SOUTHERN BLOT ANALYSIS OF LYMPHOPROLIFERATIVE DISORDERS - USE AND LIMITATIONS IN ROUTINE SURGICAL PATHOLOGY

Antigen receptor gene rearrangement studies are a sensitive means of d etermining lineage and clonality in lymphoproliferative disorders (LPD s) which remain difficult to classify after assessment of morphology a nd immunohistochemistry (IHC). This study investigates the utility of genotyping LPDs in a surgical pathology laboratory servicing a large t eaching hospital. Ninety-eight specimens with detailed frozen (FS) and /or paraffin section IHC were studied, including 65 B-cell lymphomas, 14 T-cell lymphomas, 2 biopsies of T-zone dysplasia, one unclassifiabl e lymphoma, 8 Hodgkin's disease (HD) and 8 reactive nodes. Southern bl otting (SE) was performed on tumor and control DNA cleaved with restri ction enzymes EcoR1, Hind III and BamH1, using radiolabelled probes fo r the immunoglobulin heavy chain joining region, constant regions of k appa and lambda light chains, and the constant region of the T-cell re ceptor beta chain. All reactive nodes and those harbouring HD had DNA in the germline configuration, apart from J(H) rearrangement in one ca se each of HD and florid reactive hyperplasia. Of the non-Hodgkin's ly mphomas (NHL), 17% did not reveal clonal rearrangements (11% B-NHL; 44 % T-NHL). Most of the negative results could be explained by sampling error in partially involved nodes, highly polymorphous infiltrates whe re the neoplastic population may have been below the 1% threshold dete ctable by SE, and instances of anaplastic large cell lymphoma. After a ccounting for these cases, a 5% negative rate of genoclonality remaine d (3% B-NHL; 13% T-NHL). In the majority of NHL (95%), the diagnosis c ould be established on the basis of morphology and/or IHC alone. In on ly 4 cases was recourse to DNA analysis considered essential to distin guish between NHL and a reactive proliferation. In only 3 cases of NHL was genotyping needed to establish lineage (resolved in 2). In our la boratory SB is 5 times more expensive than FS-IHC (panel of 10 antibod ies); we therefore suggest that SE should be restricted to those few c ases where a diagnosis cannot be established by other means. It would be most cost-effective if such DNA studies were centralized in large l aboratories.