The added value of immunoglobulin Kappa light chain gene (IGK) rearrangement analysis in suspected B-cell lymphomas: three illustrative cases

Immunoglobulin Kappa light chain gene (IGK) rearrangements are important complementary PCR targets for clonality assessment in mature B-cell proliferations in which detection of clonal VH-JH gene rearrangements fails. Failure to amplify VH-JH rearrangements is mainly attributable to somatic hypermutation. Detection of clonal IGK rearrangements is most relevant in the diagnosis of germinal center (GC) and post-GC B-cell lymphomas that are under a heavy somatic mutation process. Here we present three cases in which histology and immunophenotype of the tissue samples at time of diagnosis were inconclusive. PCR-based B-cell clonality assessment was performed using the standardized BIOMED-2 multiplex PCR protocols and Genescan analysis. No clonal VH-JH rearrangements were observed. Detection of a clonal IGK product in each of the three suspected cases supported the clonal origin of the B-cell proliferations. Interestingly, only rearrangements involving the Kde element were detected. Based in the clonal IGK-PCR result, a definitive diagnosis of follicular lymphoma (case 1 and 3) and extranodal marginal zone lymphoma (case 2) was established.