Introduction
Diabetes mellitus (DM) is a widely prevalent chronic health condition affecting approximately 463 million people (9.3%) worldwide, with type 2 contributing about 90% of the total cases [ 1 ]. Multiple myeloma (MM) is a plasma cell neoplasm that accounts for approximately 10% of all hematological malignancies [ 2 ]. Several studies suggest there is an increased incidence of cancer, mainly of the pancreas, liver, endometrium, breast, colorectum, bladder, and hematologic malignancies in individuals with type 2 DM [ 3 , 4 ]. The prevalence of DM in a retrospective study of 5383 MM patients was 15% (White, 12% and Black, 25%) [ 5 ]. Given the frequent co-occurrence of type 2 DM among MM patients, several studies have attempted to elucidate the potential link between these conditions [ 6 , 7 ]. This review summarizes the associations between DM and MM risk and outcomes, the impact of long-standing DM on the different clinical manifestations of MM, the various challenges faced by physicians in managing patients with coexistent DM and MM, and delves into the proposed mechanisms by which DM is postulated to increase cancer risk, especially MM risk.
Diabetes mellitus and time-dependent risk of MM
The relationship between DM and the time-dependent risk of MM was extensively examined in several studies, as seen in Table 1 and the impact of DM on MM outcomes and mortality is presented in Table 2 [ 4 – 13 ].
Table 1
DM as a risk factor for MM incidence.
DM Diabetes Mellitus, MM Multiple Myeloma, T1DM Type 1 Diabetes Mellitus, T2DM Type 2 Diabetes Mellitus, SIR Standardized Incidence Ratio, RR Relative Risk, OR Odds Ratio, HR Hazard Ratio, OAA Oral Antidiabetic Agents, NHL Non-Hodgkin Lymphoma, VA Veterans Affairs, CI Confidence Interval.
| Study Cohort/Location | Study Design | Total Number ( N ) | Outcome | Risk | 95% CI | Ref. |
| Registrants of a national diabetes registry (National Diabetes Services Scheme/NDSS), Australia | Retrospective study Follow up: 1997–2008 | Total = 953,382 T1DM = 80,676 T2DM = 872,706 | T1DM | SIR = 0.99 | 0.62–1.56 | Harding et al. [ 12 ] |
| Male | SIR = 1.37 | 0.84–2.24 | ||||
| Female | SIR = 0.30 | 0.08–1.21 | ||||
| T2DM | SIR = 1.19 | 1.12–1.27 | ||||
| Male | SIR = 1.13 | 1.04–1.22 | ||||
| Female | SIR = 1.31 | 1.19–1.44 | ||||
| Healthcare database from Ontario, Canada | Retrospective study Follow up: 1996–2015 | Total = 3,009,828 Patients with Diabetes = 1,003,276 Patients without Diabetes = 2,006,552 | Overall incidence | RR = 1.15 | 1.09–1.20 | Gong et al. [ 13 ] |
| Male | RR = 1.05 | 0.98–1.12 | ||||
| Female | RR = 1.17 | 1.08–1.26 | ||||
| Age < 65 | RR = 1.09 | 1.02–1.17 | ||||
| Age > 65 | RR = 1.05 | 0.98–1.12 | ||||
| Population-based study, Italy | Multicenter case-control study Follow up: 1990–1993 | Total = 4387 Cases = 2669 MM cases = 263 Controls = 1718 | OR = 0.70 | 0.40 −1.10 | Vineis et al. [ 8 ] | |
| 4 centers in Spain | Multicenter case-control study Follow up: 1998–2002 | Total = 1166 Cases = 565 Controls = 601 | DM treated without drugs | OR = 2.68 | 1.32–5.43 | Fortuny et al. [ 9 ] |
| DM treated with insulin | OR = 0.76 | 0.16−3.64 | ||||
| DM treated with OAA | OR = 1.52 | 0.47–4.92 | ||||
