Multiple Immunoglobulin κ Gene Rearrangements within a Single Clone Unraveled by Next-Generation Sequencing–Based Clonality Assessment

Clonality assessment of the Ig heavy- and light-chain genes (IGH and IGK) using GeneScan analysis is an important supplemental assay in diagnostic testing for lymphoma. Occasionally cases with an IGK rearrangement pattern that cannot readily be assigned to a monoclonal lymphoma are encountered, whereas the occurrence of biclonal lymphomas is rare, and the result of the IGH locus of these cases is in line with monoclonality. Three such ambiguous cases were assessed for clonality using next-generation sequencing. Information on the sequences of the rearrangements, combined with knowledge of the complex organization of the IGK locus, pointed to two explanations that can attribute seemingly biclonal IGK rearrangements to a single clone. In two cases, this explanation involved inversion rearrangements on the IGK locus, whereas in the third case, the cross-reactivity of primers generated an additional clonal product. In conclusion, next-generation sequencing–based clonality assessment allows for the detection of both inversion rearrangements and the cross-reactivity of primers, and can therefore facilitate the interpretation of cases of lymphoma with complex IGK rearrangement patterns.