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 Table of Contents  
REVIEW ARTICLE
Year : 2018  |  Volume : 1  |  Issue : 1  |  Page : 1-8

A closer look at the bone marrow microenvironment in multiple myeloma


Saskatoon Cancer Centre, College of Medicine, University of Saskatchewan, Saskatoon, Canada

Date of Web Publication30-Jan-2018

Correspondence Address:
Dr. Hadi Goubran
Saskatoon Cancer Centre, College of Medicine, University of Saskatchewan, SK, 20 Campus Road, Saskatoon, SK S7N 4H4
Canada
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2395-7182.203049

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  Abstract 


Multiple myeloma, a plasma cell (PC) neoplasm accounting for nearly 10% of hematologic malignancies, remains an incurable disease of the bone marrow (BM) with a fascinating pathophysiology. The maladaptive nature of myeloma PCs and the BM microenvironment niche has been recognized to play a crucial role in the pathogenesis and progression of the disease which behaves in a manner similar to solid tumors in their growth and dissemination. A complex interaction between osteoclasts, endothelial cells, BM matrix, myeloid as well as the lymphoid elements and the malignant PCs occurs at the level of the microenvironment favoring the expansion of latter cells and their spread. A better understanding of the diseased PC and their milieu will enable the development of novel therapeutic tools capable of improving the outcome of this incurable blood cancer.

Keywords: Bone marrow, microenvironment, multiple myeloma


How to cite this article:
Stakiw J, Bosch M, Goubran H. A closer look at the bone marrow microenvironment in multiple myeloma. Tumor Microenviron 2018;1:1-8

How to cite this URL:
Stakiw J, Bosch M, Goubran H. A closer look at the bone marrow microenvironment in multiple myeloma. Tumor Microenviron [serial online] 2018 [cited 2018 Dec 14];1:1-8. Available from: http://www.TMEResearch.org/text.asp?2018/1/1/1/203049




  Introduction Top


Multiple myeloma (MM) is a plasma cell (PC) malignancy that accounts for <1% of all cancers and for around 10% of hematological malignancies with an estimated incidence of 5.7 per 100,000 in Europe and 5.5 per 100,000 in the US. Worldwide, more than 115,000 new cases are diagnosed each year.[1]

MM is a primary malignancy of the bone marrow (BM) PCs initiated by the transformation of memory B cells (CD19+, CD 27+, CD 38+, the CD45−, and CD 138−)[2] often acquiring a chromosomal translocation into the IgG loci. However, unlike other hematologic malignancies diffusely infiltrating the marrow, it behaves like a tumor metastasis with the involvement of the bone. Osteolytic bone lesions and compression fractures are the hallmark of the disease resulting in its significant morbidity.[3]

MM progresses in the BM under the influence of signals from its microenvironment.


  Normal Bone Marrow Microenvironment Top


The BM contains two types of cells; hematopoietic stem cells (HSCs) and nonhematopoietic cells.

HSCs bears the CD markers: CD34+, CD59+, Thy1/CD90+, CD38lo/−, C-kit/CD117+, and give rise to both the myeloid or lymphoid lineages of blood cells and a third category consisting of balanced HSC. Only the myeloid-biased and -balanced HSCs have durable self-renewal properties. Long-term HSC (LT-HSC) is quiescent and low cycling capable of maintaining hematopoiesis for moths whereas short-term HSC is capable of self-renewal. Both coexist in the BM milieu.

The nonhematopoietic component includes osteoblasts/osteoclasts (OBs/OCs), endothelial cells (ECs), endothelial progenitor cells and mesenchymal stem cells (MSCs)[4] and for classification purposes OCs/OBs, although these cells are derived from hematopoietic progenitors.[5] Together these cells form specialized “niches.” Niches are local tissue microenvironments that maintain and regulate HSCs.[4] Niches with proximity to the vasculature are called vascular niche. Those close to the endosteum are known as OB niche. OB and vascular niches are found adjacent to each other the three dimensional BM microenvironment and interact in very complex and intimate ways.[3],[6],[7] Defining niche components and how they work in concert to regulate hematopoiesis will improve our understanding of how a disordered niche function could contribute to disease.

