Gain of chromosome 7, which marks the progression from indolent to aggressive follicle centre lymphomas, is restricted to the B-lymphoid cell lineage: a study by FISH in combination with morphology and immunocytochemistry

In a previous fluorescent in situ hybridization (FISH) study of patients wi th high-grade follicle centre lymphomas (FLCs), we often found additional c opies of chromosome 7 in bone marrow (BM) cell nuclei even though obvious m alignant tumour cells could not always be morphologically identified in the corresponding cell smears. This raised the question whether the gains of c hromosome 7 are really confined to B-lymphoid tumour cells or whether other cell lineages are also of clonal origin. In the present investigation we e mployed FISH in combination with immunomarkers and morphological studies on BM smears and lymph node imprints from seven patients with high-grade FCLs and diffuse large B-cell lymphomas (DLBCLs). Three out of seven BM samples were found to contain clonal CD20-positive B-lymphoid cells (range 0.4-96% of the cells) and no extra copies of chromosome 7 were detected in the mye lomonocytoid or erythroid cells or in the CD3-positive T lymphocytes. All s even patients showed additional copies of chromosome 7 in the lymph nodes a nd, again, this cytogenetic abnormality was also restricted to the CD20-pos itive cells (range 0.7-80% of the cells). Thus the present findings confirm that high-grade B-cell lymphomas with Or without RM engagement involve the CD20-positive B-lymphoid cells exclusively and not the T lymphocytes, eryt hroid or myelomonocytoid cell lineages. These findings may indicate that an ti-CD20 immunotherapy could be of value in high-grade B-cell lymphomas.