Volume 2, Issue 2, July 2007
Dr. CHEUK Wah
BSc(Hons), MBBS, FHKCPath, FRCPA, Associate Consultant, Department of Pathology, Queen Elizabeth Hospital
Overview of conventional molecular techniques in lymphomas
The use of molecular techniques in hematolymphoid pathology started with cloning of the immunoglobulin and T cell receptor genes.  This is followed by the cloning of a number of translocation breakpoints in some common lymphoma types.[2-4] Assay of chromosomal breakpoints not only helps in confirming a clonal proliferation but also prov ides an indication of the type of lymphoma. The main application is to establish clonality or lineage of a lymphoid proliferation.
Southern blot analysis was the standard technique in molecular studies. The advent of the polymerase chain reaction (PCR) provides an alternative technical approach to Southern blot analysis, allowing molecular studies to be performed in many diagnostic laboratories. PCR technique is technically simpler, has a much faster turnaround time, requires a much smaller quantity of clinical materials, and can be performed on archival, formalin-fixed, paraffin-embedded samples (Figure 1). Advances in PCR techniques allow accurate quantitation of the template (real time PCR) and make it possible to use RNA as the starting material (revers transcriptase PCR). Fluorescence in situ hybridization (FISH) utilizes oligonucleotide probes to localize specific chromosomal segment so that translocation can be visualized under the fluorescence microscope. This “interphase cytogenetics” technique obvi ates the need of fresh specimen and cell culture and revolutionizes the traditional cytogenetics. Although FISH may not be as sensitive as PCR-based methods, it is superior in detecting complex karyotypic abnormalities involving multiple fusion partners and has lower false negative rates in detection of chromosomal translocations in some lymphoma types.