Elranatamab in relapsed or refractory multiple myeloma: the MagnetisMM-1 phase 1 trial.

Multiple myeloma (MM) is a plasma cell malignancy expressing B cell maturation antigen (BCMA). Elranatamab, a bispecific antibody, engages BCMA on MM and CD3 on T cells. The MagnetisMM-1 trial evaluated its safety, pharmacokinetics and efficacy. Primary endpoints, including the incidence of dose-limiting toxicities as well as objective response rate (ORR) and duration of response (DOR), were met. Secondary efficacy endpoints included progression-free survival (PFS) and overall survival (OS). Eighty-eight patients with relapsed or refractory MM received elranatamab monotherapy, and 55 patients received elranatamab at efficacious doses. Patients had received a median of five prior regimens; 90.9% were triple-class refractory, 29.1% had high cytogenetic risk and 23.6% received prior BCMA-directed therapy. No dose-limiting toxicities were observed during dose escalation. Adverse events included cytopenias and cytokine release syndrome. Exposure was dose proportional. With a median follow-up of 12.0 months, the ORR was 63.6% and 38.2% of patients achieving complete response or better. For responders, the median DOR was 17.1 months. All 13 patients evaluable for minimal residual disease achieved negativity. Even after prior BCMA-directed therapy, 53.8% achieved response. For all 55 patients, median PFS was 11.8 months, and median OS was 21.2 months. Elranatamab achieved durable responses, manageable safety and promising survival for patients with MM. ClinicalTrials.gov Identifier: NCT03269136 .

Elranatamab in relapsed or refractory multiple myeloma: phase 2 MagnetisMM-3 trial results.

Elranatamab is a humanized B-cell maturation antigen (BCMA)-CD3 bispecific antibody. In the ongoing phase 2 MagnetisMM-3 trial, patients with relapsed or refractory multiple myeloma received subcutaneous elranatamab once weekly after two step-up priming doses. After six cycles, persistent responders switched to biweekly dosing. Results from cohort A, which enrolled patients without prior BCMA-directed therapy (n = 123) are reported. The primary endpoint of confirmed objective response rate (ORR) by blinded independent central review was met with an ORR of 61.0% (75/123); 35.0% ≥complete response. Fifty responders switched to biweekly dosing, and 40 (80.0%) improved or maintained their response for ≥6 months. With a median follow-up of 14.7 months, median duration of response, progression-free survival and overall survival (secondary endpoints) have not been reached. Fifteen-month rates were 71.5%, 50.9% and 56.7%, respectively. Common adverse events (any grade; grade 3-4) included infections (69.9%, 39.8%), cytokine release syndrome (57.7%, 0%), anemia (48.8%, 37.4%), and neutropenia (48.8%, 48.8%). With biweekly dosing, grade 3-4 adverse events decreased from 58.6% to 46.6%. Elranatamab induced deep and durable responses with a manageable safety profile. Switching to biweekly dosing may improve long-term safety without compromising efficacy. ClinicalTrials.gov identifier: NCT04649359 .

CORP: Sources and degrees of variability in whole animal intermittent hypoxia experiments.

Chamber exposures are commonly used to evaluate the physiological and pathophysiological consequences of intermittent hypoxia in animal models. Researchers in this field use both commercial and custom-built chambers in their experiments. The purpose of this Cores of Reproducibility in Physiology paper is to demonstrate potential sources of variability in these systems that researchers should consider. Evaluating the relationship between arterial oxygen saturation and inspired oxygen concentration, we found that there are important sex-dependent differences in the commonly used C57BL6/J mouse model. The time delay of the oxygen sensor that provides feedback to the system during the ramp-down and ramp-up phases was different, limiting the number of cycles per hour that can be conducted and the overall stability of the oxygen concentration. The time to reach the hypoxic and normoxic hold stages, and the overall oxygen concentration, were impacted by the cycle number. These variables were further impacted by whether there are animals present in the chamber, highlighting the importance of verifying the cycling frequency with animals in the chamber. At ≤14 cycles/h, instability in the chamber oxygen concentration did not impact arterial oxygen saturation but may be important at higher cycle numbers. Taken together, these data demonstrate the important sources of variability that justify reporting and verifying the target oxygen concentration, cycling frequency, and arterial oxygen concentration, particularly when comparing different animal models and chamber configurations.NEW & NOTEWORTHY Intermittent hypoxia exposures are commonly used in physiology and many investigators use chamber systems to perform these studies. Because of the variety of chamber systems and protocols used, it is important to understand the sources of variability in intermittent hypoxia experiments that can impact reproducibility. We demonstrate sources of variability that come from the animal model, the intermittent hypoxia protocol, and the chamber system that can impact reproducibility.