| European Prospective Investigation into Cancer and Nutrition (EPIC), 23 centers in 10 European countries | Multicenter prospective study Follow up: 1992–2000 | Total = 393,477 NHL and MM cases = 1213 | Overall | HR = 1.09 | 0.8–1.47 | Khan et al. [ 7 ] |
| Male | HR = 1.28 | 0.89–1.24 | ||||
| Female | HR = 0.71 | 0.41–1.24 | ||||
| Across 142 Veterans Affairs (VA) hospitals USA | Multicenter prospective study Follow up: 1969-1996 | Total men = 4,501,578 Black = 832,334 White = 3,669,244 | Overall | RR = 0.98 | 0.91–1.07 | Atchinson et al. [ 11 ] |
| White | RR = 1.02 | 0.92–1.13 | ||||
| Black | RR = 0.92 | 0.81–1.06 | ||||
| Asia, Europe and USA | Meta-analysis of 10 studies Follow up: 1982-2010 | Cohort Studies Total = 5,187,778 Cases = 6477 Case-Control Studies Cases = 3536 Controls = 26,604 | Overall | OR = 1.22 | 0.98–1.53 | Castillo et al. [ 6 ] |
| Cohort | OR = 1.17 | 0.92−1.50 | ||||
| Case-Control | OR = 1.41 | 0.69–2.89 | ||||
| Male | OR = 1.00 | 0.89–1.12 | ||||
| Female | OR = 1.24 | 0.79–1.92 | ||||
| Clalit Health Services (largest health maintenance organization), Israel | Retrospective study Follow up: 2002–2012 | Prevalent DM = 159,104 MM cases = 331 Men=74,756 Women=84,348 | Men | HR = 1.80 | 1.52–2.14 | Dankner et al. [ 4 ] |
| Women | HR = 1.58 | 1.30–1.92 | ||||
| Incident DM = 408,243 MM cases = 1016 Male = 193,835 Female = 214,408 | Men | <1 yr: HR = 6.72 | 5.75–7.86 | |||
| 1– < 2 yrs: HR = 1.94 | 1.40–2.70 | |||||
| 2–11 yrs: HR = 1.71 | 1.41–2.07 | |||||
| Women | <1 yr: HR = 7.13 | 6.01–8.44 | ||||
| 1– < 2 yrs: HR = 2.23 | 1.57–3.16 | |||||
| 2–11 yrs: HR = 1.69 | 1.36–2.09 |
Table 2
DM as a risk factor for MM mortality.
DM Diabetes Mellitus, MM Multiple Myeloma, T1DM Type 1 Diabetes Mellitus, T2DM Type 2 Diabetes Mellitus, SMR Standardized Mortality Ratio, HR Hazard Ratio, RR Relative Risk, CI Confidence Interval, MSKCC Memorial Sloan Kettering Cancer Center.
| Study Cohort/Location | Study Design | N | Outcome | Risk | 95% CI | Ref. |
| Employees of 84 companies/organizations in Chicago area (Chicago Heart Association Detection Project in Industry) | Multicenter prospective study Follow up: 1967–1973 | Total = 35,420 Male = 20,314 Female = 15,106 | Plasma glucose level (mg/dL) | Multivariable-adjusted HRs for multiple myeloma mortality, model 1 | Chiu et al. [ 10 ] | |
| Male | ||||||
| < 119 | HR = 1.00 | 1.00 | ||||
| 120–159 | HR = 1.42 | 0.70–2.88 | ||||
| 160–199 | HR = 0.42 | 0.12–1.51 | ||||
| ≥ 200 | HR = 0.54 | 0.12–2.46 | ||||
| Female | ||||||
| < 119 | HR = 1.00 | 1.00 | ||||
| 120–159 | HR = 0.94 | 0.36–2.42 | ||||
| 160–199 | HR = 0.94 | 0.28–3.12 | ||||
| ≥ 200 | HR = 3.06 | 1.05–8.93 | ||||
| Registrants of a national diabetes registry (National Diabetes Services Scheme/NDSS), Australia | Retrospective study Follow up: 1997–2008 | Total=953,382 T1DM = 80,676 T2DM = 872,706 | T1DM | SMR = 0.76 | 0.32–1.83 | Harding et al. [ 12 ] |
| Male | SMR = 1.17 | 0.49–2.82 | ||||
| Female | SMR = 0.00 | 0.00–0.00 | ||||
| T2DM | SMR = 0.95 | 0.87–1.04 | ||||
| Male | SMR = 0.94 | 0.83–1.05 | ||||
| Female | SMR = 1.03 | 0.87–1.20 | ||||
| Healthcare database from Ontario, Canada | Retrospective study Follow up: 1996-2015 | Total = 3,009,828 Patients with DM = 1,003,276 Patients without DM = 2,006,552 | Overall cancer-specific mortality | RR = 1.29 | 1.15–1.44 | Gong et al. [ 13 ] |
| Male | RR = 1.32 | 1.14–1.53 | ||||
