Detection of monoclonal lymphoid cell populations by polymerase chain reaction technology.

Molecular studies have substantially broadened our understanding of cutaneous lymphoproliferative disorders and have been introduced in the routine assessment of lesions suggestive of a lymphoma. As compared with traditional Southern blot analyses, PCR-based assays for the detection of monoclonal lymphoid populations in clinical specimens offer several advantages. In general, they are faster to perform and allow for the detailed molecular analysis of very small tissue specimens, including sections from formalin-fixed, paraffin-embedded biopsy specimens. The PCR-based assays for the analysis of CTCL involve the amplification of highly variable junctional sequences of rearranged TCR-gamma genes, which represent a unique molecular marker for an individual lymphoid cell and a clonal disease developing from this cell. Using various strategies and gel electrophoretic systems, the PCR products can be separated to detect subsets of identical amplification products representing identical gene rearrangements in a clonal lymphoid population in the analyzed specimen. Although the molecular evidence for a monoclonal cell population as provided by PCR technology is an important factor in the diagnosis of a cutaneous lymphoma, only the synopsis of all available clinical, histomorphologic, immunohistochemical, and molecular data will lead to the adequate assessment of a cutaneous lesion.