Impact of Minimal Residual Disease Detection by Next-Generation Flow Cytometry in Multiple Myeloma Patients with Sustained Complete Remission after Frontline Therapy

Minimal residual disease (MRD) was monitored in 52 patients with sustained CR (≥2 years) after frontline therapy using next-generation flow (NGF) cytometry. 25% of patients initially MRD- reversed to MRD+. 56% of patients in sustained CR were MRD+; 45% at the level of 10⁻⁵; 17% at 10⁻⁶. All patients who relapsed during follow-up were MRD+ at the latest MRD assessment, including those with ultra-low tumor burden. MRD persistence was associated with specific phenotypic profiles: higher erythroblasts’ and tumor-associated monocytes/macrophages’ predominance in the bone marrow niche. NGF emerges as a suitable method for periodic, reproducible, highly-sensitive MRD-detection at the level of 10⁻⁶.

Quantitative phase imaging of cells in a flow cytometry arrangement utilizing Michelson interferometer-based off-axis digital holographic microscopy

We combined Michelson-interferometer-based off-axis digital holographic microscopy (DHM) with a common flow cytometry (FCM) arrangement. Utilizing object recognition procedures and holographic autofocusing during the numerical reconstruction of the acquired off-axis holograms, sharply focused quantitative phase images of suspended cells in flow were retrieved without labeling, from which biophysical cellular features of distinct cells, such as cell radius, refractive index and dry mass, can be subsequently retrieved in an automated manner. The performance of the proposed concept was first characterized by investigations on microspheres that were utilized as test standards. Then, we analyzed two types of pancreatic tumor cells with different morphology to further verify the applicability of the proposed method for quantitative live cell imaging. The retrieved biophysical datasets from cells in flow are found in good agreement with results from comparative investigations with previously developed DHM methods under static conditions, which demonstrates the effectiveness and reliability of our approach. Our results contribute to the establishment of DHM in imaging FCM and prospect to broaden the application spectrum of FCM by providing complementary quantitative imaging as well as additional biophysical cell parameters which are not accessible in current high-throughput FCM measurements.

Minimal Residual Disease Assessment Within the Bone Marrow of Multiple Myeloma: A Review of Caveats, Clinical Significance and Future Perspectives

There is an increasing clinical interest in the measure and achievement of minimal residual disease (MRD) negativity in the bone marrow of Multiple Myeloma (MM) patients, as defined equally either by Multicolor Flow Cytometry (MFC) or by Next Generation Sequencing (NGS) technologies. At present, modern technologies allow to detect up to one on 104 or on 105 or even on 106 cells, depending on their throughput. MFC approaches, which have been progressively improved up to the so-called Next Generation Flow (NGF), and NGS, which proved clear advantages over ASO-PCR, can detect very low levels of residual disease in the BM. These methods are actually almost superimposable, in terms of MRD detection power, supporting the lack of unanimous preference for either technique on basis of local availability. However, some technical issues are still open: the optimal assay to use to detect either phenotype (e.g., next generation multidimensional flow cytometry, imaging) or genotype aberrations (e.g., ASO-RQ PCR, digital droplet PCR, NGS) and their standardization, the sample source (BM or peripheral blood, PB) and its pre-processing (red-cell lysis vs. Ficoll, fresh vs. frozen samples, requirement of CD138+ cells enrichment). Overall, MRD negativity is considered as the most powerful predictor of favorable long-term outcomes in MM and is likely to represent the major driver of treatment strategies in the near future. In this manuscript, we reviewed the main pitfalls and caveats of MRD detection within bone marrow in MM patients after front-line therapy, highlighting the improving of the currently employed technology and describing alternative methods for MRD testing in MM, such as liquid biopsy.

Challenges and opportunities in the assessment of measurable residual disease in multiple myeloma

Treatment response assessment in multiple myeloma (MM) relies on the detection of paraprotein in serum and/or urine, bone marrow morphology and immunohistochemistry. With remarkable advances in therapy, particularly in the newly diagnosed setting, achievement of complete remission became frequent, creating the need to identify smaller amounts of residual disease and understand their prognostic and therapeutic implications. Measurable residual disease (MRD) can be assessed primarily by flow cytometry and next generation sequencing and state-of-the-art assays have sensitivity approaching 1 in 10⁶ cells. This review discusses the existing challenges in utilizing MRD to inform management of MM and highlights open research questions and opportunities as MRD is more routinely incorporated into clinical practice for patients with MM.

Minimal Residual Disease in Multiple Myeloma: Impact on Response Assessment, Prognosis and Tumor Heterogeneity

Multiple Myeloma (MM) therapy has evolved rapidly over the past decade. With current multidrug combinations and autologous transplant, rates of overall response exceed 90% and complete response (CR) more than 50% in some studies. Unfortunately, despite higher rates of CR, relapse rates remain high suggesting that persistent disease may not be measured by current techniques. Traditionally, response rates were defined by urine and serum protein electrophoresis, immunofixation and histopathological absence of clonal plasma cells in the bone marrow. Currently, there are several validated sensitive assays to evaluate for MRD (minimal residual disease); multiparameter flow cytometry (MFC) including nextgeneration flow cytometry (NGF), next-generation sequencing (NGS), and allele specific oligonucleotide quantitative polymerase chain reaction (ASO-qPCR). These methods have provided a means to quantitatively assess residual disease and accurately prognosticate PFS and OS in myeloma. In this chapter, we will discuss the current techniques for MRD detection as well as describe techniques that are emerging for improved characterization of drug resistant residual populations that could be adapted for MRD monitoring in the future. While improved therapies are able to eradicate the dominant clone, resistant sub-clones persist and remain undetectable even by MRD techniques. Characterization of these clones will help design therapies against drug-resistant clones and move us closer to a cure in MM.

Efficacy and safety of autologous stem cell transplantation after induction therapy with lenalidomide, bortezomib, and dexamethasone

OBJECTIVES

Recently, phase III trials assessed a new combination of lenalidomide, bortezomib, and dexamethasone (RVD) in induction therapy in transplantation-eligible multiple myeloma (MM) patients, before consolidation with RVD and lenalidomide maintenance. We present a retrospective study evaluating this approach with patients from the real life.

METHODS

We conducted a retrospective single-arm study to assess efficacy and safety of RVD combination in induction therapy before high-dose chemotherapy with melphalan followed by autologous stem cell transplantation, and RVD consolidation followed by lenalidomide maintenance, from February 2011 to May 2016.

