Clonal phylogeny and evolution of critical cytogenetic aberrations in multiple myeloma at single cell level by QM-FISH.

Single-cell analysis is of significant importance in delineate the exact phylogeny of subclonal population and in discovering subtle diversification. So far studies of intratumor heterogeneity and clonal evolution in multiple myeloma (MM) were largely focused at the bulk tumor population level. Here, we performed quantitative multi-gene fluorescence in situ hybridization (QM-FISH) in 129 longitudinal samples of 57 MM patients. All the patients had newly-diagnosed and relapsed paired samples. An expanded cohort of 188 MM patients underwent conventional FISH (cFISH) to validate the cytogenetic evolution in bulk tumor level. 43 of 57 patients (75.4%) harbored three or four cytogenetic clones at diagnosis. We delineated the phylogeny of subclonal tumor population and derived the evolutionary architecture in each patient. Patients with clonal stabilization had a significantly improved OS than those with other evolutionary patterns (median OS, 71.2 vs. 39.7 vs. 35.2 vs. 25.5 months, for stable, differential, branching and linear patterns, respectively, p=0.001). Besides, a high degree of consistency and complementarity across QM-FISH and cFISH was observed in evaluation of cytogenetic evolution pattern in MM. Survival after relapse were greater influenced by the presence of high-risk aberrations at relapse (hazard ratio =2.07) rather than present at diagnosis (hazard ratio=1.55). This study shows that QM-FISH is a valuable tool to elucidate the clonal architecture at single cell level. Clonal evolution pattern is of prognostic significance, highlighting the need for repeated cytogenetic evaluation in relapsed MM.