In addition, the BM microenvironment may also be divided into the cellular compartment, comprised of hematopoietic cells and nonhematopoietic cells and the noncellular compartment where the extracellular matrix (ECM), cytokines and growth factors are present.[8]

Osteoblastic niche

Dating back to early 1970s, it was known that undifferentiated HSC would localize close to the endosteal bone surface forming a “niche.”[9],[10] The main task of the osteoblastic niche is to maintain the LT-HSCs, which are capable of supporting hematopoiesis for months or even a lifetime as quiescent or low-cycling cells.[11],[12],[13],[14] An increase in the number of osteoblastic lining cells in the trabecular bone area is associated and correlates with an increased number of LT-HSCs in vivo.[12],[15]

The osteoblastic niche is also composed of reticular cells, fibroblasts, and adipocytes. These cells create a supportive environmental matrix for stem cells.[16] Data indicate that the endosteal region is important for hematopoiesis.

Mature osteolineage cells have only an indirect role in modulating HSCs.[4] They elaborate cytokines and ECM proteins that influence a wide range of cell types including some HSC functions. This is exemplified by parathyroid hormone receptor activation which induces expression of multiple regulatory molecules (such as interleukin 6 [IL-6], receptor activator of nuclear factor-kappa B ligand [RANKL], and Jagged1) by OBs influencing other cells in the BM, including the vasculature.[11] The endosteal region and its osteoblastic cells, therefore, provide a unique zone for the maintenance of quiescent HSCs.[4]

Osteoblastic niche is also crucial for the support and proliferation of megakaryocytes.[17]

Physiologically, BM adipogenesis occurs in the osteoblatic niche of all mammals. The MSC is the marrow precursor for adipocytes as well as OBs and peroxisome proliferator-activated receptor gamma is an essential differentiation factor for entrance into the fat lineage. Aging, several chronic conditions including diabetes mellitus and osteoporosis as well as malignancy are associated with accelerated marrow adipogenesis.[18]

Vascular niche

The vascular niche was described later than the osteoblastic one. It has been regarded as an alternative and indispensable compartment for the regulation of HSCs.[19] It is through that the interaction of the HSCs and the vascular ECs initiates HSC self-renewal and differentiation.[20],[21],[22] There the quiescent HSCs residing in the osteoblastic niche penetrates the vascular compartment to enter the circulation.[19]

The structure of the vascular niche is rather complex. Sinusoidal vessels are supplied by arterioles and capillaries which are derived from the bifurcation of arteries spanning the marrow cavity.[21] The sinusoids, interconnected by intersinusoidal capillaries drain into the central sinus. Sinusoidal ECs (SECs) play a role both in providing a differentiation platform for hematopoietic cells and as a conduit for their mobilization and homing into and out of the BM.[21],[23] SECs constitute most of the functional hematopoietic vascular niche and are essential in hematopoietic processes and in the maintenance of HSCs which are mobilized from a dormant LT-HSC state.[21],[24] Under stress, or when the BM is infiltrated, LT-HSCs migrate to bloodstream by penetrating the sinusoidal wall and then differentiate into several kinds of blood cells.[25]

If the BM is under stress, extramedullary hematopoiesis within vascular niche occurs in the spleen or liver to supplement the function in abnormal BM [26] thus reinforcing the concept that the vascular niche supports the maintenance and differentiation of HSCs when the BM works abnormally.

A multitude of molecules and ECs secreting factors mediate HSCs self-renewal and regeneration.[19] Stromal cell-derived factor 1 (SDF-1) mediates transendothelial and stromal migration when binding to its receptor (CXCR-4) and is important in megakaryopoiesis.[27] The role played by G-CSF is also medicated by SDF-1.[28] ECs expressing Notch ligands which are relevant for HSC self-renewal in an undifferentiated state, preventing their exhaustion.[29] Vascular cell adhesion molecule 1 (CD106) induces expression of adhesion molecules needed for HSC maintenance.[30] ECs secreting factor also interplays with HSCs with the Stem Cell Factor maintaining HSCs, Glycoprotein 130 contributing to hematopoiesis and pleiotrophin inducing HSC regeneration.[19]


  the Bone Marrow Microenvironment in Multiple Myeloma Top


In MM, osteolytic bone lesions and compression fractures are the hallmark of the disease, causing significant morbidity.[2],[3] Hematopoietic alterations are common as anemia, which is an integral element of the symptomatic myeloma (CRAB: High calcium, renal impairment, anemia, and bone lesions) and occurs in more than 70% of the cases at diagnosis and is the primary cause of the decline in performance status noted by patients.[3]