RESULTS

Forty patients were enrolled. The mean age at diagnosis was 56 years. Median progression-free survival was 45 months, and median overall survival was 76 months. The only factor found associated with better PFS was a negative minimal residual disease (P < .01). Twenty-six (65%) patients experimented adverse events: 8 patients (20%) underwent 12 serious AE (≥grade 3). Treatment discontinuation occurred in 2 patients (5%) because of severe AE.

CONCLUSION

To our knowledge, this work provides the first evidence of the efficacy and the safety of RVD combination in patients treated in common practice.

Monitoring of Measurable Residual Disease in Multiple Myeloma by Multiparametric Flow Cytometry

Recent interest in high sensitivity multiple myeloma (MM) measurable residual disease (MRD) testing is a direct consequence of the high-quality responses achieved using novel therapeutic agents and better treatment strategies. Traditional diagnostic measures such as immunohistochemistry and morphology have detection sensitivities of only 10^-2 - 10^-3, which do not reliably predict progression free survival (PFS) or overall survival (OS) after these treatments. Contemporary monitoring of MM MRD has switched to more sensitive platforms such as quantitative allele-specific oligonucleotide polymerase chain reaction (ASO-qPCR), next-generation sequencing (NGS), and multiparametric flow cytometry (MFC). Though both ASO-qPCR and NGS have excellent detection sensitivities (10^-5 - 10^-6), both technologies have lower applicability when compared to MFC. Conventional MFC can easily reach a detection sensitivity of 10^-4 and when optimized can achieve a sensitivity of 10^-5 - 10^-6. Current consensus guidelines require a minimum of 2 million and recommend 5 million events be acquired to reach a minimum sensitivity of 10^-5. As conventional immunophenotyping protocols are unable to attain these numbers, alternative MFC staining procedures are required. This manuscript describes two high-sensitivity MFC approaches that can be used for MM MRD testing.

Bortezomib, thalidomide, and dexamethasone with or without daratumumab before and after autologous stem-cell transplantation for newly diagnosed multiple myeloma (CASSIOPEIA): a randomised, open-label, phase 3 study

BACKGROUND

Bortezomib, thalidomide, and dexamethasone (VTd) plus autologous stem-cell transplantation is standard treatment in Europe for transplant-eligible patients with newly diagnosed multiple myeloma. We evaluated whether the addition of daratumumab to VTd before and after autologous stem-cell transplantation would improve stringent complete response rate in patients with newly diagnosed multiple myeloma.

METHODS

In this two-part, randomised, open-label, phase 3 CASSIOPEIA trial, we recruited transplant-eligible patients with newly diagnosed multiple myeloma at 111 European sites. Patients were randomly assigned (1:1) to receive four pre-transplant induction and two post-transplant consolidation cycles of VTd alone (VTd group) or in combination with daratumumab (D-VTd group). The primary endpoint of part 1 was stringent complete response assessed 100 days after transplantation. Part 2 (maintenance) is ongoing. The trial is registered with ClinicalTrials.gov, number NCT02541383.

FINDINGS

Between Sept 22, 2015, and Aug 1, 2017, 1085 patients were enrolled at 111 European sites and were randomly assigned to the D-VTd group (n=543) or the VTd group (n=542). At day 100 after transplantation, 157 (29%) of 543 patients in the D-VTd group and 110 (20%) of 542 patients in the VTd group in the intention-to-treat population had achieved a stringent complete response (odds ratio 1·60, 95% CI 1·21-2·12, p=0·0010). 211 (39%) patients in the D-VTd group versus 141 (26%) in the VTd group achieved a complete response or better, and 346 (64%) of 543 versus 236 (44%) of 542 achieved minimal residual disease-negativity (10^-5 sensitivity threshold, assessed by multiparametric flow cytometry; both p<0·0001). Median progression-free survival from first randomisation was not reached in either group (hazard ratio 0·47, 95% CI 0·33-0·67, p<0·0001). 46 deaths on study were observed (14 vs 32, 0·43, 95% CI 0·23-0·80). The most common grade 3 or 4 adverse events were neutropenia (28% vs 15%), lymphopenia (17% vs 10%), and stomatitis (13% vs 16%).

INTERPRETATION

D-VTd before and after autologous stem-cell transplantation improved depth of response and progression-free survival with acceptable safety. CASSIOPEIA is the first study showing the clinical benefit of daratumumab plus standard of care in transplant-eligible patients with newly diagnosed multiple myeloma.

FUNDING

The Intergroupe Francophone du Myélome and Dutch-Belgian Cooperative Trial Group for Hematology Oncology.

Prognostic value of minimal residual disease and polyclonal plasma cells in myeloma patients achieving a complete response to therapy

Achievement of a complete response has been associated with improved outcomes in patients with multiple myeloma. Recently, increasing application of minimal residual disease (MRD) assessment has shown that MRD negativity is a powerful prognostic factor for survival outcomes. We wanted to examine the impact of the polyclonal plasma cell (pPC) compartment among patients in complete response (CR) but are MRD positive. This is a retrospective cohort study where 460 myeloma patients were identified who met criteria for CR and had multicolor flow cytometry performed on the bone marrow (BM). Monoclonal and pPCs were estimated during MRD testing. Final outcomes including overall survival (OS) and time to next treatment (TTNT) were compared among the groups. The median OS for the entire cohort was not reached (95% CI; 63 mos, NR) and the median TTNT was 31 months (95% CI; 27,36). Among the MRD_neg group, median TTNT was 37.6 months vs 23 months for MRD_pos patients (P < .001); the median OS was not reached for either group, but there was a trend toward better survival for MRD_neg patients. Among the MRD_pos group, median percentage of pPCs was 65% (2.5-98.5), and those with >95% pPCs had a significantly better TTNT (NR vs 23 months; P = .02) and a trend toward better OS. We conclude that achievement of MRD negativity predicts for better response durability and trend toward improved OS and an increased proportion of pPC predicts for better outcomes within those who have residual tumor cells highlighting the importance of marrow normalization.

High-dose bendamustine and melphalan conditioning for autologous stem cell transplantation for patients with multiple myeloma

High-dose melphalan (MEL200) followed by autologous stem cell transplantation (ASCT) remains a standard of care for multiple myeloma (MM). Bendamustine induces responses in MM resistant to other alkylators. Our prior Phase I trial adding bendamustine to MEL200 transplant conditioning resulted in no additional toxicity. We now report a single-arm, phase II study that evaluated the efficacy of bendamustine 225 mg/m² with MEL200 conditioning for ASCT in 18 patients with newly diagnosed MM (NDMM) and 17 with relapsed or refractory MM (RRMM). The primary end point was the complete response (CR/sCR) rate at day+ 100. Sample size was determined according to Simon's two-stage design. At stage 1, sixteen patients entered the study. As there were eight patients with CR/sCR, enrollment increased to 28 patients. Sixteen out of the first 28 evaluable patients achieved CR/sCR, meeting the design criteria. Enrollment was then expanded to a total of 35 patients. 51% achieved a CR/sCR. After a median follow-up of 65 months, 21 patients progressed, including 7 deaths. The median PFS for NDMM and RRMM was 48 and 45 months, respectively. Bendamustine/MEL200 conditioning resulted in excellent overall and depth of response as well as PFS, particularly in the RRMM patients, and is worthy of further investigation (NCT00916058).

