In Situ Hybridization Analysis of Lymphoproliferative Disorders: Assessment of Clonality by Immunoglobulin Light-Chain Messenger RNA Expression

Determination of clonality in B-cell lymphomas is a useful diagnostic adjunct. In situ hybridization (ISH) for the detection of K and Λ mRN As has the potential to overcome some common specimen-related limitations in clonal assessment. Tritium-labeled antisense cRNA probes directed at conserved segments of the constant regions of the kappa and lambda mRNAs were used in an autoradiographic method to detect B-cell clonality. Using these probes, we analyzed 103 formalin-fixed, paraffin-embedded biopsy samples, and the results were subsequently compared to available immunophenotypic (all cases) and genotypic (50 cases) data. Of 103 samples, 82 (80%) had adequate RNA preservation as determined by actin RNA signals, and 73 (89%) of the 82 cases demonstrated concordant clonality assignment by both ISH and immunophenotyping. The remaining nine cases showed a specific form of discordance in that each exhibited no protein (Ig) expression but had evidence of mRNA immunoglobulin light-chain expression. Forty-five (90%) of 50 cases evaluated for immunoglobulin and T-cell receptor β-gene rearrangements demonstrated concordant results with respect to clonality assignment by ISH. Thus, ISH demonstrates adequate sensitivity with respect to traditional methods of clonality assessment. However, its practical utility awaits the development of nonradioactive detection methods with adequate sensitivity to improve turnaround time.