Sex differences in cardiovascular disease and dysregulation in Down syndrome.

This meta-analysis, which consisted of a scoping review and retrospective medical record review, is focused on potential sex differences in cardiovascular diseases in patients with Down syndrome. We limited our review to peer-reviewed, primary articles in the English language, in the PubMed and Web of Science databases from 1965 to 2021. Guidelines for scoping reviews were followed throughout the process. Four categorical domains were identified and searched using additional keywords: 1) congenital heart disease, 2) baseline physiology and risk factors, 3) heart disease and hypertension, and 4) stroke and cerebrovascular disease. Articles were included if they reported male and female distinct data, participants with Down syndrome, and one of our keywords. The retrospective medical record review was completed using 75 participating health care organizations to identify the incidence of congenital and cardiovascular diseases and to quantify cardiovascular risk factors in male and female patients. Female patients with Down syndrome are at higher risk of hypertension, ischemic heart disease, and cerebrovascular disease. The risk of congenital heart disease is higher in males with Down syndrome at all ages included in our analyses. Some of the male-to-female sex differences in cardiovascular disease risk in the general patient population are not present, or reversed in the Down syndrome population. This information should be considered for future investigations and ongoing patient care.NEW & NOTEWORTHY In patients with Down syndrome (DS), CHD is the leading cause of death <20 yr old and cardiovascular disease is a leading cause of death in individuals >20 yr old. Men with DS live longer than women. It is unknown if sex differences are present in cardiovascular disease and dysregulation in DS across the lifespan. We observed higher risk of hypertension, ischemic heart disease, and cerebrovascular disease in females and a higher risk of CHD in males with DS.

Acute myeloid leukemia resistant to venetoclax-based therapy: What does the future hold?

Venetoclax is a highly selective B-cell lymphoma-2 (BCL-2) inhibitor, which, combined with a DNA hypomethylating agent or low dose cytarabine, results in high rates of initial responses in patients with acute myeloid leukemia (AML). However, the disease relapses in most patients. Mechanisms of resistance to venetoclax-based therapy include TP53 gene mutations or inactivation of p53 protein, activating kinase mutations such as FLT3 and RAS, and upregulation of other BCL-2 family apoptotic proteins. Current clinical trials are exploring strategies such as doublet or triplet regimens incorporating a p53 activator, an anti-CD47 antibody, or other novel agents that target genes and proteins responsible for resistance to venetoclax. Further studies should focus on identifying predictive biomarkers of response to venetoclax-based therapy and incorporating immunotherapeutic approaches such as checkpoint inhibitors, bispecific antibodies, antibody-drug conjugates, and CAR T-cell therapy to improve outcomes for patients with AML.

Case Studies in Physiology: Untangling the cause of hypoxemia in a patient with obesity with acute leukemia.

Diagnosing the cause of hypoxemia and dyspnea can be complicated in complex patients with multiple comorbidities. This "Case Study in Physiology" describes an man with obesity admitted to the hospital for relapse of acute lymphoblastic leukemia, who experienced progressive hypoxemia, shortness of breath, and dyspnea on exertion during his hospitalization. After initial empirical treatment with diuresis and antibiotics failed to improve his symptoms and because an arterial blood gas measurement was not readily available, we applied a novel, recently described physiological method to estimate the arterial partial pressure of oxygen from the peripheral saturation measurement and calculate the alveolar-arterial oxygen difference to discern the source of his hypoxemia and dyspnea. Using basic physiological principles, we describe how hypoventilation, anemia, and the use of a ß blocker and furosemide, collaborated to create a "perfect storm" in this patient that impaired oxygen delivery and limited utilization. This case illustrates the application of innovative physiology methodology in medicine and provides a strong rationale for continuing to integrate physiology education in medical education.NEW & NOTEWORTHY Discerning the cause of dyspnea and hypoxemia in complex patients can be difficult. We describe the "real world" application of an innovative methodology to untangle the underlying physiology in a patient with multiple comorbidities. This case further demonstrates the importance of applying physiology to interrogate the underlying cause of a patient's symptoms when treatment based on probability fails.