The impact of re-induction prior to salvage autologous stem cell transplantation in multiple myeloma

Autologous stem cell transplantation (ASCT) is an integral component of the therapeutic arsenal in multiple myeloma. Given that overall survival (OS) is comparable between patients receiving up-front or delayed ASCT, some opt to collect stem cells and postpone transplant until the time of disease progression (i.e. salvage ASCT). It is unknown if induction should be repeated prior to salvage ASCT, or if patients should proceed directly. We identified 234 patients who underwent salvage ASCT at our institution: 188 (80%) were re-induced, whereas 46 (20%) proceeded directly without re-induction. There was no significant difference in time to next therapy (TNT) or OS from Day 0 between the two groups. Patients who were re-induced had a nonsignificant trend towards a higher rate of complete response post-ASCT (45% vs. 33%, p= .12). In multivariate models, re-induction did not affect TNT/OS. In the subgroup of 188 patients who were re-induced, patients with relapsed/refractory disease at the time of ASCT had significantly shorter TNT/OS compared to patients with deeper pre-ASCT responses. In summary, there was no survival difference for patients who were re-induced before salvage ASCT. However, many factors affect the decision to re-induce, and prospective studies would be required to discern its role definitively.

Immune Signatures Associated With Clonal Isotype Switch After Autologous Stem Cell Transplantation for Multiple Myeloma

BACKGROUND

High-dose chemotherapy and autologous stem cell transplantation (ASCT) are integral components of the overall treatment for patients with multiple myeloma (MM) aged ≤ 65 years. The emergence of oligoclonal immunoglobulin bands (ie, immunoglobulins differing from those originally identified at diagnosis [termed clonal isotype switch (CIS)]) has been reported in patients with MM after high-dose chemotherapy followed by autologous stem cell transplantation. However, the clinical relevance and the correlation with immune reconstitution remains unclear.

PATIENTS AND METHODS

Patients with MM who had undergone ASCT from 2007 to 2016 were included in the present study. The percentage of natural killer cells, B-cells, and T-cells was measured using flow cytometry in pre- and post-ASCT bone marrow samples. CIS was defined as the appearance of a new serum monoclonal spike on serum protein electrophoresis and immunofixation that differed from original heavy or light chain detected at diagnosis.

RESULTS

A retrospective analysis of 177 patients with MM who had undergone ASCT detected CIS in 39 (22%). CIS after ASCT correlated with improved progression-free survival (52.2 vs. 36.6 months; P = .21) and overall survival (75.1 vs. 65.4 months; P = .021). Patients with a relapse had an isotype that differed from a CIS, confirming the benign nature of this phenomenon. CIS was also associated with lower CD8 T-cell percentages and a greater CD4/CD8 ratio (2.8 vs. 0.2; P = .001) compared with patients who did not demonstrate a CIS, suggestive of more profound T-cell immune reconstitution in this group.

CONCLUSION

Taken together, our data have demonstrated that a CIS is a benign phenomenon and correlates with a reduced disease burden and enriched immune repertoire beyond the B-cell compartment.

Antioxidant Defenses Confer Resistance to High Dose Melphalan in Multiple Myeloma Cells

Background: Multiple myeloma (MM) is the second most common hematological cancer after lymphoma. It is characterized by the accumulation of clonal malignant plasma cells within the bone marrow. The development of drug resistance remains a major problem for effective treatment of MM. Understand the mechanisms underlying drug resistance in MM is a focal point to improve MM treatment. Methods: In the current study, we analyzed further the role of redox imbalance induction in melphalan-induced toxicity both in human myeloma cell lines (HMCLs) and primary myeloma cells from patients. Results: We developed an in-vitro model of short-term resistance to high-dose melphalan and identified that pretreatment with physiological concentration of GSH protects HMCLs from melphalan-induced cell cycle arrest and cytotoxicity. We validated these results using primary MM cells from patients co-cultured with their bone marrow microenvironment. GSH did not affect the ability of melphalan to induce DNA damages in MM cells. Interestingly, melphalan induced reactive oxygen species, a significant decrease in GSH concentration, protein and lipd oxydation together with NRF2 (NF-E2-related factor 2) pathway activation. Conclusions: Our data demonstrate that antioxidant defenses confers resistance to high dose melphalan in MM cells, supporting that redox status in MM cells could be determinant for patients’ response to melphalan.

Standardized assay for assessment of minimal residual disease in blood, bone marrow and apheresis from patients with plasma cell myeloma

The recent advances in myeloma treatment result in significantly better outcomes, defined as increased progression free survival (PFS) and overall survival (OS). Since there is a proven correlation between the extend of response and prolonged survival, there is an urgent need for highly sensitive assays for the detection of minimal residual disease (MRD). Next generation flow cytometry has become a valuable approach for sensitive evaluation of the depth of complete response (CR). Here, we report the diagnostic performance and validation results of a single-tube 9-color panel assay. The validation design included intra-assay analysis measuring accuracy, inter-assay analysis estimating method’s linearity and precision and inter-assay analysis evaluating repeatability. Furthermore, in inter-operator analysis assessed the comparability of the result analysis of different operators. Staining stability was evaluated in age-of-stain experiments. Our validation results show that a reliable detection of residual myeloma cells is feasible to a detection level of 10⁻⁵ with a single-tube assay for a variety of materials (peripheral blood, bone marrow and stem cell apheresis). This study establishes highly sensitive, fully standardized approach for MRD detection in myeloma that is ready for implementation in routine diagnostic laboratories.