The main cause of the anemia is replacement of the hematopoietic cells by clonal PCs nests in the process of myelophthisis.[31] The erythroid progenitors overexpressing FAS molecules are more prone to apoptosis and are also affected by the reduced erythropoietin level associated with impaired kidney function.[32],[33] Furthermore, the chronic inflammatory state associated with the activity of the disease results in an altered iron metabolism additionally contributing to the anemia.[33]

Multiple pathogenic mechanisms can contribute to kidney injury in myeloma patients ranging from cast nephropathy to amyloidosis or light chain deposition disease. Many patients have chronic glomerular nephropathy and a substantial proportion may progress to end-stage renal disease.[34]

In the presence of a MM clone nesting in the BM, the tumor cells behave like a classic solid tumor in a microenvironment where stromal factors, immunological factors, humoral, and hormonal factors as well as platelets/microparticles and megakaryocytes interact to favor tumor growth, tethering, and dissemination.[35] The role played by the OCs and the myeloid-derived suppressor cells (MDSCs) are primordial in this respect and mediate the osteolytic bone lesions and hypercalcemia.[36]

The introduction of novel agents including immunomodulatory drugs (thalidomide and lenalidomide) and proteasome inhibitors (bortezomib), have increased the rates of remission in the newly diagnosed MM patient permitting a better prognosis for transplant-eligible patients, and a more prolonged remission when combined with melphalan or other chemotherapeutic agents in the less fortunate transplant noneligible population.[37] In addition, most patients will benefit from bisphosphonates which reduces bone pain and the risks of pathological fractures.[38]

Encouraging reports from ongoing clinical trials focusing primarily on eradication of the malignant myeloma cells, point to extending progression-free and overall survival for MM patients. An increased probability of drug-resistant clones emerging following these therapeutic interventions however, are likely to occur secondary to MM clones undergoing genetic mutations.[39] Targeting the MM BM microenvironment can, therefore, offer a new avenue to address MM. A better understanding of this milieu is accordingly of great importance.


  Bone Marrow Milieu of Multiple Myeloma Top


The BM milieu of MM is comprised ECM, hematopoietic and nonhematopoietic cells as well as soluble components including cytokines, growth factors, and adhesion molecules.[8]

The MM mutated PCs grossly destabilize the normal BM niches and interfere with the complex interaction between myeloid-derived cells and lymphoid-derived immunocompetent cells as well as the matrix cells and their by-products. Abnormal marrow milieu reciprocally enhances abnormal PC proliferation.

Osteoclasts

Interaction and balance between OB and OC cells maintain normal physiologic bone environment. Dysregulation of OBs and OCs serves as the key process in the pathogenesis of myeloma bone disease. Increased OCs activity in MM patients promotes bone absorption, while suppression of OBs activity leads to impaired bone formation.[40],[41] The increased OCs activity is under the influence of a myriad of important OC activating factors (OAFs) isolated from myeloma cell culture medium. These include IL-6, IL-1b, tumor necrosis factor (TNF)-α, and parathyroid hormone-related protein.[42] Other OAFs such as macrophage inflammatory protein-1a, RANK and RANKL, osteoprotegerin and annexin II also play important roles in bone absorption.[43] Myeloma cells promote OC formation through the endogenous expression of RANKL, TNF-α, and the downregulation of RANKL decoy receptor and OPG.[44]

Interestingly, RANKL, a member of TNF superfamily is regulated by a variety of cytokines sand hormones, such as parathyroid hormone, 1, 25-dihydroxy-vitamin D (cholecalciferol), and prostaglandin E2. After the specific binding between RANKL and RANK, their downstream by-products such as TNF receptor associated factor initiate OC generating gene transcription. Ultimately, OC precursor cells evolve into mature OCs.[41] Once generated, OCs form a resorptive seal on the mineralized bone matrix surface and degrade the bone. They often induce micro-cracks by secreting hydrochloric acid and acidophilic collagenases such as cathepsin K.[45] The damaged bone matrix as well as the platelets recruited to the site, secrete transforming growth factor beta (TGF-β) and insulin growth factor I (IGF-I) that will promote myeloma cell growth.[35],[46] Myeloma cells may even fuse with OCs and affect their functionality; 30% of OCs recruited in BM microenvironment of MM patients contain transcriptionally active chromosomes of myeloma origin [47] and myeloma cell/OCs interaction is often partly mediated by IL-6.[48]

