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T-CELL CLONALITY BY PCR REFLEX TO TCR-BETA (TRB) REARRANGEMENTS, NON-BLOOD

Test Code: BMTCLO
Description: T-Cell Clonality TCR gamma gene (TRG) rearrangements occur early in T-cell ontogeny and are unique to each T-cell. TCR- beta (TRB) rearrangements occur later in ontogeny and also serve as a marker for clonality. The Stanford Molecular Genetic Pathology Laboratory has 2 algorithms integrating TRG and TRB testing depending on the pre-test probability of disease – see Figure and explanation below (Zhang et al, J Molec Diag, 2010). This test is useful for determining whether a clonal population of T-cells is present in a specimen (blood, tissue, fluid or paraffin block). The T-cell clonality assay by Next Generation Sequencing (NGS) establishes whether a clonal population of T-cells is present in a diagnostic specimen. Clonality studies should be interpreted in light of available clinical and pathologic information. It is important to note that identification of a clonal cell population is not by itself diagnostic of malignancy. This test is useful for diagnosis and monitoring of T-cell malignancies.

The laboratory offers two suggested algorithms for interpretation of T-cell clonality testing. The TCR-LR algorithm is designed for cases in which the clinician's pre-test estimate of the probability of lymphoma is low-to-moderate (approx. 0.15 – 0.5). Following this algorithm, if the initial TRG test is negative the TRB testing is not performed and the result is interpreted as no clonal support (algorithm above). If the TRG test is positive in a low-to-moderate risk patient, the TRB testing is performed. If both the TRG and TRB testing are positive in the low-to-moderate risk patient, the result is interpreted as clonal support for lymphoma. If the TRG is positive but the TRB is negative in a low-to-moderate risk patient, the result is interpreted as non-diagnostic and repeat testing is recommended.

The second algorithm (TCR-HR) is designed for cases in which the clinician's pre-test estimate of lymphoma is moderate-to-high (approx. 0.5 – 0.75). Following the TCR-HR algorithm, if the initial TRG testing is positive, the TRB testing is not performed and the result is interpreted as clonal support for MF. If the initial TRG testing is negative in a moderate-to-high risk patient, TRB testing is performed. If the TRB test is positive in a moderate-to-high risk patient, it is interpreted as clonal support for MF. If both the TRG and TRB tests are negative in a moderate-to-high risk patient, the result is interpreted as no clonal support for lymphoma. These two diagnostic algorithms are designed to utilize clinical information to improve the overall accuracy of clonality testing. In choosing the TCR testing algorithm for a patient of moderate risk of lymphoma, clinicians should consider that the TCR-LR algorithm will result in higher specificity (with some loss of sensitivity), while the TCR-HR test will result in higher sensitivity with some loss of specificity.


 
 


 
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