[Role of minimal residual disease detection by multiparameter flow cytometry in newly diagnosed multiple myeloma: an analysis of 106 patients]

目的

探讨多参数流式细胞术（MFC）检测微小残留病（MRD）在我国初诊多发性骨髓瘤（MM）患者中的可行性及其预后意义。

方法

回顾性分析2013年6月至2015年6月106例采用MFC进行MRD检测连续收治的初诊MM患者的临床资料。

结果

①106例患者中48例（45.3%）MRD转为阴性，中位达MRD阴性时间为3个月。接受自体造血干细胞移植（ASCT）患者MRD转阴率显著高于未接受ASCT患者（62.2%对36.2%，χ²=6.536，P=0.011）。②48例完全缓解（CR）患者中7例（14.6%）MRD持续阳性，这7例患者中5例已疾病进展，中位无进展生存（PFS）时间为19个月，3例死亡，中位总生存（OS）时间为28个月，MRD持续阳性CR患者的PFS及OS时间均明显短于MRD转阴CR患者（P值均<0.05）。③中位随访38个月，MRD转阴患者的预后显著优于阳性患者，二者中位PFS时间分别为未达到和17个月（P<0.001），中位OS均未达到（P<0.001）。根据MRD水平将患者分为四组：≥1%、0.1%~<1%、0.01%~<0.1%和阴性，结果显示随着MRD水平的降低，患者PFS及OS时间有逐渐延长趋势。④多因素分析显示，MRD是影响MM患者PFS[HR=0.133（95% CI 0.062~0.288），P<0.001]和OS[HR=0.156（95% CI 0.050~0.484），P=0.001]的独立预后因素。根据MRD、细胞遗传学情况将患者分为4组，结果显示MRD转阴的高危患者预后（PFS及OS）明显好于MRD阳性的高危患者（P<0.05），而与MRD转阴的标危患者预后相近（P>0.05）。

结论

ASCT患者中MFC检测的MRD转阴率更高。MRD是MM患者的独立预后因素，根据MRD水平可以对患者预后进行分层。MRD转阴的细胞遗传学高危患者的预后与标危患者相近。MFC检测MRD值得在临床推广应用。

Achieving minimal residual disease-negative by multiparameter flow cytometry may ameliorate a poor prognosis in MM patients with high-risk cytogenetics: a retrospective single-center analysis

The aim of our study was to evaluate the prognostic impact of minimal residual disease (MRD) and high-risk cytogenetics (HRCs) on outcomes in multiple myeloma (MM) patients. We applied multiparameter flow cytometry (MFC) to detect MRD in 123 consecutive patients diagnosed with MM for the first time who achieved very good partial remission (VGPR) or better after bortezomib or thalidomide-based induction therapy. Moreover, we examined the cytogenetic features of MM patients using magnetic-activated cell sorting and interphase fluorescence in situ hybridization (MACS-iFISH) at diagnosis. In all 123 MM patients, progression-free survival (PFS) and overall survival (OS) were better in the MRD- group (n = 31) than in the MRD+ group (n = 92) (median PFS: not reached (NR) vs. 26 months (m), P = 0.0002; 4-year OS, 91.7% vs. 66.3%, P = 0.008). PFS and OS were significantly shorter for each increase of one log per MRD level (P < 0.0001 and P = 0.001). The median PFS of the four groups according to the ratio of aberrant plasma cells (less than 0.01%, 0.01-0.1%, 0.1-1%, and more than 1%) were NR, 37 m, 26 m, and 15 m, respectively, and the 4-year OS rates were 91.7%, 69.3%, 76.1%, and 54.0%, respectively. In addition, our results show that PFS and OS were better for the standard-risk cytogenetic (SRC) patients than the HRC patients (median PFS: NR vs. 26 m, P = 0.004; 3-year OS: 95.8% vs. 76.0%, P = 0.006). The independent predictors of PFS were HRC and MRD+, which had hazard ratios of 1.901 (95% CI 1.094-3.303) and 3.486 (95% CI 1.449-8.386), respectively; while those for OS were an LDH level ≥ 250 U/L, HRC, and MRD+, which had hazard ratios of 2.789 (95% CI 1.080-7.199), 2.697 (95% CI 1.053-6.907), and 7.714 (95% CI 1.040-57.227), respectively. Furthermore, for SRC patients or HRC patients, PFS and OS were all longer in MRD- than in MRD+ patients. Strikingly, there was no significant difference in PFS or OS between the MRD-HRC and MRD+SRC groups (median PFS 45 vs. 34 m, P = 0.300; 4-year OS 100% vs. 83.6%, P = 0.196). PFS was superior in MRD-SRC than in MRD-HRC (NR vs. 45 m, P = 0.035); however, there was no significant difference in the 4-year OS between MRD-SRC and MRD-HRC (87.5% vs 100%, P = 0.480). MRD+ and HRCs were both independent prognostic factors in MM patients. Moreover, achieving MRD- may ameliorate a poor prognosis in MM patients with HRCs.

High-risk myeloma and minimal residual disease postautologous-HSCT predict worse outcomes

The aim of our study was to determine the impact of high-risk disease (HRD) and MRD on outcomes in myeloma patients receiving bortezomib-based induction followed by autologous hematopoietic stem cell transplant (auto-HSCT). HRD included t(4:14), t(14;16), del 17p, del 1p and/or amplification 1q by cytogenetics/FISH; all others were standard-risk disease (SRD). A subset of 165 newly diagnosed myeloma patients in a 2:1 ratio of HRD:SRD was generated using propensity score based nearest neighbor matching. Multiparametric flow cytometry (MFC) was used to detect MRD after auto-HSCT in select patients. MRD+ status at 3 months post auto-HSCT (hazard ratio (HR = 4.23, p = .028) and HRD (HR = 1.72, p = .026) were associated with a shorter PFS. Similarly, MRD+ 3 months post auto-HSCT (HR = 6.93, p = .08) and HRD (HR = 3.54, p < .001) and were associated with a shorter OS. Despite bortezomib-based induction, upfront auto-HSCT, and use of maintenance therapy, PFS and OS remained worse in MRD+ and HRD patients.

Flow Cytometric MRD Detection in Selected Mature B-Cell Malignancies

The quantification of submicroscopic minimal residual disease (MRD) after therapy proved to have independent prognostic significance in many mature B-cell malignancies. With the advent of routine benchtop cytometers capable of simultaneously analyzing ≥4 colors and with improved standardization, flow cytometry has become the method of choice for MRD assessments in some lymphoma entities. Herein we describe general aspects of flow cytometric standardization. Chronic lymphocytic leukemia and multiple myeloma (MM) are used as examples to explain the technical standardization of flow cytometry for MRD detection according to EuroFlow strategies. MRD data acquisition and detailed analysis using a newly developed approach (so-called next generation flow, NGF) in MM is a particular focus of this chapter.

Toward personalized treatment in multiple myeloma based on molecular characteristics

To date, the choice of therapy for an individual multiple myeloma patient has been based on clinical factors such as age and comorbidities. The widespread evolution, validation, and clinical utilization of molecular technologies, such as fluorescence in situ hybridization and next-generation sequencing has enabled the identification of a number of prognostic and predictive biomarkers for progression-free survival, overall survival, and treatment response. In this review, we argue that in order to continue to improve myeloma patient outcomes incorporating such biomarkers into the routine diagnostic workup of patients will allow for the use of personalized, biologically based treatments.

