Minimally Invasive Assessment of Measurable Residual Disease (MRD) in Multiple Myeloma (MM)

BACKGROUND

MRD is an established test in MM clinical trials but not in routine practice. A hindrance to its wider adoption is invasive bone marrow (BM) aspirates. Thus, the possibility of assessing MRD using minimally invasive methods could be paramount to facilitate its transition from clinical trials to routine practice, but also to improve patients’ (pts) quality of life and to generate more meaningful MRD results based on periodic assessments instead of limited time points. However, the methods developed for MRD evaluation in BM are less sensitive when used in peripheral blood (PB).

AIM

Investigate the complementarity and prognostic value of new multimodal minimally invasive MRD assessment in MM.

METHODS

This study included 243 transplant eligible and ineligible pts who were on maintenance or observation at the time of MRD assessment in PETHEMA/GEM clinical trials. In all cases, MRD was evaluated in PB using BloodFlow, which is a highly sensitive method (10^-7) that combines immunomagnetic enrichment with next-generation flow (NGF) cytometry. Periodic assessment of MRD in peripheral blood (PB) using BloodFlow was performed every six months. In 27 patients, MRD was further investigated in cfDNA using CloneSight, a highly sensitive (10^-4) next-generation sequencing method based on pt-specific mini-panels of multiplexed amplicons covering somatic mutations identified at diagnosis. In 169 of the 243 patients, MRD was analyzed in the serum using Quantitative Immunoprecipitation Mass Spectrometry (QIP-MS) with anti-IgG/A/M, total κ and λ beads.

RESULTS

BloodFlow was performed in a total of 867 PB samples, out of which 77 (9%) were MRD positive. The median number of CTCs/µL was 0.016 (range, 0.0003 - 0.29). In 506 of the 867 assessments, MRD was simultaneously analyzed in the BM using NGF. The concordance between BloodFlow in PB and NGF in BM was 78.9% (70.4% double negative and 8.5% double positive MRD results). The frequency of BloodFlow-/NGF+ and BloodFlow+/NGF- discordant assessments was 20.3% and 0.8%, respectively.

Serial assessment of MRD in PB using BloodFlow showed that 221 of the 243 (91%) pts had sustained MRD negativity and 13 (5%) were persistently positive. MRD conversions from negative to positive were noted in 9 (4%) pts. The landmark median PFS from the latest MRD assessment was not reached (NR) vs 3 months in negative vs positive patients (HR: 0.09, P < .001). Of note, only 11 of the 221 (5%) MRD negative pts relapsed thus far.

Of the 27 pts in whom MRD was simultaneously analyzed in cfDNA using CloneSight, five were MRD positive. The landmark median PFS from the latest MRD assessment was NR vs 5 months in negative vs positive pts (HR: 0.23, P = .057). The number of patients with BloodFlow-/CloneSight-, BloodFlow+/CloneSight-, BloodFlow-/CloneSight+ and BloodFlow+/CloneSight+ results were 17, 5, 2 and 3. The landmark median PFS from the latest MRD assessment in patients with double negative MRD vs positive by either method was NR vs 8 months (HR: 0.20, P = .056). Of note, only 2 of the 17 double negative MRD patients relapsed thus far.

Of the 169 pts in whom MRD was simultaneously analyzed in serum using QIP-MS, 37 (22%) were MRD positive. The landmark median PFS from the latest MRD assessment was NR in negative and positive patients (HR: 0.13, P < .001). The number of patients with BloodFlow-/QIPMS-, BloodFlow+/QIPMS-, BloodFlow-/QIPMS+ and BloodFlow+/QIPMS+ results were 130, 2, 26 and 11. The landmark median PFS from the latest MRD assessment in patients with double negative MRD vs positive by either method was NR and 8 months, respectively (HR: 0.07, P < .001). Of note, only 3 of the 130 (2%) double negative MRD patients relapsed thus far. The negative predictive value (NPV) of a double negative MRD detection in PB/serum using BloodFlow/QIP-MS and MRD negativity in BM using NGF was 86%.

CONCLUSIONS

This is the first study of multimodal minimally invasive MRD assessment in MM. Our results show that BloodFlow, CloneSight and QIP-MS are empowered to detect MRD with high sensitivity in PB, cfDNA and serum. The presence of CTCs, mutations and M-component was systematically associated with dismal PFS. The complementarity between these methods achieved a high NPV of MRD negativity in BM, and enabled the identification of multimodal MRD negative pts with very low risk of relapse. Thus, this study paves the way towards minimally invasive MRD assessment in MM pts on maintenance or observation.