Wearable Monitors Facilitate Exercise in Adult and Pediatric Stem Cell Transplant.

Hematopoietic stem cell transplant (HSCT) is a potentially curative treatment for hematopoietic malignancies, complicated by decreased performance status and quality of life. Exercise therapy improves outcomes in HSCT, but several barriers have prevented exercise from becoming routine clinical practice. Based on existing data that wearable technologies facilitate exercise participation in other sedentary and chronic illness populations, we propose the novel hypothesis that wearable technologies are a valuable tool in transcending barriers and developing exercise therapy programs for HSCT patients.

Chronic intermittent hypoxia enhances disease progression in myeloma-resistant mice.

Obesity is the only known modifiable risk factor for multiple myeloma (MM), an incurable cancer of bone marrow plasma cells. The mechanism linking the two is unknown. Obesity is associated with an increased risk of sleep apnea, which results in chronic intermittent hypoxia (CIH), and drives solid tumor aggressiveness. Given the link between CIH and solid tumor progression, we tested the hypothesis that CIH drives the proliferation of MM cells in culture and their engraftment and progression in vivo. Malignant mouse 5TGM1 cells were cultured in CIH, static hypoxia, or normoxia as a control in custom, gas-permeable plates. Typically MM-resistant C57BL/6J mice were exposed to 10 h/day CIH (AHI = 12/h), static hypoxia, or normoxia for 7 days, followed by injection with 5TGM1 cells and an additional 28 days of exposure. CIH and static hypoxia slowed the growth of 5TGM1 cells in culture. CIH-exposed mice developed significantly more MM than controls (67 vs. 12%, P = 0.005), evidenced by hindlimb paralysis, gammopathy, bone lesions, and bone tumor formation. Static hypoxia was not a significant driver of MM progression and did not reduce survival (P = 0.117). Interestingly, 5TGM1 cells preferentially engrafted in the bone marrow and promoted terminal disease in CIH mice, despite a lower tumor burden, compared with the positive controls. These first experiments in the context of hematological cancer demonstrate that CIH promotes MM through mechanisms distinct from solid tumors and that sleep apnea may be a targetable risk factor in patients with or at risk for blood cancer.

Elevated IgM and abnormal free light chain ratio are increased in relatives from high-risk chronic lymphocytic leukemia pedigrees.

Abnormal serum immunoglobulin (Ig) free light chains (FLC) are established biomarkers of early disease in multiple B-cell lymphoid malignancies, including chronic lymphocytic leukemia (CLL). Heavy chains have also been shown to be biomarkers in plasma cell disorders. An unanswered question is whether these Ig biomarkers are heritable, i.e., influenced by germline factors. CLL is heritable but highly heterogeneous. Heritable biomarkers could elucidate steps of disease pathogenesis that are affected by germline factors, and may help partition heterogeneity and identify genetic pleiotropies across malignancies. Relatives in CLL pedigrees present an opportunity to identify heritable biomarkers. We compared FLCs and heavy chains between relatives in 23 high-risk CLL pedigrees and population controls. Elevated IgM (eIgM) and abnormal FLC (aFLC) ratio was significantly increased in relatives, suggesting that these Ig biomarkers are heritable and could offer risk stratification in pedigree relatives. Within high-risk CLL pedigrees, B-cell lymphoid malignancies were five times more prevalent in close relatives of individuals with eIgM, prostate cancer was three times more prevalent in relatives of individuals with aFLC, and monoclonal B-cell lymphocytosis increased surrounding individuals with normal Ig levels. These different clustering patterns suggest Ig biomarkers have the potential to partition genetic heterogeneity in CLL and provide insight into distinct heritable pleiotropies associated with CLL.

The snoRNA target of t(4;14) in multiple myeloma regulates ribosome biogenesis.

The orphan small nucleolar RNA (snoRNA) ACA11 is overexpressed as a result of the t(4;14) chromosomal translocation in multiple myeloma (MM), increases reactive oxygen species, and drives cell proliferation. Like other snoRNAs, ACA11 is predominantly localized to a sub-nuclear organelle, the nucleolus. We hypothesized that increased ACA11 expression would increase ribosome biogenesis and protein synthesis. We found that ACA11 overexpression in MM cells increased nucleolar area and number as well as silver-binding nucleolar organizing regions (AgNORs). Supporting these data, samples from t(4;14)-positive patients had higher AgNORs scores than t(4;14)-negative samples. ACA11 also upregulated ribosome production, pre-47S rRNA synthesis, and protein synthesis in a ROS-dependent manner. Lastly, ACA11 overexpression enhanced the response to proteasome inhibitor in MM cells, while no effect was found in response to high doses of melphalan. Together, these data demonstrate that ACA11 stimulates ribosome biogenesis and influences responses to chemotherapy. ACA11 may be a useful target to individualize the treatment for t(4;14)-positive myeloma patients.