| Female | RR = 1.24 | 1.03–1.50 | ||||
| Age < 65 | RR = 1.40 | 1.17–1.67 | ||||
| Age > 65 | RR = 1.23 | 1.06–1.43 | ||||
| MSKCC and Icahn School of Medicine at Mount Sinai, NY, USA | Retrospective study | Total = 5383 DM = 790 Without DM = 5383 Black = 1001 White = 4382 | Overall | HR = 1.27 | 1.11–1.47 | Shah et al. 2024 [ 14 ] |
| Black | HR = 1.08 | 0.81–1.44 | ||||
| White | HR = 1.35 | 1.15–1.59 |
Notably, a comprehensive population-based study conducted in Israel [ 4 ] involving 408,243 persons with incident diabetes highlighted an increased risk of overall cancer including MM (1016 MM cases) following a DM diagnosis, with the highest risk observed within the first year after DM diagnosis [hazard ratio (HR) for MM 7.13; 95% confidence interval (95%CI) 6.01–8.44 in women and HR 6.72; 95%CI 5.75–7.86 in men], gradually decreasing but persisting for 11 years [ 4 ]. Similarly, a Canadian study analyzing 3,009,828 individuals reported a significantly higher risk of hematologic malignancies, particularly MM, in individuals with DM (adjusted HR 1.15; 95% CI 1.09–1.20), with the strongest associations observed among women and those aged under 65 [ 13 ].
Furthermore, a large population-based matched case-control study in Sweden assessed the risk of nine lymphoproliferative disorders as well as unspecified amyloidosis after a DM diagnosis in about 94,579 cases. The study found an initial increase in lymphoproliferative disorders within the first six months. More than six months post-diagnosis, DM remained associated with an elevated risk of specific malignancies, including acute lymphoblastic leukemia (ALL), chronic lymphoblastic leukemia (CLL), monoclonal gammopathy of undetermined significance (MGUS) (OR 1.33; 95%CI 1.25–1.41), and amyloidosis (OR: 1.62; 95% CI 1.44–1.83) [ 14 ]. However, sensitivity analysis controlling for the number of clinic visits demonstrated that risk for MGUS was not increased after DM diagnosis (OR 0.99; 95% CI 0.92–1.07), suggesting that the previously observed associations could be due to a detection bias [ 14 ]. This phenomenon reflects a time-dependent risk, which is the elevated incidence of MM shortly after DM diagnosis, which may be due to overlapping symptoms or increased medical surveillance leading to earlier detection, rather than a true causal relationship. As discussed in the study, this risk tends to decrease over time, especially with better DM control although still present.
Recent data also support an association between type 2 DM and MGUS. A large population-based study from Taiwan evaluated over 3.1 million individuals with incident type 2 DM and reported a significantly increased risk of developing MGUS (adjusted HR 2.33, 95% CI 1.93–2.81) [ 15 ]. The study proposed that metabolic dysfunction, chronic inflammation, and insulin resistance may contribute to this association, although age at DM onset appeared to modify the risk. Complementing these epidemiologic findings, emerging interventional data suggest that targeting metabolic pathways may influence MGUS biology. A recent phase II study evaluating metformin in patients with low-risk MGUS reported favorable progression-free outcomes, supporting a potential role for metabolic and inflammatory modulation in early plasma cell disorders [ 16 ].
