THE VALUE OF THE POLYMERASE CHAIN-REACTION IN THE DIAGNOSIS OF CUTANEOUS T-CELL INFILTRATES

The distinction between reactive and neoplastic cutaneous T-cell infil trates is difficult and requires good clinicopathologic correlation. M any cases manifest changes that are at the borderline between the two. The polymerase chain reaction (PCR) has been reported to detect monoc lonality in 52-90% of cutaneous T-cell lymphomas and may be of use in the diagnosis of histologically borderline lesions. We have investigat ed the use of PCR in a series of borderline lesions including borderli ne biopsy samples from patients who subsequently developed cutaneous l ymphoma. PCR amplification of T-cell receptor (TCR)-gamma chain gene w as performed on formalin-fu;ed, paraffin-embedded tissue from 27 cases of clinically and histologically typical mycosis fungoides (MF), 22 b orderline biopsy samples from 10 patients who subsequently developed M F (pre-MF), 32 clinically suspicious, histologically borderline lesion s, and 31 cases of chronic dermatitis. Monoclonality was demonstrated in 16 of 27 (59%) cases of MF, 10 of 22 (50%) pre-MF biopsy samples (s ix of 10 patients), and six of 32 (19%) borderline biopsy samples. The same size monoclonal band was detected in pre-MF biopsy samples from six of seven patients in which a band was demonstrated in the diagnost ic MF biopsy. Sequencing confirmed that the MF biopsy sample and the p re-MF biopsy sample contained the same clone. The 31 dermatitis cases gave rise to polyclonal PCR products. Monoclonality can be demonstrate d using PCR in 59% of MF cases, which is comparable with other T-cell lymphomas and in up to 50% of borderline biopsy samples in patients wh o later develop lymphoma. Detection of T-cell monoclonality by PCR is strong evidence of an established or evolving cutaneous T-cell lymphom a.