Prevention Is the Best Treatment: The Case for Understanding the Transition from Monoclonal Gammopathy of Undetermined Significance to Myeloma.

Multiple myeloma is an invariably fatal cancer of plasma cells. Despite tremendous advances in treatment, this malignancy remains incurable in most individuals. We postulate that strategies aimed at prevention have the potential to be more effective in preventing myeloma-related death than additional pharmaceutical strategies aimed at treating advanced disease. Here, we present a rationale for the development of prevention therapy and highlight potential target areas of study.

A multiple myeloma-specific capture sequencing platform discovers novel translocations and frequent, risk-associated point mutations in IGLL5.

Multiple myeloma (MM) is a disease of copy number variants (CNVs), chromosomal translocations, and single-nucleotide variants (SNVs). To enable integrative studies across these diverse mutation types, we developed a capture-based sequencing platform to detect their occurrence in 465 genes altered in MM and used it to sequence 95 primary tumor-normal pairs to a mean depth of 104×. We detected cases of hyperdiploidy (23%), deletions of 1p (8%), 6q (21%), 8p (17%), 14q (16%), 16q (22%), and 17p (4%), and amplification of 1q (19%). We also detected IGH and MYC translocations near expected frequencies and non-silent SNVs in NRAS (24%), KRAS (21%), FAM46C (17%), TP53 (9%), DIS3 (9%), and BRAF (3%). We discovered frequent mutations in IGLL5 (18%) that were mutually exclusive of RAS mutations and associated with increased risk of disease progression (p = 0.03), suggesting that IGLL5 may be a stratifying biomarker. We identified novel IGLL5/IGH translocations in two samples. We subjected 15 of the pairs to ultra-deep sequencing (1259×) and found that although depth correlated with number of mutations detected (p = 0.001), depth past ~300× added little. The platform provides cost-effective genomic analysis for research and may be useful in individualizing treatment decisions in clinical settings.

Computational Model of Progression to Multiple Myeloma Identifies Optimum Screening Strategies.

PURPOSE: Recent advances have uncovered therapeutic interventions that might reduce the risk of progression of premalignant diagnoses, such as monoclonal gammopathy of undetermined significance (MGUS) to multiple myeloma (MM). It remains unclear how to best screen populations at risk and how to evaluate the ability of these interventions to reduce disease prevalence and mortality at the population level. To address these questions, we developed a computational modeling framework. MATERIALS AND METHODS: We used individual-based computational modeling of MGUS incidence and progression across a population of diverse individuals to determine best screening strategies in terms of screening start, intervals, and risk-group specificity. Inputs were life tables, MGUS incidence, and baseline MM survival. We measured MM-specific mortality and MM prevalence after MGUS detection from simulations and mathematic modeling predictions. RESULTS: Our framework is applicable to a wide spectrum of screening and intervention scenarios, including variation of the baseline MGUS to MM progression rate and evolving MGUS, in which progression increases over time. Given the currently available point estimate of progression risk reduction to 61% risk, starting screening at age 55 years and performing follow-up screening every 6 years reduced total MM prevalence by 19%. The same reduction could be achieved with starting screening at age 65 years and performing follow-up screening every 2 years. A 40% progression risk reduction per patient with MGUS per year would reduce MM-specific mortality by 40%. Specifically, screening onset age and screening frequency can change disease prevalence, and progression risk reduction changes both prevalence and disease-specific mortality. Screening would generally be favorable in high-risk individuals. CONCLUSION: Screening efforts should focus on specifically identified groups with high lifetime risk of MGUS, for which screening benefits can be significant. Screening low-risk individuals with MGUS would require improved preventions.

Sabotaging of the oxidative stress response by an oncogenic noncoding RNA.