However, in other studies, while there is a consistent trend in the same direction, this link was not statistically significant. The European Prospective Investigation into Cancer and Nutrition (EPIC) cohort study, involving 393,477 participants, did not find a significantly increased risk of MM [1,213 non-Hodgkin’s lymphoma and MM cases] among patients with self-reported DM (HR 1.09; 95% CI 0.80–1.47) [ 7 ]. Similarly, a meta-analysis of 10 observational studies done among patients with MM found no significant association between type 2 DM and MM incidence (OR 1.22; 95% CI 0.98–1.53) [ 6 ]. A systematic review and meta-analysis including 13 articles initially found a higher risk of MM among type 2 DM patients (OR: 1.60; 95% CI 1.13–2.26), but after accounting for heterogeneity and excluding 2 studies with high heterogeneity, the final analysis demonstrated no significant association between type 2 DM and incidence of MM (OR: 1.05; 95% CI 0.83–1.33) [ 17 ].
While interpreting these results, it is possible that these associations are influenced by co-existing obesity in DM patients. Individuals with an elevated BMI are significantly more likely to have DM suggesting that obesity is one of the strongest risk factors for DM [ 18 ]. There is also robust data to support an association between obesity and risk for MGUS, transformation of MGUS to MM, risk for development of MM, and increased MM mortality [ 19 , 20 ] and in fact, obesity has been identified as a major modifiable risk factor for MM [ 21 ]. Thus, obesity may represent a major confounding factor in evaluating the relationship between DM and MM. However, analyses in most of the studies described above were adjusted for BMI [ 6 , 8 , 11 , 12 ].
Thus, overall, while some studies suggest that pre-diagnosis DM increases the risk for MM in a time-dependent manner, with the greatest risk immediately after DM diagnosis others suggest this risk is not present.
Effect of DM on MM outcomes and mortality
A screening study of 35,420 men and women (66 MM deaths) identified a statistically significant 3-fold higher risk of MM mortality among women with the highest level (> 200 mg/dL) of post-load glucose, defined as blood glucose measured one hour after administration of 50 g oral glucose load to nondiabetic participants without regard to fasting status, (multivariable adjusted HR: 3.06, 95% CI 1.05–8.93) [ 10 ]. Another study evaluating cancer risk and mortality among patients with type 1 and type 2 DM enrolled in a national diabetes registry in Australia revealed significantly elevated standardized mortality ratios (SMRs) for all cancers in type 1 diabetic males (SMR: 1.19; 95% CI: 1.07–1.33) and females (SMR: 1.32; 95% CI: 1.17–1.49), as well as in type 2 diabetic males (SMR: 1.03; 95% CI: 1.01–1.04) and females (SMR: 1.13; 95% CI: 1.11–1.15) [ 12 ]. However, for multiple myeloma specifically, SMRs were not significantly elevated—type 1 diabetic males had an SMR of 1.17 (95% CI: 0.49–2.82), no MM deaths were reported in type 1 diabetic females, while type 2 diabetic males and females had SMRs of 0.94 (95% CI: 0.83–1.05) and 1.03 (95% CI: 0.87–1.20) respectively [ 12 ]. A single-center study involving 310 patients newly diagnosed with MM between 1999 and 2007 in Taiwan demonstrated that MM patients with pre-existing DM had a significantly higher proportion of renal impairment (serum creatinine ≥ 2 mg/dL), International Staging System (ISS) stage III disease and all-cause mortality; lower rates of reversal of renal impairment and lower overall survival (OS) (11.7 vs. 22.4 months; HR 1.5; 95% CI 1.02–2.23) when compared to non-diabetic MM patients [ 22 ].
Another study of 1,083 MM patients revealed that diabetic (history of type 2 DM or steroid-induced diabetes) patients had a statistically significant decreased probability of achieving complete remission after induction therapy and reduced survival (median OS: 65.4 vs. 98.7 months) compared with non-diabetic patients [ 23 ]. In a retrospective analysis of 5383 MM patients from two US academic institutions (15% with DM), patients with DM had a reduced overall survival (HR 1.27; 95% CI 1.11, 1.47; P < 0.001), especially among white patients [ 5 ]. These findings emphasize the importance of DM management in improving MM survival.
In contrast, a small study evaluating the impact of comorbidities such as DM on median PFS and OS in 114 nondiabetics and 13 diabetics found no significant difference on univariate analysis [ 24 ].
This data suggests that DM negatively impacts MM survival as well as increases complications such as renal disease. These findings highlight the importance of clinicians emphasizing adequate glycemic control through medications or dietary modifications.
