Molecular biology of cutaneous T-cell lymphomas

Actually, the diagnostic procedures for the molecular diagnosis and monitoring of a T-cell neoplasia on tissue sections or DNA extracted from cutaneous lesions include: a. the demonstration of clonality (a clone is a group of cells expanded from a single cell), of the lymphoid tissue infiltrates, by using molecular probes specific for the T-cell receptors (TCR); TCR-Gamma, TCR-Beta and, more rarely TCR-Delta subunits. This analysis, in the past done by using Southern-Blot method, may be performed by using polymerase chain reaction (PCR) non-radioactive very sensitive methods, such as heteroduplex analysis of TCR1 on DNA extracted from lesional skin and may be indicative of malignancy, because reactive cutaneous lymphoid infiltrates are usually polyclonal. b. the detection of chromosomal translocations by Southern-Blot, PCR on the extracted DNA or on tissue sections/cytological smears by the new fluorescence in situ hybridization (FISH) techniques : i.e. the t (2;5) translocation detected in the systemic CD30+ anaplastic large cell (ALC) lymphomas and not in primary cutaneous CD30+ LC lymphomas or lymphomatoid papulosis (LYP).2 c. the demonstration of oncogenes or oncosuppressor genes involvement, by PCR method or FISH, mainly useful to the understanding of the pathogenesis and the progress ion/trans­form ation processes characteristics of these diseases: such as p16, p53, lyt-10, tal-1.3 d. the involvement of specific viruses (by quantitative PCR or FISH), such as HTLV1 and EBV, but also HHV6, HHV7, HHV8. e. the demonstration of chromosomal imbalances on DNA extracted from the cutaneous lesion by using the array-CGH (comparative genomic hybridization): this is a technique for the comparative hybridization of the genome based on array; platforms in which genomic clones containing specific sequences of the human genome (genic and extragenic sequences) are located, the clones are distributed at different distances one from the other, depending from the type of array used. Traditional cytogenetic has a resolution of 10Mb, high resolution HR-CGH on metaphases has a resolution of 5 Mb, whereas array-GH has a resolution of 100Kb and now of 6Kb.4 f. the determination of the gene expression profile (GEP) of the infiltrate neoplastic cells on the tissue extracted RNA and cDNA, to look for marker genes (always low or highly expressed) to use for diagnosis, could be in imbalanced areas of the genome. Recently a group of 27 genes had been defined for the diagnosis of mycosis fungoides. In our study we analyzed by a very sensitive oligo-array. CGH methods the DNA extracted from the cutaneous lesions of a group of rare CTCL classified by the recent WHO/EORTC classification.5