Multiple immunoglobulin kappa rearrangements within a single clone unraveled by NGS-based clonality assessment.

Abstract Clonality assessment of the immunoglobulin heavy (IGH) and light chain (IGK) using GeneScan analysis is an important supplementary assay in lymphoma diagnostics. Occasionally cases are encountered with an IGK rearrangement pattern that cannot readily be assigned to a monoclonal lymphoma, whereas the occurrence of bi-clonal lymphomas is rare and the result of the IGH locus of these cases is in line with monoclonality. We subjected three such ambiguous cases to next generation sequencing (NGS)-based clonality assessment. Sequence information of the rearrangements combined with knowledge of the complex organization of the IGK locus resulted in two explanations that can attribute seemingly bi-clonal IGK rearrangements to a single clone. For two cases, this involved inversion rearrangements on the IGK locus, whereas for the third case, cross-reactivity of primers generated an additional clonal product. In conclusion, NGS-based clonality assessment allows the detection of both inversion rearrangements and cross-reactivity of primers, and can therefore facilitate the interpretation of lymphoma cases with complex IGK rearrangement patterns.