Posted September 1, 2011
Rick S. Bains, DO
Molecular techniques provide powerful tools that have drastically changed our understanding of entire categories of neoplasms, including lymphomas. T cell receptor gene rearrangement studies have had great success in the analysis of cutaneous T cell lymphomas (CTCL). Molecular techniques can offer great support for or against a diagnosis of lymphoma. However, it is important for clinicians and pathologists to be aware of their power and limitations in the evaluation of such lesions.
Clonality can be determined by evaluating rearrangements of the T cell receptor (TCR) genes, most commonly the beta or gamma genes. T cells typically undergo arrangement of both the TCR gamma gene followed by arrangement of the TCR beta gene. From a very early stage, all T lymphocytes undergo the process of T cell receptor gene rearrangement of the variable (V), diversity (D), and (J) joining segments to create a unique T cell receptor for each T cell. T cell receptor gene analysis is performed by amplification of multiple targets with multiplex polymerase chain reaction (PCR), followed by fragment analysis. In reactive processes several different T cells will be present and will result in a polyclonal pattern. However, T cell lymphomas are derived from a single T cell, and therefore a distinct clone will be identified.
The sensitivity of TCR gene analysis is based on data from the BIOMED-2 study, which standardized techniques in TCR gene rearrangement and is widely used by clinical molecular labs. The group’s data suggests the limit of detection of TCR analysis is roughly 10%1. The sensitivity of testing with regards to cutaneous T cell lymphomas has not been fully studied. However, recent studies suggest the sensitivity of PCR for T cell receptor gene rearrangements in CTCL may be lower than previously described2. This may be due in part to the low tumor burden in cutaneous lymphomas; and surrounding reactive lymphocytes can obscure TCR analysis.
TCR gene analysis can be extremely helpful, but it is important to be mindful of technical limitations3. Molecular labs usually evaluate clonality by analyzing either TCR gamma or TCR beta, or both. Very rarely will a T cell lymphoma have isolated gamma or beta rearrangement, but this may be a source of false negative results4. Evaluating both genes can provide increased sensitivity to the test; however, beta gene analysis is a more complex test and can be difficult to perform. Also, analysis can be performed on formalin-fixed tissue, but this causes fragmentation of the DNA and unreliable results. It is preferable to submit fresh tissue to ensure intact DNA.
Some clinically benign proliferations can have small clonal lymphocyte proliferations, such as CD8 and CD4 T-lymphocytosis or lymphomatoid papulosis1,5. Additionally, cases of parapsoriasis, pityriasis lichenoides, and lupus panniculitis have been reported as occasionally having monoclonality. Securing biopsies from different sites and/or at different times can strengthen findings by identifying the same clone6. Additionally, although rare in the skin, non-T cell processes can be positive for TCR gene rearrangement, making the correct diagnosis difficult. Because of these scenarios, it is important to interpret molecular results in the context of the clinicopathologic findings.
- van Dongen JJ, Langerak AW, Brüggemann M, Evans PA, Hummel M, Lavender FL, Delabesse E, Davi F, Schuuring E, García-Sanz R, van Krieken JH, Droese J, González D, Bastard C, White HE, Spaargaren M, González M, Parreira A, Smith JL, Morgan GJ, Kneba M, Macintyre EA. Design and standardization of PCR primers and protocols for detection of clonal immunoglobulin and T-cell receptor gene recombinations in suspect lymphoproliferations: report of the BIOMED-2 Concerted Action BMH4-CT98-3936. Leukemia. 2003;17(12):2257-317.
- Goeldel AL, Cornillet-Lefebvre P, Durlach A, Birembaut P, Bernard P, Nguyen P, Grange F. T-cell receptor gamma gene rearrangement in cutaneous T-cell lymphoma: comparative study of polymerase chain reaction with denaturing gradient gel electrophoresis and GeneScan analysis. Br J Dermatol. 2010;162(4):822-9.
- Groenen PJ, Langerak AW, van Dongen JJ, van Krieken JH. Pitfalls in TCR gene clonality testing: teaching cases. J Hematop. 2008;1(2):97-109.
- Brüggemann M, White H, Gaulard P, Garcia-Sanz R, Gameiro P, Oeschger S, Jasani B, Ott M, Delsol G, Orfao A, Tiemann M, Herbst H, Langerak AW, Spaargaren M, Moreau E, Groenen PJ, Sambade C, Foroni L, Carter GI, Hummel M, Bastard C, Davi F, Delfau-Larue MH, Kneba M, van Dongen JJ, Beldjord K, Molina TJ. Powerful strategy for polymerase chain reaction-based clonality assessment in T-cell malignancies Report of the BIOMED-2 Concerted Action BHM4 CT98-3936. Leukemia. 2007; 21(2):215-21.
- Langerak AW, Molina TJ, Lavender FL, Pearson D, Flohr T, Sambade C, Schuuring E, Al Saati T, van Dongen JJ, van Krieken JH. Polymerase chain reaction-based clonality testing in tissue samples with reactive lymphoproliferations: usefulness and pitfalls. A report of the BIOMED-2 Concerted Action BMH4-CT98-3936. Leukemia. 2007;21(2):222-9.
- Thurber SE, Zhang B, Kim YH et al. T-cell clonality analysis in biopsy specimens from two different skin sites shows high specificity in the diagnosis of patients with suggested mycosis fungoides. J Am Acad Dermatol. 2007; 57:782–90.
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