Autologous HSCT with novel agent-based induction and consolidation followed by lenalidomide maintenance for untreated multiple myeloma

2.1 Patients and eligibility

A total of 143 patients from 44 institutions were enrolled in this study between March 2017 and July 2019 after providing written informed consent. The Kyushu University Hospital Institutional Review Board approved the study (approval number; 20181005, UMIN registration number; 000024165), which was conducted by the Japan Study Group for Cell Therapy and Transplantation.

The inclusion criteria for this study were as follows: patients with NDMM as per the International Myeloma Working Group (IMWG) criteria; aged between 20 and 65 years; measurable levels of serum and/or urinary M-protein; Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0–2 (grades 3–4 acceptable if pain is caused by myeloma); adequate hematological parameters (e.g., absolute neutrophil count [ANC] ≥1.0 × 10⁹/L, hemoglobin level ≥8 g/dL without transfusion, platelet count ≥75 × 10⁹/L); creatinine clearance (CCr) ≥30 mL/min estimated by the Cockcroft–Gault formula; serum total bilirubin level ≤1.5 times the upper limit of normal (ULN); levels of aspartate aminotransferase (AST) and/or alanine aminotransferase (ALT) values ≤3 × ULN; left ventricular ejection fraction ≥50%; oxygen saturation ≥93% measured by pulse oximetry in room air; expected prognosis of more than 3 months; adequate contraception available. Patients were excluded if they had myeloma-related disorders (e.g., solitary plasmacytoma, plasma cell leukemia, Waldenstrom's macroglobulinemia, amyloidosis, POEMS syndrome), recent treatment history (surgery, radiation, and ≥30 mg/day of corticosteroids) within the last 14 days, central nervous system invasion, active concurrent malignancies, active systemic infection, positive viral screening tests (hepatitis B surface antigen, hepatitis C antibody, or human immunodeficiency virus), potential pregnancy, or other severe medical or psychiatric conditions unsuitable for study inclusion.

2.2 Protocol

2.3 Peripheral blood stem cell (PBSC) harvest

A mobilization procedure was scheduled for patients with PS 0–2, adequate vital organ functions, and no evidence of progressive disease (PD). For efficient PBSC harvest, high-dose cyclophosphamide was administered (1.5 g/m² × 2 days), combined with four doses of sc Bor (1.3 mg/m² or last tolerated dose [LTD]). Granulocyte colony-stimulating factor was initiated during myelosuppression to mobilize CD34⁺ hematopoietic stem/progenitor cells to peripheral blood. When planning this trial, plerixafor was not yet available. The minimum required amount of collected CD34⁺ cells was 2 × 10⁶ cells per patient body weight, with a second apheresis allowed if the first did not yield enough cells.

2.4 Autologous hematopoietic stem cell transplantation

High-dose chemotherapy with autologous stem cell rescue was performed on patients with PS of 0–2, adequate vital organ functions, no evidence of PD, and preservation of ≥2 × 10⁶/kg of CD34⁺ cells. Patients underwent a conditioning regimen comprising melphalan (Mel) (total dose of 200 mg/m² over two consecutive days) and four doses of sc Bor (1.3 mg/m² or LTD). Reduced Mel dose (total of 140 mg/m²) was adjusted for patients with impaired renal function.

2.5 Consolidation and maintenance therapy

Patients with good PS, adequate vital organ functions, and no PD 90 days post ASCT underwent four consolidation cycles with Cfz (20 mg/m² on days 1 and 2 and 27 mg/m² on days 8, 9, 15, and 16 for the first consolidation course; 27 mg/m² on days 1, 2, 8, 9, 15, and 16 for the subsequent two to four courses, respectively), Len (25 mg/day or LTD on days 1 to 21), and DEX (40 mg/day on days 1, 8, and 15). Subsequently, maintenance with Len monotherapy (10 mg/day or LTD from day 1–21) was continued every 4 weeks until PD.

2.6 Fluorescence in situ hybridization (FISH) analysis

Plasma cells were purified from BM samples of initial diagnosis by using anti-CD138-coated magnetic beads (EasySep Human CD138 Positive Selection Kit, STEMCELL Technologies Inc.). FISH analyses were conducted to detect (i) chromosome 17p deletion (del[17p]), (ii) IgH/FGFR3 fusion due to t(4;14)(p16;q32), (iii) IgH/MAF fusion due to t(14;16)(q32; q23), and (iv) gain of chromosome 1q (1q gain) using commercially available methods (LSI Medience Corporation).

