RESUMO
Background: Clonality assessment is currently the major molecular analysis utilized to support the diagnosis of suspicious lymphoid malignancies. Clonal rearrangements of the V-J segments of T-cell receptor G chain locus (TCRγ or TRG) have been observed in almost all types of T neoplasms, such as T-cell-related non-Hodgkin lymphomas and leukemias. At present, the gold standard for clonality evaluation is multiplex polymerase chain reaction (PCR), plus subsequent capillary electrophoresis/heteroduplex analyses, and/or Sanger sequencing. This approach overcomes the problem with the conventional Southern blot hybridization and is more efficient, simple, fast, and reproducible. In the recent years, the new next-generation sequencing (NGS) technologies provided alternative techniques for the analysis of antigen receptors genes, which presented several advantages, such as increased efficiency, specificity (SP), sensitivity (ST), resolution, and objectivity of the results, leading to a better classification, stratification, and monitoring of lymphoid malignancies. Nonetheless, these technologies are still far from being the new gold standard since further studies are warranted to prove their utility. The present study aimed to assess the diagnostic accuracy of these two methods by comparing a commercial NGS-based assay for the evaluation of TRG locus with the gold standard PCR-based one, to fulfill the requirements of a phase 3 diagnostic accuracy study. Methods: We assessed the TRG gene rearrangements in 72 cases using the conventional and highly-validated PCR-based assay proposed by EuroClonality consortium, an alternative commercial PCR-based assay, namely, IdentiClone® TCR Gamma Gene Rearrangement Assay 2.0, and a commercial NGS-based assay, that is, Invivoscribe LymphoTrack® Dx MiSeq® (both by Invivoscribe Technologies Inc., San Diego, CA, USA), to determine the diagnostic accuracy of the latter, and compare them with reference diagnoses made based on observation of clinical manifestations, cytohistological, and immunohistochemical analyses. Statistical values were calculated using the Oxford CATmaker software package. Results: Using standardized criteria of interpretation, the obtained results showed a diagnostic accuracy of 90.3% (correspondence in 65 out of 72 cases) of the test under investigation, with a ST of 86%, a SP of 95%, a positive predicting value of 94%, and a negative predicting value of 88%, demonstrating that it had high efficiency and reliability in detecting clonal TRG gene rearrangements in T-cell non-Hodgkin lymphomas. Conclusions: This diagnostic accuracy study yielded comparable results using a validated PCR-based approach and a new NGS-based one. Subsequent studies and cost-effectiveness evaluation are needed to put the NGS-based clonality assessment into routine diagnostic practice.
RESUMO
BACKGROUND: Multiplex PCR based on consensus primers followed by capillary electrophoresis and Sanger sequencing are considered as the gold standard method for the evaluation of clonality and somatic hypermutation in lymphoid malignancies. As an alternative, the next-generation sequencing (NGS) of immune receptor genes has recently been proposed as a solution, due to being highly effective and sensitive. Here, we designed a phase III diagnostic accuracy study intended to compare the current gold standard methods versus the first commercially available NGS approaches for testing immunoglobulin heavy chain gene rearrangements. METHODS: We assessed IGH rearrangements in 68 samples by means of both the NGS approach (LymphoTrack® IGH assay, and LymphoTrack® IGH somatic hypermutation assay, run on Illumina MiSeq) and capillary electrophoresis/Sanger sequencing to assess clonality and somatic hypermutations (SHM). RESULTS: In comparison to the routine capillary-based analysis, the NGS clonality assay had an overall diagnostic accuracy of 96% (63/66 cases). Other studied criteria included sensitivity (95%), specificity (100%), positive predictive value (100%) and negative predictive value (75%). In discrepant cases, the NGS results were confirmed by a different set of primers that provided coverage of the IGH leader sequence. Furthermore, there was excellent agreement of the SHM determination with both the LymphoTrack® FR1 and leader assays when compared to the Sanger sequencing analysis (84%), with NGS able to assess the SHM rate even in cases where the conventional approach failed. CONCLUSION: Overall, conventional Sanger sequencing and next-generation-sequencing-based clonality and somatic hypermutation analyses gave comparable results. For future use in a routine diagnostic workflow, NGS-based approaches should be evaluated prospectively and an analysis of cost-effectiveness should be performed.