Abstract:
Background. Circulating tumor cells (CTC) are increasingly being recognized as a prognostic biomarker for risk stratification in newly diagnosed multiple myeloma (NDMM). High percentage of CTC have been associated with inferior minimal residual disease (MRD) negativity-rate and progression free survival (PFS) in 2 recent trials (Bertamini et al, JCO 2022; Garces et al, JCO 2022). However, the prognostic value of CTC in patients receiving quadruplet (anti CD38, proteasome inhibitors, immunomodulatory drugs, steroids), autologous transplant, and maintenance which represents a new standard of care in transplant eligible (TE) NDMM, has not been investigated.
Methods. Peripheral blood samples of NDMM enrolled in the multicenter phase III PERSEUS randomized trial (NCT03710603; Sonneveld et al, NEJM 2023) were centrally analyzed at Erasmus MC. CTC were phenotyped and enumerated by flow cytometry (EuroFlow) with a median sensitivity of 4e-06 (range 2e-06- 1.3e-04). MRD in bone marrow at 10-5 and 10-6 was measured by next-generation sequencing (clonoSEQ®). Overall MRD negativity (MRD-neg) rate was defined as the proportion of participants in the ITT population who achieved both MRD negativity and a CR or better. Sustained MRD-neg was defined as 2 consecutive MRD-negative results at least 12 months apart with no MRD-positive results in between. High risk cytogenetic abnormalities (HRCA) were defined as the presence of del17p, t(4;14) and/or t(14;16) by FISH.
Cox multivariate (MV) proportional hazards regressions were performed for PFS including CTC as continuous variable (log10) or categorical (Low vs High), ISS (I vs II / III), cytogenetics (HRCA no vs yes/unknown), LDH (lower vs higher of upper limit of normality), and therapy (without vs with daratumumab). The optimal CTC cutoff was established using Cox regressions for PFS adjusted for ISS, LDH, and HRCA, identifying the cutoff with the highest C-index (Bertamini et al, JCO 2022). Medians were compared with Kruskal Wallis test, frequencies with chi-square test.
Results. Out of 709 patients enrolled in the PERSEUS study, 451 were tested for CTC, based on sample availability. The median follow-up was 48 months. Before start of therapy, CTCs were detected in 396 patients (87%). Median CTC values were similar in both arms (D-VRd 0.010%, 95%CI 0.0009-0.074%; VRd 0.0088%, 95%CI 0.0012-0.075%; p=0.8). As a continuous variable, higher CTC were strongly correlated to worse PFS (HR 1.36, 95% CI 1.15-1.6, p=4.07e-04) independent of HRCA, LDH, ISS, and treatment arm. This translated in reduced 4-year PFS estimates with patients categorized by increasing log10 CTC levels (CTC <=0.001%: 93%, CTC 0.001-0.01%: 79%; CTC 0.01-0.1%: 71%; CTC 0.1-1%: 67%; CTC>1%: 48%; log-rank p<0.0001).
Previously reported CTC cut-offs (e.g. 0.01%, 0.07%) identified patients with reduced PFS in PERSEUS, testifying to the robustness of the biomarker. For further analyses an optimal cut-off of 0.175% was calculated for this dataset, identifying 15.3% of patients with CTC above the threshold (CTC-High, n=69/451). As already reported, MRD-neg rates were higher in patients treated with D-VRd vs VRd (Sonneveld, EHA 2024), and this was true also for CTC-High and CTC-Low (≤0.175%) patients. Overall MRD-neg rates in CTC-high patients were: 69% D-VRd vs 34% VRd (p=0.008, 10-5 threshold) and 47% D-VRd vs 22% VRd (p=0.054, 10-6 threshold).Sustained MRD-neg rates in CTC-High patients were: 50% D-VRd vs 16% VRd (p=0.004, 10-5 threshold) and 39% D-VRd vs 6% VRd (p=0.003, 10-6 threshold).
In terms of PFS, D-VRd was superior to VRd in both CTC-High (4-year PFS rates D-VRd 58% vs VRd 40%) and CTC-Low patients (4-year PFS rates D-VRd 88% vs VRd 74%, log-rank p<0.001). Finally, a small group of 34 ultra high-risk patients was identified by combining both CTC-High and HRCA (4 year-PFS: CTC-High HRCA 29% vs CTC-High Standard risk CA 73% vs CTC-Low HRCA 68% vs CTC-Low Standard risk CA 84%, log-rank p<0.001). However, analysis by treatment arm was not possible due to small numbers.
Conclusions. CTC is an independent prognostic factor in the context of the most effective standard of care for TE NDMM. The presence of both high CTC and HRCA identifies a group of patients with an overall dismal outcome. The addition of daratumumab to VRd induction/consolidation and R maintenance improves outcome in NDMM patients with high-risk disease defined by high CTC, leading to higher rates of deep and sustained MRD-neg and better PFS.