Overexpression of the multiple myeloma set domain (MMSET) Wolf-Hirschhorn syndrome candidate 1 gene, which contains an orphan box H/ACA class small nucleolar RNA, ACA11, in an intron, is associated with several cancer types, including multiple myeloma (MM). ACA11 and MMSET are overexpressed cotranscriptionally as a result of the t(4;14) chromosomal translocation in a subset of patients with MM. RNA sequencing of CD138+ tumor cells from t(4;14)-positive and -negative MM patient bone marrow samples revealed an enhanced oxidative phosphorylation mRNA signature. Supporting these data, ACA11 overexpression in a t(4;14)-negative MM cell line, MM1.S, demonstrated enhanced reactive oxygen species (ROS) levels. In addition, an enhancement of cell proliferation, increased soft agar colony size, and elevated ERK1/2 phosphorylation were observed. This ACA11-driven hyperproliferative phenotype depended on increased ROS levels as exogenously added antioxidants attenuate the increased proliferation. A major transcriptional regulator of the cellular antioxidant response, nuclear factor (erythroid-derived 2)-like 2 (NRF2), shuttled to the nucleus, as expected, in response to ACA11-driven increases in ROS; however, transcriptional up-regulation of some of NRF2's antioxidant target genes was abrogated in the presence of ACA11 overexpression. These data show for the first time that ACA11 promotes proliferation through inhibition of NRF2 function resulting in sustained ROS levels driving cancer cell proliferation.-Mahajan, N., Wu, H.-J., Bennett, R. L., Troche, C., Licht, J. D., Weber, J. D., Maggi, L. B., Jr., Tomasson, M. H. Sabotaging of the oxidative stress response by an oncogenic noncoding RNA.

TP53 and Decitabine in Acute Myeloid Leukemia and Myelodysplastic Syndromes.

BACKGROUND: The molecular determinants of clinical responses to decitabine therapy in patients with acute myeloid leukemia (AML) or myelodysplastic syndromes (MDS) are unclear. METHODS: We enrolled 84 adult patients with AML or MDS in a single-institution trial of decitabine to identify somatic mutations and their relationships to clinical responses. Decitabine was administered at a dose of 20 mg per square meter of body-surface area per day for 10 consecutive days in monthly cycles. We performed enhanced exome or gene-panel sequencing in 67 of these patients and serial sequencing at multiple time points to evaluate patterns of mutation clearance in 54 patients. An extension cohort included 32 additional patients who received decitabine in different protocols. RESULTS: Of the 116 patients, 53 (46%) had bone marrow blast clearance (<5% blasts). Response rates were higher among patients with an unfavorable-risk cytogenetic profile than among patients with an intermediate-risk or favorable-risk cytogenetic profile (29 of 43 patients [67%] vs. 24 of 71 patients [34%], P<0.001) and among patients with TP53 mutations than among patients with wild-type TP53 (21 of 21 [100%] vs. 32 of 78 [41%], P<0.001). Previous studies have consistently shown that patients with an unfavorable-risk cytogenetic profile and TP53 mutations who receive conventional chemotherapy have poor outcomes. However, in this study of 10-day courses of decitabine, neither of these risk factors was associated with a lower rate of overall survival than the rate of survival among study patients with intermediate-risk cytogenetic profiles. CONCLUSIONS: Patients with AML and MDS who had cytogenetic abnormalities associated with unfavorable risk, TP53 mutations, or both had favorable clinical responses and robust (but incomplete) mutation clearance after receiving serial 10-day courses of decitabine. Although these responses were not durable, they resulted in rates of overall survival that were similar to those among patients with AML who had an intermediate-risk cytogenetic profile and who also received serial 10-day courses of decitabine. (Funded by the National Cancer Institute and others; ClinicalTrials.gov number, NCT01687400 .).

A Meta-analysis of Multiple Myeloma Risk Regions in African and European Ancestry Populations Identifies Putatively Functional Loci.