Minimal residual disease and log-reduction of plasma cells are associated with superior response after double autologous stem cell transplant in younger patients with multiple myeloma

BACKGROUND

Optimization of chemotherapy regimens in the treatment of multiple myeloma (MM) has led to increase the frequency of cases with complete response (CR). Nonetheless, many MM patients still experience relapse, suggesting that CR represents a suboptimal response criteria, and that new therapeutic strategies are needed after single transplant. However, the role of double autologous stem cell transplant (ASCT) as new adjunctive strategy remains to be elucidated. Indeed, we investigated the role of minimal residual disease (MRD) and log-reduction of plasma cells (PCs) as predictors of outcome and in quantifying the degree of tumor reduction after any ASCT.

METHODS

MRD and log-reduction were assessed by a six-color flow cytometry (FC) at different time-points: post induction, post first-, and post-second ASCT.

RESULTS

A significant difference was evidenced among the three time points for both log-reduction (P < 0.001) and MRD (P = 0.005). MRD levels after double ASCT were lower than MRD levels achieved after single ASCT (P = 0.005) and after induction (P < 0.001). Frequency of MRD positive patients after double ASCT was significantly lower rather than after the first ASCT (P = 0.008) and after induction (P = 0.004). Interestingly, a significant reduction of PFS was observed in patients with an unfavorable-risk cytogenetic (P < 0.001) and patients with MRD over 0.01% (P = 0.001) as well as log-reduction lower than 2.57 (P = 0.018) after double ASCT.

CONCLUSIONS

Our results show that a better clearance of myeloma cells is observed after the double ASCT, and a longer PFS is associated with a lower MRD. © 2018 International Clinical Cytometry Society.

Minimal residual disease negativity using deep sequencing is a major prognostic factor in multiple myeloma

The introduction of novel agents has led to major improvements in clinical outcomes for patients with multiple myeloma. To shorten evaluation times for new treatments, health agencies are currently examining minimal residual disease (MRD) as a surrogate end point in clinical trials. We assessed the prognostic value of MRD, measured during maintenance therapy by next-generation sequencing (NGS). MRD negativity was defined as the absence of tumor plasma cell within 1 000 000 bone marrow cells (<10-6). Data were analyzed from a recent clinical trial that evaluated the role of transplantation in newly diagnosed myeloma patients treated with lenalidomide, bortezomib, and dexamethasone (RVD). MRD negativity was achieved at least once during maintenance in 127 patients (25%). At the start of maintenance therapy, MRD was a strong prognostic factor for both progression-free survival (adjusted hazard ratio, 0.22; 95% confidence interval, 0.15-0.34; P < .001) and overall survival (adjusted hazard ratio, 0.24; 95% confidence interval, 0.11-0.54; P = .001). Patients who were MRD negative had a higher probability of prolonged progression-free survival than patients with detectable residual disease, regardless of treatment group (RVD vs transplant), cytogenetic risk profile, or International Staging System disease stage at diagnosis. These results were similar after completion of maintenance therapy. Our findings confirm the value of MRD status, as determined by NGS, as a prognostic biomarker in multiple myeloma, and suggest that this approach could be used to adapt treatment strategies in future clinical trials.

BrdU incorporation in multiparameter flow cytometry: A new cell cycle assessment approach in multiple myeloma

BACKGROUND

Mutiple myeloma (MM) is a neoplasia characterized by the accumulation of malignant plasma cells (PC) in the bone marrow. Although proliferation markers have been studied in MM, none of the current staging systems include them. Moreover, approaches used to analyze proliferation do not separate MM cells (MMCs) from normal PC.

METHODS

In this study, we combined multiparameter flow cytometry and BrdU incorporation or Ki67 staining to analyze MM cell proliferation in 44 monoclonal gammopathy of undetermined significance (MGUS), 153 newly diagnosed MM patients and 69 MM patients at relapse. The prognostic value of proliferation assessment was analyzed in 60 newly diagnosed patients treated with high-dose chemotherapy supported by autologous hematopoietic stem cell transplantation.

RESULTS

The median number of proliferating malignant PC significantly increases during MM disease progression. MM patients with a percentage of proliferating MMCs greater than 1.42% using BrdU/DAPI or greater than 1.1% using ki67/DAPI, are associated with a significantly shorter event free survival compared with patients with a lower percentage of proliferating MMCs.

CONCLUSIONS

Combination of flow cytometry with BrdU or ki67/DAPI staining could become a standard for the determination of MM cell proliferation. Furthermore, in the context of new effective myeloma treatment options, assessment of MM cell proliferation may be valuable, in clinical trials, to identify novel agents that could significantly affect the small proliferative compartment of MM cells. © 2018 International Clinical Cytometry Society.

[Comparison and analysis of minimal residual disease in multiple myeloma patients detected by 4-color and 8-color fluorescence antibody panels]

目的

探讨与比较4色和8色荧光抗体组合检测多发性骨髓瘤（MM）患者治疗后微小残留病（MRD）的灵敏度。

方法

建立一组以CD38/CD138对浆细胞进行设门，同时检测胞膜抗原CD45、CD19、CD56、CD117及胞质轻链cKappa、cLambda的8色抗体组合；6组4色抗体组合中，4组以CD38/CD138设门，分别分析CD45/CD19、CD56/CD117、CD19/CD56胞膜抗原（M1-3）和胞质轻链（C组）表达；MC1-2组分别以CD38/SSC和CD138/SSC设门，同时检测CD19或CD45胞膜抗原和胞质轻链。采用以上组合对20名健康志愿者和73例完全缓解后MM患者标本进行检测并进行比较分析。

结果

8色组合识别异常浆细胞（aPCs）和克隆性浆细胞（cPCs）的阳性率均为82.19%，一致率为89.04%（65/73）；cPCs中位比例为0.105%，均显示明显的单克隆轻链；敏感度为0.004%。CD38/SSC设门的浆细胞比例明显高于CD38/CD138（P<0.001）和CD138/SSC（P=0.001）设门。4色组合中C-_胞质组MRD阳性率最低，仅为65.75%，明显低于8色组合的82.19%（P=0.024）；M2-_56/117组检测的aPCs比例最低，为0.095%，与其他组相比差异有统计学意义（P=0.014）；MC1-_CD38和MC2-_CD138组，以cPCs作为判断标准时MRD阳性率均高于以aPCs为判断标准（P<0.05），结果一致率分别为68.49%（50/73）和79.45%（58/73）。与8色组合相比，4色组合中MC2-_CD138组敏感性、准确性和阴性预测值最高，阳性预测值和特异性也较高；其次是M1-_45/19组。

