New insights into the applicability of T-cell receptor γ gene rearrangement analysis in cutaneous T-cell lymphoma

Background: Detection of clonal T-cell receptor (TCR) gamma gene rearrangement by polymerase chain reaction (PCR) based method is a marker for cutaneous T-cell lymphoma (CTCL) although it can be seen in some benign dermatoses. To determine the accuracy of histologic criteria alone as well as the adjuvant diagnostic role of TCR gene rearrangement for the diagnosis of CTCL, we studied 100 patients with cutaneous T-cell infiltrates by both histology and TCR gene rearrangement. Methods: The histologic features of the 100 patients were first reviewed by two independent dermatopathologists and their confidence in the diagnosis of CTCL was assigned one of four levels. Then the specimens were analyzed for TCR gene rearrangement either on paraffin-embedded or fresh-frozen tissue by PCR/denaturing gradient gel electrophoresis (DGGE). Results: The clonality was detected in 100% (15/15) diagnostic of, 84.6% (11/13) consistent with, 57.6% (19/33) suggestive of CTCL. In 9 cases TCR gene rearrangement was compared between formalin-fixed and fresh specimens of the same individual, but with different degrees of histologic confidence (no lower than suggestive). In all cases fresh specimens were positive. In 5 of the cases (2-diagnostic, 2-consistent, 1-suggestive) formalin-fixed specimens were positive as well, and in 4 cases (1-consistent, 3-suggestive) formalin-fixed specimens were negative. When TCR gene rearrangement was studied in eight cases on sequential biopsies from the same patient, the clonality was detected in only one or two biopsies in four cases in which the histologic confidence was low (suggestive or nondiagnostic). The TCR gene rearrangement study showed identical banding patterns in lesions from different clinical stages in most patients. However, we observed that in one case, oligoclonal-banding pattern was seen in initial biopsy with histopathologic consistent with CTCL, while monoclonal banding pattern in more advanced lesion. Conclusions: Our data have demonstrated that TCR gene rearrangement studies by PCR/DGGE are consistently positive regardless of tissue fixation (formalin-fixed, paraffin-embedded vs. fresh-frozen tissue) and biopsy site when the histologic degree of confidence is very high (diagnostic). So, it may be of less importance as an adjuvant to histopathologic diagnosis for the cases with diagnostic CTCL histology. However, TCR gene rearrangement studies are particularly important in earlier cases with less conclusive histology, which provides strong confirmatory evidence of an evolving CTCL. In these cases, multiple biopsies may be required to establish the diagnosis and analysis of fresh tissue is suggested to increases the sensitivity. Moreover, our observation also suggested that some CTCL might not be monoclonal de novo, but oligoclonal instead.