How useful are T-cell receptor gene rearrangement studies as an adjunct to the histopathologic diagnosis of mycosis fungoides?

The diagnosis and differential diagnosis of mycosis fungoides (MF) is often difficult, clinically and histologically. Recent attempts to enhance diagnostic sensitivity have involved T-cell receptor (TCR) gene rearrangement studies, using Southern blot or polymerase chain reaction (PCR) technique. PCR is more widely used because of its increased sensitivity, lower labor- and cost-intensive analytic steps, lack of radioactive substances, and applicability to routinely processed biopsies. Several studies that use this technique detect clonal bands in 50% to 83% of the MF specimens from patch, patch/plaque, and erythrodermic stages, which often pose a diagnostic challenge. This compares with no clonality in the control groups of most of these studies, or with up to 13% in a few studies, although long-term follow-up reveal that some cases of so-called "clonal dermatitis" eventually progress into overt cutaneous T-cell lymphoma. Furthermore, retrospective studies on archival histologic material from patients with MF demonstrate similar rates of clonality in histologically "inconclusive," "borderline," and diagnostic MF biopsies. Therefore, in the proper clinicopathologic setting, and with consideration of the known limitations of this technique, TCR gene rearrangement studies on lesional skin using PCR may be helpful as an adjunct to the histopathologic diagnosis of MF.