Lost and Gain of t(4;14) and t(11;14) in Multiple Myeloma Patients Between Relapse and diagnosis: An Illustration of Clonal Dynamic During Disease Course. an IFM Study

Abstract 196

Until recent data, MM concept implies that all clones are linearly related to each other and homogenous in their mutational landscape. However, studies are now contradicting this model and reveal a more complex clonal architecture of Darwinian-like somatic evolution, where tumor progression proceeds in a branching rather than in a linear manner, leading to substantial clonal diversity and coexistence of wide genetic heterogeneity. By use of serial genomic analysis at different points during the disease course of MM patients, Keats et al. found the existence of 3 temporal tumor types, which can either be genetically stable, linearly evolving, or heterogeneous clonal mixtures with shifting predominant clones. In order to confirm these data we study on a large cohort of MM patients the emergence or disappearence by FISH analysis of t(4;14) and t(11;14) between diagnosis and relapse. We selected 444 patients from the IFM cell collection for whom we had a FISH analysis at diagnosis and relapse. Among them, 342 were evaluable for proceeding to FISH analysis. Upon receipt, bone marrow plasma cells were sorted using nanobeads and an anti-CD138 antibody (RoboSep, Stem Cell Technologies). After immuno-magnetic sorting, the plasma cell suspension purity was verified, and only samples with at least 90% of plasma cells were kept. Cells were then fixed in Carnoy's fixative. To test plasma cells for the t(4;14) and t(11;14), we did use specific IGH-FGFR3 and IGH-CCND1 fusion probes (Abbott Molecular). Hybridizations were performed according to the manufacturer's instructions. For analysis, at least 100 plasma cells with correct signals were scored using a Zeiss epifluorescence microscope. Our population baseline data presents usual characteristics: median age at diagnosis was 57 years (36y to 82y), diagnosis was made between 18/05/2000 and 19/08/2008. Relapse occurred between 11/08/2000 and 04/02/2009, with a median PFS of 26.6 months. The t(4;14) was present at diagnosis in 16.7% of the patients (38/232), and 11% (36/322) at relapse; Chi2 test did not find statistical difference between incidence at diagnosis and relapse (p=0.12). The t(11;14) was present in 24.6% of patients at diagnosis (48/195) but only 10.7% (20/187) at relapse (p=0.002). The purpose of our study was to explore clonal evolution during myeloma course. The t(4;14) translocation appeared (negative at diagnosis and positive at relapse) in 13 patients (n=218; 5.96%). On the contrary, t(4;14) disappeared in 11 cases (5.04%, n=218). In the same way, t(11;14) appeared for only 2 patients (1.42%, n=141) and disappeared in six cases (4.25%, n=141). Interestingly, we did not see switch between emergence and disappearance of the two translocations; no patient changed his cytogenetic status for one translocation to the other one. This phenomenon represents an important percentage of patients: for t(4;14), 11% of patients changed their status and 5.67% for t(11;14). Our data are in link with a study by Keats et al. who identified an evolution of aCGH data on a cohort of 28 patients showing changes over time for all their patients. Even if our data did not identify one of the three temporal tumor types described by Keats, the diversity of our findings (gain or loss of t(11;14) or t(4;14) between diagnosis and relapse) is an illustration on a large cohort of the clonal diversity and evolution of MM.