DM and MM involve various organ systems
Additionally, although the association between DM and MM risk differs by study, DM is associated with multiple complications that increase morbidity and mortality and may overlap with those observed in MM. Some of the major organ systems affected by DM include neurologic, cardiovascular, renal, and ophthalmic, all of which can also be involved in MM.
Neuropathy
Peripheral neuropathy (PN) has been associated with plasma cell disorders [ 25 ] and is also a common complication seen in DM [ 26 ]. Additionally, therapies like bortezomib and thalidomide used in MM are associated with PN [ 27 ]. There is some evidence to suggest that patients with a history of DM have a higher risk of bortezomib neurotoxicity [ 28 , 29 ]. However, the phase III APEX trial, randomizing patients with relapsed MM to bortezomib vs high-dose dexamethasone, showed that the incidence and severity of PN appeared to be unaffected by baseline glycosylated hemoglobin level or diabetes history [ 30 ]. PN can lead to various complications, such as falls and fractures, and reduce the quality of life in patients [ 31 , 32 ]. It is, therefore, essential to assess patients for PN before starting chemotherapy and closely monitor their symptoms after initiating therapy.
Nephropathy
Renal failure is a significant adverse prognostic factor in patients with plasma cell dyscrasias [ 33 ]. Monoclonal gammopathy of renal significance (MGRS) is known to cause glomerular diseases and tubulopathies, and can involve the vasculature with varying presentations in patients [ 34 ]. Renal insufficiency has been identified at initial diagnosis in 15–50% of MM patients [ 35 ]. A study revealed that patients with renal failure had a lower response rate to chemotherapy than those with normal renal function (39% vs. 56%; p < 0.01). This difference may be partly attributed to dose adjustments necessitated by renal dysfunction. Moreover, patients who experienced recovery of renal function had a prolonged median survival than those without (28 months vs. 4 months; p < 0.001) [ 36 ]. Notably, MM patients who experience recovery of renal function continue to have inferior outcomes compared with those with normal renal function at diagnosis. In a large study ( N = 1135 newly diagnosed MM patients), those who presented with creatinine clearance (CrCl) < 40 mL/min at diagnosis and remained <40 mL/min and those with CrCl < 40 mL/min at diagnosis but subsequently improved to ≥ 40 mL/min had markedly shorter median overall survival (33 and 56 months respectively) compared with patients who had normal renal function at diagnosis (112 months) ( p < 0.001), highlighting that reversal of renal impairment does not fully mitigate its adverse prognostic impact [ 37 ]. Diabetic nephropathy occurs in 20–40% of all diabetics [ 38 ]. DM was the strongest independent factor that worsened renal prognosis in patients aged ≥ 65 years with monoclonal immunoglobulin deposition diseases, including MM (HR 3.65; 95% CI 2.08–6.41) [ 33 ].
Ophthalmic Complications
Although rare, ophthalmic manifestations of MM are diverse, ranging from proptosis, diplopia, scleritis, episcleritis, secondary glaucoma, uveal plasmacytoma, hyperviscosity leading to retinal vessel dilation, retinopathy, macular detachment, and macular edema [ 39 ]. DM-induced retinopathy may further add to the ophthalmic side effects of MM therapy, such as cataracts from prolonged steroid use [ 40 , 41 ] and keratopathy from belantamab mafodotin, an antibody-drug conjugate targeting B-cell maturation antigen, which has been associated with corneal epithelial damage through its cytotoxic payload, leading to microcyst-like epithelial changes [ 42 ]. Additionally, bortezomib has been associated with ocular toxicities such as blurred vision, chalazion, conjunctivitis, and, in rare cases, reversible optic neuropathy, likely due to mitochondrial dysfunction in retinal ganglion cells [ 43 ].
Cardiovascular Disease
DM is a well-known risk factor for cardiovascular disease. Individuals with DM, particularly type 2 DM, have higher cardiovascular morbidity and mortality compared with non-diabetic subjects [ 44 , 45 ]. Vascular complications of type 1 and type 2 DM., are major contributors to the development of coronary artery disease (CAD), stroke, and heart failure in affected individuals [ 46 ]. Severe anemia in MM can also worsen cardiac complication risk. AL amyloidosis can directly lead to cardiac complications such as heart failure and cardiomyopathy. AL amyloidosis can have cardiac involvement in about 70–80% of cases [ 47 ]. Several agents used in the treatment of MM, such as anthracyclines and proteasome inhibitors like carfilzomib, have been associated with cardiotoxicity [ 48 ]. Prolonged use of steroids is associated with the development of DM and hypertension, both of which are major risk factors for cardiovascular disease. Therefore, DM coexistent with MM can worsen cardiovascular risk.