2.7 Minimal/measurable residual disease (MRD) analysis

High-molecular-weight DNA from BM plasma cells was analyzed to identify IgH rearrangements to generate allele-specific oligonucleotide (ASO) primers. MRD analysis was conducted in cases where an ASO primer for IgH-PCR could be established. The sensitivity of our MRD test was 10⁻⁵. We assessed the MRD status post induction therapy, post ASCT, post consolidation therapy, and 1 year after starting maintenance therapy in patients who achieved a very good partial response (VGPR) or better.

2.8 Endpoints

The primary endpoint of this study was the complete response (CR) rate following consolidation therapy with KRD. Secondary endpoints included CR rate post VRD induction therapy, CR rate 100 days post ASCT, stringent CR (sCR) rate post consolidation therapy, CR rate 3 years after treatment protocol initiation, 3-year progression-free survival (PFS), 3-year overall survival (OS), time to treatment failure (TTF), rate of MRD negativity at specific timepoints, and toxicities.

The response to treatment was assessed according to the IMWG criteria¹⁴ at the appropriate time. The AEs were monitored throughout the study and categorized according to the Common Terminology Criteria for Adverse Events (version 4.0). The treatment was discontinued in cases of unacceptable toxicities, disease progression, patient consent withdrawal, or patient mortality due to any cause.

2.9 Statistics

Progression-free survival, defined as the time from study enrollment to disease progression or death from any cause, OS, defined as the time from study enrollment to death from any cause, and TTF, defined as the time from study enrollment to disease progression, death from any cause, or early treatment discontinuation for any reason, were estimated using the Kaplan–Meier method. The confidence interval (CI) was calculated using Greenwood's formula.

Referring to prior studies^{2, 15-18} by us and others, we set the expected CR rate and the threshold CR rate in this study at 58% and 46%, respectively. The sample size calculation for the study, using a binomial test with normal approximation (one-sided 5% significance level, 80% power), yielded 106 cases. Accounting for a 20% dropout rate after the registration, at least 133 patients were targeted for a reliable statistical analysis. All analyses were conducted using EZR software version 4.0.3 (Saitama Medical Center, Jichi Medical University).¹⁹

3.1 Patients' characteristics

Among 143 enrolled patients, two cases were excluded due to concurrent nonhematologic malignancy or initiation of radiation therapy for oncologic emergency. The baseline characteristics of the remaining 141 patients are presented in Table 1. The median age was 58 years (range, 38–65 years), with 83.7% of patients at PS 0–1. The M-protein class was IgG in 86 (61.0%), IgA in 32 (22.7%), IgD in 2 (1.4%), and Bence Jones in 21 (14.9%). Clinical stage determined by the International Scoring System was I in 60 (42.6%), II in 61 (43.3%), and III in 20 (14.2%). The median plasma cells in the BM at the beginning of the study were 27.4%. Extramedullary disease was observed in 16 (11.3%) patients. Cytogenetic analyses by FISH, feasible in 121 (85.8%) patients, revealed abnormal FGFR3 expression linked to t(4;14) in 17 cases, abnormal expression of the MAF associated with t(14;16) in 3 cases, TP53 impairment related to del 17p in 24 cases, and 1q gain in 51 cases.

Overall, 69 patients (57.0% of those available for analysis) were classified as high-risk cytogenetics, and 21 patients (17.4%) possessed two or more high-risk cytogenetic abnormalities (Table 1).