结论

CD38/CD138设门更准确，反映克隆性的胞质轻链检测较胞膜抗原更敏感，胞膜抗原异常表达并不完全代表为cPCs，建议胞膜抗原和胞质轻链同时检测。有条件者建议选用8色组合，4色组合中建议同时采用M1-_45/19和MC2-_CD138组合。

Novel biomarkers in multiple myeloma

Significant advancements have been made in the molecular mechanisms of myelomagenesis, diagnostic methods, prognostication, and the treatment options in multiple myeloma (MM) over the last decade. Despite these, MM remains a heterogeneous disease with differing outcomes. As myeloma treatment landscape continues to expand, personalized treatment that provides maximum benefit to a specific patient becomes more important. In the last few years, serum monoclonal proteins including the serum-free light chain assays, imaging, and cytogenetics have been used to predict the outcomes of MM patients receiving different types of therapies. With the development of novel technologies, more sensitive detection of residual disease using flow cytometry and next-generation sequencing has been possible. In addition, liquid biopsies using circulating tumor cells, tumor DNA, and novel immune biomarkers are potentially being investigated. These novel potential biomarkers not only accurately detect the mutational landscape of different cancers compared to standard methods but also serve as prognostic and predictive biomarkers for disease relapse and response to therapy. It is likely that we will be able to offer more targeted and risk-adapted therapeutic approach to patients with MM at different stages of their disease guided by these potential biomarkers.

The role of surface molecule CD229 in Multiple Myeloma

The outcome of Multiple Myeloma (MM) patients has dramatically improved, however, most patients will still succumb to their disease. Additional therapeutic options are urgently needed and novel immunotherapies are enormously promising in the therapeutic armamentarium against MM. The first step in the development of any immunotherapy needs to be the identification of an appropriate target structure. In this review we present the current knowledge on surface molecule CD229, a member of the Signaling Lymphocyte Activation (SLAM) family of immune receptors. We believe that based on its characteristics, including (1) strong and homogenous expression on all myeloma cells, (2) expression on myeloma precursors, (3) absence from most normal tissues, (4) a central function in the biology of MM, CD229 (SLAMF3) represents a promising target for anti-MM immunotherapies. The introduction of novel anti-CD229 approaches into the clinic will hopefully lead to more durable responses, or maybe even cures, in MM.

New Molecular Technologies for Minimal Residual Disease Evaluation in B-Cell Lymphoid Malignancies

The clearance of malignant clonal cells significantly correlates with clinical outcomes in many hematologic malignancies. Accurate and high throughput tools for minimal residual disease (MRD) detection are needed to overcome some drawbacks of standard molecular techniques; such novel tools have allowed for higher sensitivity analyses and more precise stratification of patients, based on molecular response to therapy. In this review, we depict the recently introduced digital PCR and next-generation sequencing technologies, describing their current application for MRD monitoring in lymphoproliferative disorders. Moreover, we illustrate the feasibility of these new technologies to test less invasive and more patient-friendly tissues sources, such as "liquid biopsy".

European Myeloma Network recommendations on tools for the diagnosis and monitoring of multiple myeloma: what to use and when

The diagnosis of multiple myeloma can be challenging, even for experienced physicians, and requires close collaboration between numerous disciplines (orthopedics, radiology, nuclear medicine, radiation therapy, hematology and oncology) before the final diagnosis of myeloma is made. The definition of multiple myeloma is based on the presence of clinical, biochemical, histopathological, and radiological markers of disease. Specific tests are needed both at presentation and during follow-up in order to reach the correct diagnosis and characterize the disease precisely. These tests can also serve prognostic purposes and are useful for follow-up of myeloma patients. Molecular analyses remain pivotal for defining high-risk myeloma and are used in updated patient stratifications, while minimal residual disease assessment via flow cytometry, molecular techniques and radiological approaches provides additional prognostic information on patients' long-term outcome. This pivotal information will guide our future treatment decisions in forthcoming clinical trials. The European Myeloma Network group updated their guidelines on different diagnostic recommendations, which should be of value to enable appropriate use of the recommendations both at diagnosis and during follow-up.

Noninvasive Molecular Monitoring in Multiple Myeloma Patients Using Cell-Free Tumor DNA: A Pilot Study

Novel treatments for multiple myeloma (MM) have increased rates of complete response, raising interest in more accurate methods to evaluate residual disease. Cell-free tumor DNA (cfDNA) analysis may represent a minimally invasive approach complementary to multiparameter flow cytometry (MFC) and molecular methods on bone marrow aspirates. A sequencing approach using the Ion Torrent Personal Genome Machine was applied to identify clonal IGH gene rearrangements in tumor plasma cells (PCs) and in serial plasma samples of 25 patients with MM receiving second-line therapy. The same clonal IGH rearrangement identified in tumor PCs was detected in paired plasma samples, and levels of IGH cfDNA correlated with outcome and mirrored tumor dynamics evaluated using conventional laboratory parameters. In addition, IGH cfDNA levels reflected the number of PCs enumerated by MFC immunophenotyping even in the complete response context. Patients determined by MFC to be free of minimal residual disease were characterized by low frequencies of tumor clonotypes in cfDNA and longer survival. This pilot study supports the clinical applicability of the noninvasive monitoring of tumor levels in plasma samples of patients with MM by IGH sequencing.

Longitudinal Flow Cytometry Identified "Minimal Residual Disease" (MRD) Evolution Patterns for Predicting the Prognosis of Patients with Transplant-Eligible Multiple Myeloma

Many questions about minimal residual disease (MRD) still need to be answered for multiple myeloma (MM). Flow MRD was monitored in 104 consecutive patients with MM after induction and at the 3rd, 6th, 9th, 12th, 18th, and 24th months post-transplant. Four MRD evolution patterns were revealed: Pattern 1 patients had persistent MRD-negative status after post-induction with no progression; pattern 2 patients had MRD-positive status postinduction but became MRD negative within 24 months post-transplant; pattern 3 patients had MRD-negative status postinduction but became MRD positive within 24 months post-transplant; and pattern 4 patients had persistent MRD-positive status after postinduction. Patients with MRD evolution pattern 1 had a better time to progression than did patients with the other evolution patterns (not reached versus not reached, versus 15.4 ± 2.4 months, versus 16.9 ± 3.0 months; log-rank test, P = .003, P = .000, and P = .000, respectively). Patients with MRD pattern 1 had a significantly longer overall survival than did patients with pattern 3 (not reached versus 35.2 ± 18.6 months; log-rank test, P = .000) and pattern 4 (not reached versus 23.8 ± 15.0 months, log-rank test, P = .000) but had a similar overall survival as pattern 2 patients (not reached versus not reached; log-rank test, P = .229). For progressing patients with MRD evolution pattern 2 or 3, the median interval of a sustained MRD-negative status was only 17 months and the median time from MRD reappearance to disease progression was only 4.6 months. A more complete MRD evolution pattern was developed to predict the outcomes for patients with MM. The optimal time of MRD assessment should include postinduction and 3rd and 24th month post-transplant. Regular MRD assessments will help detect relapse early. A sustained negative MRD status should last for at least 24 months.