Immune system
Individuals with DM are known to have defects in both innate and adaptive immune responses which contribute to their increased risk for infections. Additionally, obesity is often seen concomitantly with DM and may further amplify this immune dysregulation and inflammation. Supporting this metabolic–immune link, Gaucher disease provides a clear example of how chronic inflammation, lysolipid accumulation, and insulin resistance can drive plasma-cell dysregulation. In Gaucher disease, the clonal immunoglobulin frequently targets lipid antigens such as lyso-glucosylceramide, and remarkably, about one-third of sporadic MGUS and MM cases also show reactivity to these lysolipids [ 49 ]. This suggests that persistent lipid-driven immune activation may contribute to early plasmacytic transformation. Given that type 2 DM and obesity also feature lysolipid abnormalities, NF-κB activation, and chronic inflammation, similar antigenic mechanisms may influence MGUS/MM development in these populations.
Additionally, suppression of cytokine production (IL-2, IL-6, IL-10, IL-12, IL-17A, IL-22, interferons etc), defective leukocyte recruitment (due to lower expression of cellular adhesion molecules and other cytokines), defective pathogen recognition (due to down regulation of toll-like receptors), neutrophil, macrophage, monocyte and NK cell dysfunction and inhibition of antibody and complement pathways has been described in various studies [ 50 – 52 ].
Immune dysregulation is the hallmark of MM as it primarily affects plasma cells critical for antibody production and interferes with the production of other essential immune cells such as T-cells and neutrophils [ 53 , 54 ]. As a result, infections are a leading cause of morbidity and mortality in MM patients. A Latin American cohort study identified DM (OR 2.71, 95% CI 1.23–6.00) as a significant risk factor for infection-related hospitalization and mortality in newly diagnosed MM patients [ 55 ].
In addition, MM therapies, including proteasome inhibitors (PIs), immunomodulatory drugs (IMiDs), and monoclonal antibodies (mAbs), significantly impact the immune system. PIs such as bortezomib can impair CD4 + T-cell function and have been associated with varicella-zoster virus reactivation [ 56 , 57 ]. CD38-directed monoclonal antibodies like daratumumab have been shown to reduce NK-cell counts, increasing infection risk [ 58 ]. In the context of immunotherapies, which rely heavily on intact immune surveillance, pre-existing immune dysfunction due to DM may further compromise efficacy and increase susceptibility to infections. There is data to suggest that diabetic patients with metastatic non-small cell lung cancer had a shorter PFS and OS when treated with pembrolizumab as compared to non-diabetic counterparts [ 59 ]. Similarly, as chimeric antigen receptor T-cell (CAR-T cell) therapy and bispecific antibodies emerge as the mainstay of treatment in relapsed, refractory multiple myeloma (RRMM) and possibly as part of upfront treatment for newly diagnosed multiple myeloma (NDMM) patients, the role of T-cell exhaustion as a mechanism of resistance to these therapies is being increasingly recognized [ 60 , 61 ]. Given the immune dysregulation occurring in DM patients, studies evaluating the impact of hyperglycemia and DM on outcomes of CAR-T cell and bispecific therapies are essential.
As such, individuals with DM may be at a disadvantage not only in mounting an adequate immune response to pathogens but also in recognizing and eliminating emerging tumor cells, which may contribute to MM pathogenesis and worsen outcomes in diabetic MM patients.
DM thus exacerbates MM complications across organ systems, including neurologic (PN), renal (nephropathy), ophthalmic, and cardiovascular manifestations, while also compromising immune function, potentially worsening MM outcomes.