3.2 Treatment status

Our patients followed the treatment protocol outlined in Figure 1. A total of 121 (85%) patients completed four induction cycles, while 2 experienced PD and 18 withdrew due to AEs (n = 16) or consent withdrawal (n = 2). Of the 121 patients who completed induction, 7 did not proceed to ASCT due to PD (n = 3), AEs (n = 3), or early-stage colorectal cancer detection (n = 1). The median number of collected CD34⁺ cells was 6.40 × 10⁶ (range, 2.0–85.7) cells/kg. Only seven cases required 2 days of apheresis, and no patient failed to reach the target cell count. After ASCT, all patients achieved prompt neutrophil engraftment, with a median of 11 (range, 9–21) days; however, 13 patients exited the protocol due to PD (n = 2), consent withdrawal (n = 2), or not meeting the criteria to start the next treatment (n = 9). Thus, 101 (72%) patients received four consolidation cycles. Subsequently, 85 (60%) patients, excluding 16 who dropped out due to PD (n = 1), AEs (n = 12), or consent withdrawal (n = 2) progressed to maintenance with Len; 71 (50%) patients continued over a year.

3.3 Response assessment

Responses among the intent-to-treat population are summarized in Figure 2. After completing the KRD consolidation therapy, 83 (58.9% [90% CI, 51.6%–65.8%]) patients achieved CR or better, meeting this study's primary endpoint. Response rates continued to improve throughout the treatment protocol. CR/sCR was observed in 28 (19.9%) patients post induction, 41 (29.1%) after PBSC collection, 56 (39.7%) following ASCT, 83 (58.9%) after consolidation, and 88 (62.4%) during maintenance. Overall, 14 patients (9.9%) experienced disease progression during the treatment period. With a median follow-up of 38 months, the 3-year estimates for OS, PFS, and TTF were 92.5% (95% CI, 86.6%–95.9%), 83.5% (95% CI, 76.0%–88.8%), and 42.3% (95% CI, 33.9%–50.4%), respectively (Figure 3).

3.4 Subgroup analysis

We further compared the outcomes among patients with varying cytogenetic risks. Patients with at least one of the following high-risk cytogenetic abnormality (del(17p), t(4;14), t(14;16), or 1q gain) showed a marginal association with lower 3-year PFS compared with those without (77.8% vs. 89.4%, p = 0.051) (Figure 4A). For each high-risk cytogenetic abnormality, del(17p) (p = 0.125), t(4;14) (p = 0.327), or 1q gain (p = 0.119) did not affect 3-year PFS. Patients with t(14;16) had significantly inferior 3-year PFS (p = 0.037), although this abnormality was detected only in three cases (data not shown). Moreover, a statistically significant association was found between ≥2 high-risk cytogenetics and PFS (p = 0.0027, as shown in Figure 4B).

Allele-specific oligonucleotide primer for MRD detection could be established in 106 (75.2%) patients. Among them, we assessed the MRD status upon achieving a VGPR or better. Approximately 60% of patients achieved MRD negativity post induction, increasing to 80% after ASCT and 90% following consolidation/maintenance (data not shown). MRD status after ASCT (pre-consolidation) significantly correlated with improved 2-year PFS (92.3% [95% CI, 82.0%–97.2%] vs. 68.8% [95% CI, 35.7%–87.3%], p = 0.0067) (Figure 4C). Notably, among 30 patients who achieved BM-sustained MRD negativity (≥12 month) in this ASO-PCR method, all but one patient demonstrated durable response with a median 1142 (range, 956–1484) days of PFS (data not shown).

3.5 Safety profile

Regarding safety data, serious AEs of ≥ grade 3 during each treatment were collected and are listed in Table 2. The most common toxicity linked to scVRD induction was skin rash (15.6%), followed by myelosuppression (13.5%), PN (10.6%), elevated liver enzymes (9.2%), and infections (8.5%). A total of 12 patients developed severe and/or persistent PN (≥grade 2) requiring reduction or discontinuation of Bor dosing. Of them, one patient suffered from grade 3 PN and another patient suffered from persistent painful grade 2 PN and discontinued this treatment protocol. During consolidation with KRD, most toxicities were hematologic (34.7%), with only 4% of patients developing PN. Common AEs reported during Len maintenance included myelosuppression (17.6%) and elevated liver enzymes (3.5%). Overall, the treatment protocol was discontinued in 31 (22.0%) patients due to unacceptable AEs, including myelosuppression (n = 9), skin rash (n = 5), PN (n = 4), fever (n = 3), and so on. Half of the AEs that led to protocol discontinuation were during remission induction therapy (n = 16) mainly due to nonhematologic toxicity, followed by those during consolidation therapy (n = 12) mainly due to hematologic toxicity.