Interphase FISH: a rapid method for detecting malignant plasma cells in multiple myeloma patients submitted to autologous transplantation

Fluorescence in situ hybridization (FISH) on interphase nuclei has been sho wn to be an efficient method for detecting aneuploidy in multiple myeloma ( MM), The aim of this study was to test the feasibility of FISH techniques f or detecting malignant cells in the harvests of MM patients submitted to au tologous transplantation. As trisomy 9 (T9) is a frequent event in MM, we u sed it as a genetic marker of malignant plasma cells. T9 was detected in 45 out of 55 MM bone marrow samples (81.8%) using a chromosome 9 centromeric (C9C) probe. Twenty-four of the 55 MM patients were subjected to high-dose therapy followed by autologous unselected progenitor cell transplantation. Trisomy 9 was detected in 20 patients and was used as a marker of malignant cells. Upon karyotypic analysis, three of the four remaining patients with out To showed an unbalanced translocation leading to a complete trisomy of the long arm of chromosome 1 (T1q), We thus used a Iq juxtacentromeric prob e, pUC1.77, as another genetic marker of malignant plasma cells in these th ree further patients. FISH with C9C or pUC1.77 probes was performed on the harvests of these 23 patients and detected clonal cells in 11 transplants. The disease-free survival from graft was significantly longer for the patie nts who had no malignant cells in their transplant (P = 0.009), The median disease-free survival was 23 months in these patients, as compared to 12 mo nths in the patients whose transplant was contaminated. As almost all MM ar e cytogenetically abnormal, FISH with adequate probes represents a simple, quantitative tool for rapid detection of malignant cells in the harvests. O ur results also suggest that the presence of MM cells in the transplant may he predictive of poor outcome.