B-cell and T-cell Clonality Assays by PCR

Quest Diagnostics offers 7 test codes for lymphoid clonality studies.

For T-cell lymphomas:

• 90509 T-cell Receptor (TCR) Gamma Gene Rearrangement, PCR
• 91446 T-cell Receptor (TCR) Beta Gene Rearrangement, PCR
• 91445 T-cell Clonality Panel (TCRG, TCRB), PCR

For B-cell lymphomas:

• 90362 B-cell Receptor IGH Gene Rearrangement, PCR
• 90363 B-cell Receptor IGK Gene Rearrangement, PCR
• 91635 B-cell Clonality Panel (IGH, IGK), PCR

For mixed B-cell and T-cell infiltrates or for lymphomas of unclear lineage:

• 91634 Lymphocyte Clonality Panel, PCR; includes IGH, IGK, TCRG and TCRB

All 7 test codes include a pathologist’s integrated interpretation.

The TCR-gamma gene rearrangement PCR (test code 90509) is the preferred assay for T-cell clonality determination. However, false-positives can occur in samples with many reactive gamma-delta T-cells.

Use of the panel, which includes analysis for TCRG and TCRB gene rearrangements, can help avoid over-diagnosis of T-cell clonality in skin biopsies, spleen, and blood.¹ Combining analysis for TCRG and TCRB gene rearrangements can also improve the diagnostic sensitivity compared to either TCRG or TCRB gene rearrangements alone in up to 10% of cases.² In a multicenter study from the BIOMED-2 group, all definitive cases of T-cell lymphomas and leukemias (including T-PLL, T-LGL, and PTCL) showed clonal TCRB and/or TCRG gene rearrangements.²

The TCR-beta gene rearrangement PCR (test code 91446) should only be ordered as a stand-alone test if a prior TCR-gamma gene rearrangement result is inconclusive or inconsistent morphologically or clinically, and additional testing is desired.

The B-cell receptor IGH gene rearrangement PCR (test code 90362) is the preferred assay for B-cell clonality determination.

However, false-negative results are seen in the IGH PCR assay in 5% to 20% of B-cell lymphoproliferative neoplasms due to intrinsic biologic mechanisms. These include absent or incomplete IGH rearrangements in immature B-cell neoplasms, such as lymphoblastic leukemia/lymphoma, and the presence of extensive somatic mutation in some mature B-cell lymphoma, particularly follicular lymphoma and plasma cell neoplasms. The combination of IGH and IGK PCR can overcome these limitations and detect a clonal rearrangement in up to 99% of B-cell neoplasms.³ The B-cell clonality panel is thus recommended for lymphoblastic neoplasms and in suspected follicular lymphoma. Dual IGH and IGK testing can also help to distinguish oligoclonal rearrangements patterns from true monoclonal B-cell infiltrates.¹

The B-cell receptor IGK gene rearrangement PCR (test code 90363) should only be ordered as a stand-alone test if a prior IGH result is inconclusive or inconsistent morphologically or clinically, and additional testing is desired. The IGK gene rearrangement assay is also useful in determining clonality in lymphoblastic leukemia/l lymphoma.

Immature lymphoid neoplasms such as acute lymphoblastic leukemia/lymphoma (ALL/LBL) often lack complete IGH, IGK, TCRG, and TCRB rearrangements⁴ or can have a bilineal or mixed immunophenotype. Therefore, clonality determination in ALL/LBL often requires several PCR assays to identify a detectable rearrangement that can be used for diagnosis and follow up.

Mixed B-cell and T-cell infiltrates are also commonly encountered. They are particularly common in skin lesions in which it is not clear whether the lesion represents a B-cell lymphoma, a T-cell lymphoma, or a mixed reactive proliferation. Finally, composite B-cell and T-cell lymphomas can occur, especially when atypical T-cell and EBV+ B-cell infiltrates are identified by immunohistochemistry. In these cases, a full lymphoid clonality PCR panel may be a useful adjunct to diagnosis.

The following samples can be submitted for all of these PCR assays:

• Peripheral blood or bone marrow aspirate (do not freeze)
• Fine needle aspirate material, in an alcohol-based fixative
• Formalin-fixed paraffin-embedded (FFPE) sections or tissue blocks
• Fresh-frozen tissues shipped on dry ice

See test description in our online Test Center for minimal sample requirements.

No. TCR-gamma gene rearrangements are present in both TCR-a/b+ and TCR-g/d+ T-cell lymphoproliferative disorders and are not necessarily indicative of gamma/delta lineage.

Pathology reports are critical, especially for FFPE samples, for matching the sample number and for information about the sample source, type of specimen, and, when available, the T-cell and B-cell proportions from immunostain results. Interpretation of PCR-based lymphoid assays is complex and impacted by these factors.

If no final pathology report is available, a preliminary report showing the sample number and specimen source is acceptable.