The utility of the in situ detection of T-cell receptor Beta rearrangements in cutaneous T-cell-dominant infiltrates.

The diagnostic assessment of cutaneous T-cell infiltrates is problematic for dermatopathologists. A variety of conditions, including lymphomatoid hypersensitivity reactions and lymphomatoid lupus erythematosus, can demonstrate lymphoid atypia and phenotypic changes that can mimic cutaneous T-cell lymphoma (CTCL). A similar issue revolves around lymphoid dyscrasias, which includes parapsoriasis, atypical pigmentary purpura, pityriasis lichenoides chronica, indeterminate lymphocytic lobular panniculitis, and lymphomatoid papulosis, which can progress to CTCL. A reverse transcription (RT) in situ PCR assay for T-cell receptor beta rearrangements (TCRbeta) was used to assess T-cell clonality in formalin-fixed, paraffin-embedded tissues. In 7 of 8 cases of classic CTCL, the RT in situ PCR assay for TCRbeta rearrangement showed monoclonality; the other was biclonal. Further, in cases with multiple lesions over time, the same T-cell clone could be detected including in those patients whose biopsies showed large-cell transformation. Monoclonality was also demonstrated in each of 2 cases of cutaneous lymphomatoid papulosis. Demonstration of oligoclonality (and one case of biclonality) by RT in situ PCR was confined to those cases that either represented prelymphomatous conditions such as large plaque parapsoriasis or pityriasis lichenoides or lesions of drug-induced lymphomatoid hypersensitivity that all demonstrated clinical regression. In conclusion, RT in situ PCR for TCRbeta, which can be done on formalin-fixed biopsies and allows direct correlation of the molecular data with the histology, is a useful adjunctive test in the differentiation of CTCL from its mimics.