Remission maintenance treatment options in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) treatment has come a long way in the last two decades, producing increases in tumor control to the point of generating sizeable numbers of patients with undetectable minimal residual disease and creating overall survival benefits in randomized comparisons. Most of this has been achieved by limited-term treatment approaches including chemotherapeutic and immune-therapeutic drugs. More recently, novel therapies targeting signaling pathways essential for the survival of the neoplastic clones have opened avenues that provide disease control in long-term treatment designs, mostly without producing deep remissions. In this disease, where current treatments are largely unable to effect a cure, prolonged therapy designs using maintenance approaches are explored and 5 randomized studies of maintenance have recently been published. This review shall summarize available results from a systematic literature review in a clinical context and outline basic biology principles that should be heeded in this regard.

Methods and role of minimal residual disease after stem cell transplantation

Relapse is the major cause of treatment failure after stem cell transplantation. Despite the fact that relapses occurred even if transplantation was performed in complete remission, it is obvious that minimal residual disease is present though not morphologically evident. Since adaptive immunotherapy by donor lymphocyte infusion or other novel cell therapies as well as less toxic drugs, which can be used after transplantation, the detection of minimal residual disease (MRD) has become a clinical important variable for outcome. Besides the increasing options to treat MRD, the most advanced technologies currently allow to detect residual malignant cells with a sensitivity of 10^-5 to 10^-6.Under the patronage of the European Society for Blood and Marrow Transplantation (EBMT) and the American Society for Blood and Marrow Transplantation (ASBMT) the 3rd workshop was held on 4/5 November 2016 in Hamburg/Germany, with the aim to present an up-to-date status of epidemiology and biology of relapse and to summarize the currently available options to prevent and treat post-transplant relapse. Here the current methods and role of minimal residual disease for myeloid and lymphoid malignancies are summarized.

Time to plateau as a predictor of survival in newly diagnosed multiple myeloma

Response rates in newly diagnosed multiple myeloma have improved dramatically with the introduction of highly effective novel therapies. However, survival in patients achieving optimal responses to initial treatment can vary significantly, and new prognostic indicators are required to improve risk stratification. We investigated the relationship between time to plateau (T_Plat ) and survival in 1099 newly diagnosed patients treated with novel agents at our institution from 2005 to 2015. T_Plat was defined as time from initiation of first-line therapy to best response to first-line therapy. The median T_Plat was 4.9 months (0.7-58.6) and plateau duration was 1.8 years (0.2-11.0). Patients who required > 120 days to achieve a plateau had longer modified overall survival (mOS) and progression free survival (mPFS) calculated from a landmark of best response (P < .001 for both comparisons). Statistically significant improvement in mOS was retained in subgroup analysis based on age and whether patients received upfront autologous hematopoietic stem cell transplantation (ASCT) (P < .001 for all comparisons). Our results suggest that patients who respond more gradually to initial therapy (T_Plat  > 120 days) experience longer survival compared to more rapid responders. Patients with a prolonged T_Plat could represent an "ongoing responder" phenotype that portends a survival advantage independent of treatment with upfront ASCT, depth of response, and biologic markers such as ISS stage and cytogenetic risk.

Tumor suppressor CD99 is downregulated in plasma cell neoplasms lacking CCND1 translocation and distinguishes neoplastic from normal plasma cells and B-cell lymphomas with plasmacytic differentiation from primary plasma cell neoplasms

CD99(MIC2) is a widely expressed cell surface glycoprotein and functions as a tumor suppressor involved in downregulation of SRC family of tyrosine kinase. CD99 expression is tightly regulated through B-cell development. The principal aims of this study were to investigate the clinical utility of CD99 expression (i) in distinguishing normal plasma cells from primary plasma cell neoplasms; (ii) in detection of minimal residual disease in primary plasma cell neoplasms; and (iii) in distinguishing plasma cell component of B-cell lymphomas from primary plasma cell neoplasms. We analyzed expression of CD99 by flow cytometry and immunohistochemistry in lymph nodes, peripheral blood, and bone marrow samples. CD99 showed stage-specific expression with highest expression seen in precursor B and plasma cells. In contrast to the uniform bright expression on normal plasma cells, CD99 expression on neoplastic plasma cells was lost in 39 out of 56 (69.6%) cases. Furthermore, 8 out of 56 samples (14%) showed visibly (>10-fold) reduced CD99 expression. Overall, CD99 expression was informative (absent or visibly dimmer than normal) in 84% of primary plasma cell neoplasm. In the context of minimal residual disease detection, CD99 showed superior utility in separating normal and abnormal plasma cells over currently established antigens CD117, CD81, and CD27 by principal component analysis. Preservation of CD99 expression was strongly associated with cyclin D1 translocation in myeloma (p < 0.05). B-cell lymphomas with plasma cell component could be distinguished from myeloma by CD99 expression. In summary, we established that tumor suppressor CD99 is markedly downregulated in multiple myeloma. The loss is highly specific for identification of abnormal cells in primary plasma cell neoplasms, and can be exploited for diagnostic purposes. The role of CD99 in myeloma pathogenesis requires further investigation.

Diagnosis of Plasma Cell Dyscrasias and Monitoring of Minimal Residual Disease by Multiparametric Flow Cytometry

Plasma cell dyscrasia (PCD) is a heterogeneous disease that has seen a tremendous change in outcomes due to improved therapies. Over the past few decades, multiparametric flow cytometry has played an important role in the detection and monitoring of PCDs. Flow cytometry is a high-sensitivity assay for early detection of minimal residual disease (MRD) that correlates well with progression-free survival and overall survival. Before flow cytometry can be effectively implemented in the clinical setting, sample preparation, panel configuration, analysis, and gating strategies must be optimized to ensure accurate results. Current consensus methods and reporting guidelines for MRD testing are discussed.

