Clonal antigen receptor gene PCR products outside the expected size range

Polymerase chain reaction (PCR) of the antigen receptor genes has clinical utility in establishing clonality in lymphoproliferations, which is an important correlate of lymphoid neoplasia. The most frequently used procedures for this purpose were developed by the BIOMED-2 consortium. One of the criteria for establishing monoclonality using PCR of the antigen receptor genes is the finding of an abundant amplicon within a size range determined by the positions of the PCR primers and the known variability in size inherent in the recombination events that assemble a functional antigen receptor gene. However, several cases have been reported in which an amplicon outside this size range has been shown to be a valid indicator of clonality after DNA sequence analysis. In this paper, we will report and discuss several additional cases in which an amplicon outside the accepted size range was consistent with a monoclonal lymphoproliferation. We conclude that oversized and undersized amplicons may indeed represent evidence for a monoclonal lymphoproliferation, but that this interpretation should preferably be confirmed by sequence analysis to avoid a false-positive result.