BACKGROUND: Genome-wide association studies (GWAS) in European populations have identified genetic risk variants associated with multiple myeloma. METHODS: We performed association testing of common variation in eight regions in 1,318 patients with multiple myeloma and 1,480 controls of European ancestry and 1,305 patients with multiple myeloma and 7,078 controls of African ancestry and conducted a meta-analysis to localize the signals, with epigenetic annotation used to predict functionality. RESULTS: We found that variants in 7p15.3, 17p11.2, 22q13.1 were statistically significantly (P < 0.05) associated with multiple myeloma risk in persons of African ancestry and persons of European ancestry, and the variant in 3p22.1 was associated in European ancestry only. In a combined African ancestry-European ancestry meta-analysis, variation in five regions (2p23.3, 3p22.1, 7p15.3, 17p11.2, 22q13.1) was statistically significantly associated with multiple myeloma risk. In 3p22.1, the correlated variants clustered within the gene body of ULK4 Correlated variants in 7p15.3 clustered around an enhancer at the 3' end of the CDCA7L transcription termination site. A missense variant at 17p11.2 (rs34562254, Pro251Leu, OR, 1.32; P = 2.93 × 10-7) in TNFRSF13B encodes a lymphocyte-specific protein in the TNF receptor family that interacts with the NF-κB pathway. SNPs correlated with the index signal in 22q13.1 cluster around the promoter and enhancer regions of CBX7 CONCLUSIONS: We found that reported multiple myeloma susceptibility regions contain risk variants important across populations, supporting the use of multiple racial/ethnic groups with different underlying genetic architecture to enhance the localization and identification of putatively functional alleles. IMPACT: A subset of reported risk loci for multiple myeloma has consistent effects across populations and is likely to be functional. Cancer Epidemiol Biomarkers Prev; 25(12); 1609-18. ©2016 AACR.

Collaborative Control of Cell Cycle Progression by the RNA Exonuclease Dis3 and Ras Is Conserved Across Species.

Dis3 encodes a conserved RNase that degrades or processes all RNA species via an N-terminal PilT N terminus (PIN) domain and C-terminal RNB domain that harbor, respectively, endonuclease activity and 3'-5' exonuclease activity. In Schizosaccharomyces pombe, dis3 mutations cause chromosome missegregation and failure in mitosis, suggesting dis3 promotes cell division. In humans, apparently hypomorphic dis3 mutations are found recurrently in multiple myeloma, suggesting dis3 opposes cell division. Except for the observation that RNAi-mediated depletion of dis3 function drives larval arrest and reduces tissue growth in Drosophila, the role of dis3 has not been rigorously explored in higher eukaryotic systems. Using the Drosophila system and newly generated dis3 null alleles, we find that absence of dis3 activity inhibits cell division. We uncover a conserved CDK1 phosphorylation site that when phosphorylated inhibits Dis3's exonuclease, but not endonuclease, activity. Leveraging this information, we show that Dis3's exonuclease function is required for mitotic cell division: in its absence, cells are delayed in mitosis and exhibit aneuploidy and overcondensed chromosomes. In contrast, we find that modest reduction of dis3 function enhances cell proliferation in the presence of elevated Ras activity, apparently by accelerating cells through G2/M even though each insult by itself delays G2/M. Additionally, we find that dis3 and ras genetically interact in worms and that dis3 can enhance cell proliferation under growth stimulatory conditions in murine B cells. Thus, reduction, but not absence, of dis3 activity can enhance cell proliferation in higher organisms.

Myeloma Cell Dynamics in Response to Treatment Supports a Model of Hierarchical Differentiation and Clonal Evolution.

PURPOSE: Since the pioneering work of Salmon and Durie, quantitative measures of tumor burden in multiple myeloma have been used to make clinical predictions and model tumor growth. However, such quantitative analyses have not yet been performed on large datasets from trials using modern chemotherapy regimens. EXPERIMENTAL DESIGN: We analyzed a large set of tumor response data from three randomized controlled trials of bortezomib-based chemotherapy regimens (total sample size n = 1,469 patients) to establish and validate a novel mathematical model of multiple myeloma cell dynamics. RESULTS: Treatment dynamics in newly diagnosed patients were most consistent with a model postulating two tumor cell subpopulations, "progenitor cells" and "differentiated cells." Differential treatment responses were observed with significant tumoricidal effects on differentiated cells and less clear effects on progenitor cells. We validated this model using a second trial of newly diagnosed patients and a third trial of refractory patients. When applying our model to data of relapsed patients, we found that a hybrid model incorporating both a differentiation hierarchy and clonal evolution best explains the response patterns. CONCLUSIONS: The clinical data, together with mathematical modeling, suggest that bortezomib-based therapy exerts a selection pressure on myeloma cells that can shape the disease phenotype, thereby generating further inter-patient variability. This model may be a useful tool for improving our understanding of disease biology and the response to chemotherapy regimens. Clin Cancer Res; 22(16); 4206-14. ©2016 AACR.