Development of an unbiased, semi-automated approach for classifying plasma cell immunophenotype following multicolor flow cytometry of bone marrow aspirates

BACKGROUND

Despite increased usage of multiparameter flow cytometry (MFC) to assess diagnosis, prognosis, and therapeutic efficacy (minimal residual disease, MRD) in plasma cell neoplasms (PCNs), standardization of methodology and data analysis is suboptimal. We investigated the utility of using the mean and median fluorescence intensities (FI) obtained from MFC to objectively describe parameters that distinguish plasma cell (PC) phenotypes.

METHODS

In this retrospective study, flow cytometry results from bone marrow aspirate specimens from 570 patients referred to the Myeloma Institute at UAMS were evaluated. Mean and median FI data were obtained from 8-color MFC of non-neoplastic, malignant, and mixed PC populations using antibodies to CD38, CD138, CD19, CD20, CD27, CD45, CD56, and CD81.

RESULTS

Of 570 cases, 252 cases showed only non-neoplastic PCs, 168 showed only malignant PCs, and 150 showed mixed PC populations. Statistical analysis of median FI data for each CD marker showed no difference in expression intensity on non-neoplastic and malignant PCs, between pure and mixed PC populations. ROC analysis of the median FI of CD expression in non-neoplastic and malignant PCs was used to develop an algorithm to convert quantitative FI values to qualitative assessments including "negative," "positive," "dim," and "heterogeneous" expression.

CONCLUSIONS

FI data derived from 8-color MFC can be used to define marker expression on PCs. Translation of FI data from Infinicyt software to an Excel worksheet streamlines workflow and eliminates transcriptional errors when generating flow reports. © 2018 International Clinical Cytometry Society.

Minimal Residual Disease Detection by Flow Cytometry in Multiple Myeloma: Why and How?

The outlook for myeloma patients has steadily improved with the introduction of newer drug combinations in recent years. Unlike older therapies that largely achieved only modest levels of neoplastic clone reduction, the newer drug combinations have led to deeper suppression of myeloma clones in most patients. Frequently the neoplastic clones become undetectable with traditional disease evaluation approaches. Recent studies using ultrasensitive disease monitoring have demonstrated that patients with disease undetectable by traditional techniques show wide heterogeneity in disease levels varying by several orders of magnitude. Moreover, measurement of the depth of disease suppression even at very low level has emerged as the most powerful prognostication tool in myeloma. Minimal (or measurable) residual disease (MRD) evaluation has also been proposed as a relevant tool in assessment of drug efficacy and in selection of further therapeutic options. In the face of the robust MRD measurement utility data, it has become critical to develop widely applicable disease monitoring techniques that can be applied to more patients in a variety of clinical setting. Both DNA-based and flow cytometry-based approaches have been successfully developed for this purpose achieving sensitivity approaching 1 neoplastic cell in a million. This review article focuses on the theoretical and practical aspects and challenges of deep MRD monitoring in myeloma by flow cytometry. Challenges of flow cytometric disease monitoring in the era of antigen-directed therapy are also discussed.

Cancer Stem Cells (CSCs) in Drug Resistance and their Therapeutic Implications in Cancer Treatment

Cancer stem cells (CSCs), also known as tumor-initiating cells (TICs), are suggested to be responsible for drug resistance and cancer relapse due in part to their ability to self-renew themselves and differentiate into heterogeneous lineages of cancer cells. Thus, it is important to understand the characteristics and mechanisms by which CSCs display resistance to therapeutic agents. In this review, we highlight the key features and mechanisms that regulate CSC function in drug resistance as well as recent breakthroughs of therapeutic approaches for targeting CSCs. This promises new insights of CSCs in drug resistance and provides better therapeutic rationales to accompany novel anticancer therapeutics.

Minimal residual disease after transplantation or lenalidomide-based consolidation in myeloma patients: a prospective analysis

We analyzed 50 patients who achieved at least a very good partial response in the RV-MM-EMN-441 study. Patients received consolidation with autologous stem-cell transplantation (ASCT) or cyclophosphamide-lenalidomide-dexamethasone (CRD), followed by Lenalidomide-based maintenance. We assessed minimal residual disease (MRD) by multi-parameter flow cytometry (MFC) and allelic-specific oligonucleotide real-time quantitative polymerase chain reaction (ASO-RQ-PCR) after consolidation, after 3 and 6 courses of maintenance, and thereafter every 6 months until progression. By MFC analysis, 19/50 patients achieved complete response (CR) after consolidation, and 7 additional patients during maintenance. A molecular marker was identified in 25/50 patients, 4/25 achieved molecular-CR after consolidation, and 3 additional patients during maintenance. A lower MRD value by MFC was found in ASCT patients compared with CRD patients (p=0.0134). Tumor burden reduction was different in patients with high-risk vs standard-risk cytogenetics (3.4 vs 5.2, ln-MFC; 3 vs 6 ln-PCR, respectively) and in patients who relapsed vs those who did not (4 vs 5, ln-MFC; 4.4 vs 7.8 ln-PCR). MRD progression anticipated clinical relapse by a median of 9 months while biochemical relapse by a median of 4 months. MRD allows the identification of a low-risk group, independently of response, and a better characterization of the activity of treatments.

Analysis of long-term survival in multiple myeloma after first-line autologous stem cell transplantation: impact of clinical risk factors and sustained response

The widespread use of high-dose therapy and autologous stem cell transplantation (ASCT) as well as the introduction of novel agents have significantly improved outcomes in multiple myeloma (MM) enabling long-term survival. We here analyze factors influencing survival in 865 newly diagnosed MM patients who underwent first-line ASCT at our center between 1993 and 2014. Relative survival and conditional survival were assessed to further characterize long-term survivors. Achievement of complete response (CR) post-ASCT was associated with prolonged progression-free survival (PFS) in the whole cohort and with significantly superior overall survival (OS) in the subgroup of patients receiving novel agent-based induction therapy. Landmark analyses performed at 1, 3, and 5 years post-ASCT revealed that sustainment of any response had a highly significant influence on survival with no significant differences between sustained CR and sustained inferior responses. Furthermore, outcome was independently improved by administration of maintenance therapy. A subset of patients did experience long-term survival >15 years. However, conditional survival demonstrated a persistent risk of myeloma-associated death and cumulative relative survival curves did not show development of a clear plateau, even in prognostically advantageous groups. In conclusion, in this large retrospective study, sustained response after first-line ASCT was found to be a major prognostic factor for OS independent of depth of sustained response. Administration of maintenance therapy further improved outcome, supporting the hypothesis that interventions to prolong responses achieved post-ASCT may be essential to reach long-term survival, especially in the setting of persisting residual disease.