Anti-hyperglycemic agents
Metformin use is associated with reduced overall cancer risk
Long-term use of metformin is associated with reduced incidence of cancer and cancer-related mortality [ 62 , 63 ]. A large meta-analysis of 265 studies (44 cohort studies and 39 case-control studies involving 7.6 million diabetic patients and 182 randomized controlled trials involving 137,540 diabetic patients) demonstrated reduced risk of cancer with metformin and thiazolidinediones (TZDs) (Relative Risk (RR) 0.86; 95%CI 0.83–0.90 and RR 0.93; 95% CI 0.91–0.96, respectively) [ 64 ]. The hypothesis that metformin synergizes with chemotherapeutic agents to increase chemosensitivity across a wide spectrum of malignancies has been evaluated in many case-control studies, meta-analyses, and is also currently being investigated prospectively in several clinical trials worldwide [ 62 ].
Metformin use is associated with reduced risk of transformation from MGUS to MM
Metformin use for ≥ 4 years was associated with a 53% lower risk of progression of MGUS to MM in a cohort of 2003 diabetic US veterans [ 65 ]. Based on this data, there is an ongoing clinical trial testing the effect of metformin on the prevention of progression in high-risk MGUS and low-risk SMM patients ( NCT04850846 ).
Anticancer mechanisms of metformin
Two widely accepted mechanisms are the inhibition of the AKT/mTOR signaling pathway with a consequent reduction in protein synthesis and suppression of cell proliferation [ 66 , 67 ] and reduction in circulating concentrations of insulin and insulin-like growth factor (IGF), thereby preventing activation of insulin and IGF receptor signaling pathways with resultant decreased growth promotion and mutagenesis [ 68 ]. Additionally, metformin has been shown to inhibit IL-6 receptor (IL-6R)–mediated signaling in MM cells through activation of AMPK, suppression of mTOR activity, and upregulation of the tumor-suppressor microRNA miR-34a, further supporting its potential antimyeloma effects [ 69 ]. Metformin was shown to suppress the induction of critical unfolded protein response effector glucose-regulated protein 78 (GRP78) with consequent impairment of autophagosome formation and enhancement of apoptosis when combined with bortezomib treatment in MM cell lines and patient tumor cells in-vitro [ 70 ]. These findings were also confirmed in-vivo in MM mice models in the same study.
Insulin increases cancer risk
In a study of 1303 Type 1 DM patients, insulin use was associated with increased cancer risk (incidence rate of 2.8 per 1000 person-years; 95%CI 2.2–3.3), especially with a higher insulin dose (HR 5.93; 95%CI 1.21–29.06), age (HR 1.08; 95%CI 1.05–1.12) and female sex (HR 1.74; 95%CI 1.15–2.64) [ 71 ].
Insulin may promote tumor growth both directly through insulin receptor activation and indirectly via upregulation of the insulin-like growth factor (IGF-1) signaling pathway [ 72 ]. Chronic hyperinsulinemia enhances hepatic production of IGF-1 and reduces IGF-1 binding proteins, thereby increasing bioavailability of IGF-1, which in turn activates IGF-1 receptors on malignant cells [ 73 ]. This axis is highly relevant to MM. IGF-1 has been shown to act as a potent myeloma growth factor at physiological concentrations [ 74 ]. Further supporting this, microarray analyses revealed significant overexpression of IGF-1 receptors in malignant plasma cells, indicating IGF’s signaling role in MM biology [ 75 ]. In a recent study, hyperinsulinemia was shown to accelerate MM progression as evidenced by increased tumor growth. In this study, MM.1S xenografts grew more rapidly in genetically engineered immunodeficient nonobese diabetic mice (Rag1−/−/MKR) compared to wild-type mice [ 5 ]. Western blot analysis revealed that these MM.1S xenografts from Rag1−/−/MKR mice had elevated levels of phosphorylated S6 ribosomal protein (Ser235/236) levels, indicating greater mTOR pathway activation [ 5 ]. This suggests a role for insulin signaling in promoting MM growth in vivo.
Additionally, a meta-regression analysis involving 21 case-control studies found that high circulating levels of IGF-1 are associated with increased cancer risk, including prostate (OR 1.49; 95% CI 1.14–1.95) and pre-menopausal breast cancer (OR 1.65, 95% CI 1.26–2.08), further highlighting the broad oncogenic potential of IGF signaling [ 76 ].
These findings collectively support the hypothesis that insulin and IGF-1 signaling may offer novel therapeutic strategies for MM prevention and treatment.