The destructive role of the OCs is unopposed by OBs as it was also noted that in the MM BM milieu, OBs inhibitory factors are present including TGF-β. The plasma concentration of IL-3 significantly increases in patients with MM and can not only significantly increase OC activity but also inhibit osteogenic protein-2 (bone morphogenetic protein-2), thereby inhibiting OB differentiation.[49],[50] The net result therefore is the bone destructive process that characterizes myeloma and additional proliferation of the myeloma clone.

Endothelial cells

ECs of the MM BM exhibit enhanced expression of angiogenic factors and their receptors such as vascular endothelial growth factor (VEGF) and VEGF receptor-2, fibroblast growth factor-2 (FGF-2) and FGF-2 receptor-2, Ang-2 and Tie-2. By increased in vitro and in vivo angiogenic activity, ECs maintains adequate blood supply to the growing MM clone and help its spread.[51] Moreover, MM ECs express more mRNA and secrete larger amounts of the CXC-chemokines, interferon-inducible T-cell alpha, and monocyte chemoattractant than umbilical vein ECs.[52] Circulating ECs were six-fold higher in peripheral blood of MM patients compared to controls and correlated positively with serum M protein and β2-microglobulin.[53] Furthermore, platelet-derived growth factor (PDGF)-receptor beta (PDGFR-β) is expressed by ECs isolated from MM patients.[52] PDGF-BB/PDGFR-β kinase axis promotes MM vessel sprouting and the transcription of MM ECs-released VEGF and IL-8.[54] Finally, the role played by the platelet-endothelial interaction in the tumor milieu, with the P-selectin acting as a key molecule, is crucial for tumor spread and dissemination.[35]

Myeloid cells

The bone microenvironment where myeloma cell nests are growing is studded by immune competent cells. Immature myeloid cells present in the BM differentiate into macrophages, dendritic cells (DCs), and granulocytes. Under the influence of certain tumor-derived growth factors, differentiation is halted and a rapid expansion of immature myeloid cells (often termed MDSCs) which fail to differentiate, interfere with the immune surveillance and contribute to the tumor growth. Myeloid DCs (MDCs) are potential therapeutic targets in myeloma.[36] Görgün et al., assessed the presence, frequency, and functional characteristics of MDSCs in patients with newly diagnosed, relapsed, and relapsed/refractory MM compared with healthy donors and the immunomodulatory effects of novel therapies on this cellular subset. CD11b1CD14-HLA-DR-/lowCD331CD151 MDSCs were significantly increased in both the peripheral blood and the BM of patients with active MM compared with healthy donors. A bidirectional interaction between MDSCs and MM cells and immune effector cells was noted.[55] Furthermore, Malek et al., demonstrated that MDSCs and T regulatory cells (Tregs) are significantly increased in myeloma patients and their levels correlate with disease stage and clinical outcome. MDSCs can therefore mediate suppression of myeloma-specific T-cell responses through the induction of T-cell anergy and promotion of Tregs in the MM microenvironment.[56]

Monocytes are attracted to the tumor milieu by certain chemokines including the CXCR4/CXCL12 axis.[57] A wide range of growth factors and cytokines VEGF and endothelin-2 are thought to educate the macrophages and determine their role as tumoricidal or tumor promoters.[58] Macrophages of the M1 population producing pro-inflammatory cytokines such as TNF-α, IL-1, and IL-12 are tumoricidal/static. These cells can be polarized to an M2 population, acting as tumor promoters and are capable of producing IL-6 needed for the growth of myeloma cells, and IL-10 which further polarizes more M1–M2.[59] Repolarizing M2–M1 or depletion of the M2 population are interesting therapeutic strategies.[60]

