Clonal T-cell receptor γ-chain gene rearrangement by PCR-based GeneScan analysis in advanced cutaneous T-cell lymphoma: a critical evaluation

Detection of clonal T-cell receptor γ (TCRγ)-chain gene rearrangement is a promising approach to distinguish between cutaneous T-cell lymphomas (CTCLs) and reactive T-cell infiltrates. Despite the improved sensitivity by using the polymerase chain reaction (PCR) rather than Southern blot analysis, monoclonality could be demonstrated in only 53–90 per cent of CTCL biopsies in recent studies. In the present study, formalin-fixed, paraffin-embedded specimens of 21 selected patients with clear-cut advanced-stage CTCL were analysed using a semi-nested TCRγ PCR with newly developed consensus primer pairs. Detection of PCR products was done by GeneScan analysis (GSA); this technique is advantageous due to its sensitivity and accuracy in the detection and size determination of PCR products and it is easier to interpret than direct read-outs from TGGE or DGGE gels. In serial dilution experiments, TCRγ-PCR-GSA allowed the detection of clonal, rearranged T-cells with a high in vitro sensitivity against a polyclonal background (1–6 per cent). Despite the selection of clear-cut, advanced-stage CTCL cases, however, dominant clonal TCRγ-chain gene rearrangement was found in only 16 of the 21 patients analysed, indicating an overall clinical sensitivity of 76 per cent. Specificity was evaluated using biopsy specimens from 21 control patients suffering from long-standing psoriasis (n = 13) and eczema (n = 8). Surprisingly, GeneScan profiles showing apparently single dominant peaks were detected in 14 per cent of these skin lesions, but these profiles turned out to be pseudo-monoclonal by repeated determinations. In conclusion, TCRγ-PCR-GSA does not suffice reliably to exclude malignancy, due to its limited clinical sensitivity, but with precautions taken to detect pseudo-monoclonality and to secure specificity, TCRγ-PCR-GSA is a valuable instrument in the diagnosis of CTCL. Copyright © 1999 John Wiley & Sons, Ltd.