OA-13: Increased levels of circulating tumor cells correlate with adverse clinical outcomes and distinct biological features in newly diagnosed patients with multiple myeloma

Introduction: Circulating tumor cells (CTCs) have shown an independent prognostic value in transplant-eligible (TE) patients (pts) with newly diagnosed multiple myeloma (NDMM). In this study, we aimed to evaluate the optimal clinical CTC cut-off for both TE and transplant ineligible (TI) NDMM pts, using the high-sensitive next generation flow-cytometry (NGF). Moreover, we performed matched analysis of both bone marrow (BM) and peripheral blood (PB) to highlight any possible inconsistencies between the two sites.

Methods: We studied 550 NDMM pts; 210 (38%) were TE and 340 (62%) were TI. NGF was used for the detection of clonal cells in both BM and PB. To define the optimal clinical cut-off of CTCs, we performed various multivariable regression models including CTCs, ISS (or R-ISS), cytogenetic status and LDH, and selected the one with the best performance. The median follow-up period was 41 months (range: 5-66 months). The BM niche profiling was examined with mass cytometry (CyTOF, n=15 pts) and various multicolor flow cytometry panels (n=199 pts) that allowed the detection of 32 distinct immune populations.

Results: CTCs were detected in 493/550 (89.6%) pts with a median value of 0.01% of all nucleated cells. Increased levels of CTCs correlated with advanced ISS stage (0.002%, 0.007% and 0.037% for pts with ISS-I, ISS-II and ISS-III respectively, p< 0.0001), high risk cytogenetics (median: 0.038% vs. 0.006% in standard risk, p< 0.0001), and higher levels of b2-microglobulin and BM infiltration. Pts with phenotypic inconsistencies between BM and PB had higher levels of CTCs and more often a diffuse MRI pattern than those with a phenotypic agreement (40% vs.10%, p< 0.01). The optimal clinical cut-off of CTCs was defined at 0.02%, stratifying pts in two different prognostic groups with high and low CTCs [median PFS: 40 months vs. not reached (NR), HR: 2.59, 95% CI:1.71-3.91, p< 0.0001]. In the multivariable analysis the 0.02% cut-off was independent from ISS and/or cytogenetics and was clinically relevant for both TI (median PFS: 47 vs. 23 months, p< 0.0001) and TE pts (median PFS: NR in both categories, p< 0.01). The 2-year probability of MRD negativity was 45% and 67% for pts with high and low CTCs; median time to MRD negativity was 34 vs. 17 months, respectively (HR:1.7, 95% CI:1.2-2.4, p=0.002). Of note, pts with high CTCs who achieved MRD negativity, modulated their unfavorable risk status and showed a similar PFS with those who had low CTCs. Beyond prognostication, pts with high CTC levels showed unique BM immune profiles characterized by increased levels of T cells, NK cells, TAMs and an increased memory/naive B cell ratio.

Conclusions: The presence of CTC at a level of >0.02% confers an adverse prognostic factor for NDMM pts, irrespective of their transplant status. Since the liquid biopsy is a better representative of the entire tumor load than a tissue biopsy sample, the analysis of CTCs may serve as the new hallmark for the real-time evaluation of a patient’s disease and immune status.