DCs, also known as accessory cells, are the major antigen processing and presenting cells in the tumor milieu. DCs usually act as the link between the innate and the adaptive immune systems, presenting the antigen on their surface to the recruited T-cells.[61] The number of plasmoid DCs is significantly increased in the BM of myeloma patients compared to healthy individuals and patients with MGUS with only a modest increase in peripheral blood.[62],[63] DCs have conflicting opposing actions on myeloma cells; on one side, they activate CD8(+) T cells against tumor PCs and on the other, they protect tumor PCs from CD8(+) T-cell killing.[63] Functionally, DCs overexpress activation of B-cell maturation antigen by its ligand, a proliferation-inducing ligand (APRIL) and inhibit RANKL to promote human MM progression in vivo. They can target MM cells harboring p53 mutation in mice.[64] In the MM BM microenvironment, DCs engulf apoptotic MM cells through CD91, and their antigen is presented in the context of a MHC-class I antigen to activate CD8+ ve cells. Using the CD80/CD86 pathway, DCs interact with MM cells overexpressing CD28 resulting in a proteasome degradation that will impair antigen expression, helping MM cells escape the T cell recognition and killing. Furthermore, checkpoint inhibitors such as programmed cell death 1 (PD-1) partially offset immunosuppressive signals from the marrow microenvironment as The majority of PC and DCs subpopulations express PD-1 and a correlation between the proportion of PD-1+ PC and CD141+ mDC has been demonstrated, suggesting both cell types could down-regulate the anti-tumor T cell response.[65],[66] DCs also significantly contribute to the lytic lesions of MM by differentiating into OCs under the influence of IL-17A.[67],[68]

Although best known for their role in allergy and anaphylaxis, mast cells play an important protective role and are intimately involved in angiogenesis and immune tolerance. Their density in the MM BM correlates with circulating levels of various angiogenic factors crucial for the maintenance of blood supply to the MM cell population, namely VEGF, angiopoietin 2, and angiogenin. In addition, their matrix metalloproteinase 9 (MMP-9) is involved in the degradation of the ECM [69] and IL-6 stimulated MM cells which protect them from spontaneous or drug-induced apoptosis.[70] Interestingly, the density of mast cells in the BM of MM patients correlates with the proliferation index Ki-67.[71]

The role played by the megakaryocytes, platelets, and their derived microparticles in the progression of solid tumors and their metastatic seeding have long been recognized.[35],[72],[73],[74],[75],[76]

BM PC tumors are supported by the external growth factors APRIL and IL-6, among others. Recently, eosinophils and megakaryocytes were shown to be functional components of the microenvironmental niches of benign BM PCs and to be important local sources of these cytokines in addition it supports the growth of tumor PCs in the MOPC315.BM model for MM.[77]

Lymphoid cells

Although MM is derived from PC of B cell origin, other B as well as T lymphocytes and natural killer cells (NK) interplay in the MM BM microenvironment favoring tumor growth and tethering.[36]

T-cells expressing the T-cell receptors have a distinct function in the fight against cancer and myeloma in particular. A regulatory subset of CD8+ T cells has been identified in myeloma microenvironment, suppressing CD4+-cell proliferation by producing interferon gamma contributing to the immunosuppression seen in myeloma.[36] The T-cell activity can also be suppressed by the activation of a number of receptors on their surface including PD-1 receptor with its ligand being overexpressed by myeloma cells.[65]

Tregs are developed from CD4 T-cells under the influence of local cytokine production in the MM milieu and are significantly increased in myeloma patients and their levels correlate with disease stage and clinical outcome.[55] The balance between Th1 and Th2 seems also to be altered in the MM milieu with reduced Th1 cytokines and over-expression of Th2 cytokines namely IL-10 and IL-4.[78]

Th17 produce IL-17 that plays a pivotal role in bone disease and 22. PCs express IL-17 receptor on their surface. Th17 are predictive factors of response to therapy in MM and their expansion suppresses immune responses and protect PCs from the T-cell surveillance.[78]

B-cells, on the other hand, results in the formation of the terminally differentiated, antibody-producing PCs.[2] Symptomatic myeloma patients have less B-cell, particularly memory B-cells, compared to healthy individuals or patients with early disease and contribute to the increased frequency of infection among patients.[36]

The decreased NK activity in the MM microenvironment is also contributing to the progression of the disease and are affected by novel therapeutic agents that enhance their function.[36]

[Figure 1] illustrates the interaction of MM PCs with different myeloid and lymphoid cells and the role played by MDCs.
Figure 1: Myeloid precursors fail to differentiate under the effect of the growing myeloma cells with the accumulation of immature myeloid-derived suppressor cells. Furthermore, Macrophages are polarized to M2 favoring tumor growth and dendritic cells engulfing apoptotic plasma cells have an impaired antigen expression potential. Myeloid-derived suppressor cells also favor the transition of T cells to T-regulatory cells

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In MM, a significant interaction between the different components of the BM niches takes place. The myeloma-PC dysregulate the osteoblatic niche and permeate to the vascular niche where intravasation of the cells through the sinusoidal system takes place. As in solid tumor metastasis, trans-vascular migration occurs and abut into extravasation and the involvement of a new site [35] or into the formation of a plasmacytoma.


