BIOMED-2 PCR assays for IGK gene rearrangements are essential for B-cell clonality analysis in follicular lymphoma.

B-cell clonality analysis is commonly performed by polymerase chain reaction (PCR) targeting the IGH genes although a high false-negative rate is recognized for germinal centre/post-germinal centre B-cell malignancies, especially follicular lymphoma. We assessed the diagnostic value of BIOMED-2 IGK assays and investigated the cause of IGH PCR failure in 77 patients with follicular lymphoma. Using the full set of BIOMED-2 reactions, clonal immunoglobulin gene rearrangements were detected in 74 (96%) cases. The clonality detection rate was 86% by two IGK reactions but only 68% by five IGH reactions (P < 0·001). Sequencing of the clonal PCR products showed significantly fewer somatic mutations in the rearranged IGKV (9/27 cases, 33%, mean mutation rate 0·5%) than IGHV (17/17 cases, 100%, rate 11·0%) (P < 0·01). All IGHV-IGHJ PCR failures occurred in cases with at least one mutation at the corresponding IGHV primer binding sites. t(14:18)(q32:q21)/IGH-BCL2 was detected in 50 of 71 (70%) cases and the presence of the translocation was not associated with the poor performance of IGH assays. Our results showed that BIOMED-2 IGK assays are significantly more sensitive than IGH assays in follicular lymphoma due to the fact that the rearranged IGKV is less frequently targeted by somatic hypermutation than IGHV, and therefore, are essential in routine clonality analysis of these lymphomas.