THE DETECTION OF MINIMAL LYMPHOMA BY MOLECULAR AND COMBINED CULTURE-MOLECULAR METHODS

Seventy-four patients from a prospective randomized trial comparing au tologous bone marrow (ABM) versus blood stem cell (BSC) transplantatio n after high-dose chemotherapy for intermediate and high grade non-Hod gkin's lymphoma (NHL) were studied for the presence of residual lympho ma prior to transplantation. Pre-transplant bone marrow (BM), peripher al blood (PB) and the ABM or BSC harvest were studied by molecular ass ays immediately after collection and at weekly intervals after the ini tiation of in vitro cultures. B-NHLs with t(14;18) at the major breakp oint region (mbr) were monitored by detecting cells with the transloca tion. Other B-NHLs were monitored with tumour-specific primers and pro bes to the immunoglobulin heavy chain (IgH) gene complementary determi ning region (CDR) III. T-NHLs were similarly monitored using the T-cel l receptor gamma chain gene V-J junctional region as the tumour-specif ic marker, Of the 74 patients, seven did not have adequate tumour biop sies for molecular characterization. Of the remaining 67 cases, 35 had identifiable markers for follow-up studies and 20/35 cases (52%) had tumour cells detected in either the pretransplant BM/PB samples or the ABM/BSC harvest. Residual tumours were detected at a high frequency i n T-NHL (100%) and t(14;18)(+) B-NHL (86%) but at a lower frequency in B-NHLs without t(14,18) (44%). In five cases, one or more of the samp les were initially negative for residual lymphoma but became positive after a period of culture; additional studies confirmed that in vitro culture enhanced the sensitivity of tumour detection in about half of these samples. Molecular assay for minimal residual disease can be per formed in the setting of multicentre prospective clinical trials. The substantial frequency of failure of obtaining tumour-specific IgH CDRI II sequences in paraffin-embedded B-NHLs argues for the storage of fro zen tumour samples for possible molecular studies.