  Therapeutic Implications Top


Over the last decade, many novel treatments have been developed. Many of these new treatments target both MM PCs as well as the BM microenvironment. New potential therapeutic targets include histone deacetylation, the catalytic activity of proteasomes, signaling pathways of Akt, mammalian target of rapamycin, MEK, as well as cellular expression of CS-1, CD38, and CD40.[79] Current gold standard treatments for MM include immunomodulators imide drug (IMiDs) namely targeting the tumor microenvironment and protosome inhibitors and melphalan primarily targeting tumor cells.

Historically, it was the investigation of thalidomide anti-angiogenic properties that led to the rapid expansion of novel clinical drugs.[80] Thalidomide is an IMiDs,[81] that not only demonstrates anti-angiogenic activity, but also enhances T cell- and NK cell-mediated immunological responses, apoptosis, and downregulates cytokine production within the BM microenvironment.[82],[83] Lenalidomide, a 4-amino-glutamyl analog of thalidomide that lacks the neurologic side effects of sedation and neuropathy with similar properties to thalidomide exerts an antitumor necrosis factor alpha activity, modulates the immune response stimulating activities of T cells and NK cells, induces apoptosis of tumor cells, and decreases the binding of MM cells to BMSCs.[83],[84],[85] In addition, IMiDs affect bone resorption by inhibiting OC formation.[86],[87] Newer studies demonstrate its effects on signal transduction that can partly explain its selective efficacy in subsets of myelodysplastic syndrome.[88] Lenalidomide, therefore interplay with the MM BM microenvironment.

Bortezomib is a proteasome inhibitor which can also cause ECs apoptosis.[88],[89] It has also been shown to inhibit VEGF, IL-6, Ang-1, Ang-2, and IGF-1 secretion in BMSCs and ECs.[90],[91] Bortezomib may also induce the differentiation of MSCs into osteoblasts and induce apoptosis of OCs.[92]

Interestingly, lenalidomide has been shown to sensitize MM PCs to other agents like bortezomib.[93] This perhaps explains why combination novel agents are more effective than single agent treatments.[94]

Bisphosphonates are a supportive medication commonly administered clinically in a patient with MM. Bisphosphonates have shown promise in reducing the risk of skeletal-related events.[95] Some studies have shown bisphosphonates inhibit OC activity and exert an anti-angiogenic activity. Bisphosphonate effect on the BM microenvironment has been shown to inhibit in vitro proliferation, chemotaxis, and angiogenesis of MM ECs.[96]

In our center, a treatment algorithm stratifies MM patients into transplant-eligible and noneligible patients. Transplant-eligible ones would receive a bortezomib-based induction therapy followed by high-dose chemotherapy and autologous stem cell transplantation, followed by consolidation and maintenance with lenalidomide. Transplant-ineligible patients would receive a bortezomib-based or lenalidomide-based therapy for an extended duration. Bisphosphonates are offered to all patients.

Although these novel agents target the PCs, stromal cells, and the microenvironment, they cannot completely eradicate the malignant clone, and their use aims at inducing long-lasting remissions rather that a complete cure. A better understanding of the pathophysiology of the disease may result in the discovery of novel targets and individualizing therapy with a potential for cure.


  Conclusions Top


MM remains an incurable disease with a fascinating pathophysiology. The interactions between tumor cells and their microenvironment have allowed for many novel approaches to treatment that induce long-term tumor quiescence with little cross-resistance. The maladaptive nature of MM PCs and the BM niche has been recognized to play a crucial role in the pathogenesis and progression of MM. The current standard of care and most active anti-MM agents, bortezomib, thalidomide, and lenalidomide, work against both the diseased cell and it microenvironment. Only by inhibiting the ever expanding targets of the disease PC and the microenvironment will we be able to eradicate this currently incurable blood cancer.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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