary gastric lymphomas (MALTomas): a nuclear image analysis comparison with lymph node monocytoid B-cells and marginal zones of spleen and Peyer's patches

Centrocyte-like cells of marginal zones of follicles of gastrointestinal lymphoid tissue, which have their analogous in marginal zone of splenic white pulp and in lymph node monocytoid B-lymphocytes, are thought to be the normal counterpart of lymphomas of MALT (MALTomas). However, the cell population of MALTomas is often polymorphic and also contains cells morphologically different from centrocytes. Since conventional morphologic analysis may not be accurate enough and the phenotype may change in different stages of B-cell lineage, the marginal zone of Peyer's patches (PMZ) and splenic white pulp (SMZ), the lymph node monocytoid B-lymphocytes (ML), 3 nodal monocytoid B-cell lymphomas (L) and 16 gastric MALTomas (M) were studied by means of automated nuclear image analysis for area, irregularity, and chromatin texture assessment. Immunophenotyping on paraffin sections and polymerase chain reaction (PCR) for detecting monoclonality and t(14-18) chromosome breakpoints at DNA levels, on paraffin section extractions, were also done. In 14 MALTomas, clonal Ig heavy chain rearrangement was detected and in none of these were found t(14-18) chromosome breakpoints. The nuclei of the control group (PMZ, SMZ and ML) showed the same morphologic characteristics, ie. size, irregularity, chromatin texture. MALTomas and nodal lymphomas were distributed into 3 clusters: (1) with larger nuclei, light chromatin (euchromatin-richer) (5 MALTomas, 2 nodal lymphomas together with the control group); (2) nuclei with the same area size, but darker (eterochromatin-richer) (6 MALTomas and 1 nodal lymphoma); (3) with smaller and darker nuclei (5 MALTomas). Chromatin textural differences were maintained in the same nuclear size class in the 3 clusters. Only a few MALTomas had nuclear features not significantly different from controls, inter-case and intra-case variability being evident.