ASSESSMENT OF CLONALITY IN CUTANEOUS LYMPHOID INFILTRATES BY POLYMERASE CHAIN-REACTION ANALYSIS OF IMMUNOGLOBULIN HEAVY-CHAIN GENE REARRANGEMENT

Determination of the biologic potential of cutaneous lymphoid infiltra tes may be difficult by standard histologic or immunohistologic examin ation. The polymerase chain reaction (PCR) has been used to document c lonal rearrangements of the immunoglobulin heavy chain gene in paraffi n-embedded fixed tissues. To explore the value of PCR in evaluation of cutaneous lymphoid infiltrates, 93 archival nonmycotic lymphoid lesio ns (28 small or mixed lymphocytic lymphomas, 15 large cell lymphomas, 40 benign infiltrates, and 10 with atypical features) were analyzed. T hese cases had been previously immunophenotyped on paraffin sections, and clinical follow-up from 7 to 20 years was gathered. DNA products w ere generated using a seminested PCR technique, separated by 5% polyac rylamide gel elec trophoresis, stained with ethidium bromide, and visu alized under UV light Cases with a 100- to 120-base pair band were sco red as positive. Of the 28 small or mixed cell lymphomas, 23 had a B-c ell immunophenotype or consisted of a mixture of B and T cells; of the se, seven (30%) demonstrated a monoclonal pattern, and three (13%) wer e indeterminate. Twelve large cell cases were B-cell or mixed; five (4 2%) of these were positive for a monoclonal band, while four (33%) wer e indeterminate. None of five T-cell small cell or three T-cell large cell lymphomas demonstrated a monoclonal band. In contrast, 39 of the 40 benign cases were T-cell predominant or mixed lesions. Nevertheless , 18 of these 40 cases on initial testing suggested possible monoclona lity. Six were indeterminate, and 12 demonstrated apparent monoclonal bands, of which four were reproducible on repeat testing. No histologi c or clinical features of lymphoma were present in 17 of these 18 case s, suggesting that they represent false-positive results. Most of the latter lesions showed sparse perivascular infiltrates, with very few B cells. This suggests that amplification of the immunoglobulin heavy c hain gene from a small number of lymphocytes may produce a monoclonal band. In summary, PCR may provide adjunct information about clonality in selected lymphoid skin lesions, but is rather insensitive in this s etting. Such data must be carefully considered in the context of the h istologic, immunohistologic, and clinical findings, particularly when assessing sparse infiltrates, because of the potential for false-posit ive results.