GLP-1 agonists are associated with reduced MM risk and reduced risk of transformation of MGUS to MM
Glucagon-like peptide 1 (GLP-1) agonists, recognized for their antidiabetic effects and cardiovascular benefits, have garnered attention for their potential role in slowing the progression of MGUS to MM in diabetic patients. Recent studies in US Veterans have shown a statistically significant 65% reduction in the risk of progression of MGUS to MM with GLP-1 agonist use (HR 0.35, 95% CI 0.14–0.90). Additionally, while GLP-1 agonist use demonstrated a remarkable 75% reduction in progression risk among white patients (HR 0.25; 95% CI 0.09–0.68), no significant decrease was observed in black patients (HR 1.01; 95% CI 0.36–2.90) [ 77 ]. In a large retrospective cohort study, GLP-1 agonist use was associated with a significantly lower incidence of MGUS (HR 0.68; 95% CI, 0.52–0.88) and MM (HR 0.49; 95% CI 0.31–0.76) compared to insulin use, whereas no significant difference was observed in incidence of MGUS (HR 1.23; 95%CI 0.93–1.63) or MM (HR 1.38; 95% CI 0.84–2.27) when compared to metformin use [ 78 ]. Similar findings were noted in another large nationwide retrospective cohort study of 1,651,452 US adults with type 2 DM, GLP-1 receptor agonist use was associated with a significantly lower risk of developing MM compared to insulin users (HR, 0.59; 95% CI, 0.44–0.77) [ 79 ]. These findings underscore the potential role of GLP-1 agonists in cancer prevention. Further prospective research trials are warranted to confirm these findings and further study underlying mechanisms.
Thus, metformin and GLP-1 agonists may potentially reduce the progression of MGUS to MM in diabetics via AKT/mTOR signaling modulation and impact on insulin/IGF pathway, while insulin use may be associated with an increased cancer risk. In addition to their metabolic effects, metformin and GLP-1 receptor agonists also improve the chronic inflammation and immune dysfunction seen in diabetes and obesity. Metformin reduces NF-κB activity and pro-inflammatory cytokines, while GLP-1 agonists have been shown to lower systemic inflammation and improve adipose-tissue inflammatory signaling [ 80 , 81 ]. These broader immunometabolic effects overlap with pathways involved in myeloma pathogenesis, raising the possibility that their favorable impact on MGUS and MM may in part relate to improving inflammation-driven immune dysregulation.
Pathways through which DM may cause carcinogenesis
Here, we outline the various mechanisms implicated in the increased cancer and MM risk associated with DM.
DM may contribute to carcinogenesis through three primary mechanisms: hormonal [insulin and insulin-like growth factor (IGF)], metabolic (hyperglycemia), and inflammatory [ 82 – 84 ] (Fig. 1 ). The association between the insulin/IGF axis and cancer progression has been extensively studied [ 76 ]. The association between insulin and cancer risk has been described above [ 71 ]. Hyperinsulinemia and insulin resistance in DM may also contribute to cancer development by activating the wingless-related integration site (Wnt) ligand, which either binds to an insulin receptor or increases circulating IGF levels [ 82 ]. Hyperinsulinemia also enhances hepatic IGF production [ 85 ] and exerts a pro-mitotic effect through insulin receptor-A (IR-A) [ 86 ]. MM cell lines have been shown to express IR-A and IGF receptors, which respond to IGFs by evading dexamethasone-induced apoptosis [ 87 ].

In addition to Wnt signaling, insulin and IGF also activate the phosphoinositide 3-kinase (PI3K)/AKT/ mTOR pathway- a central regulator of cell growth, proliferation, and survival [ 88 ]. Chronic activation of this pathway by hyperglycemia or increased IGF signaling contributes to carcinogenesis by promoting protein synthesis, inhibiting apoptosis, and enhancing glucose uptake in tumor cells [ 89 , 90 ]. Activation of PI3K /AKT signaling has been observed in MM, and this pathway may be further amplified in diabetic patients, providing a mechanistic link between metabolic dysregulation and plasma cell malignancy [ 91 , 92 ].
Hyperglycemia may increase carcinogenesis directly or indirectly. It can exert direct effects like the promotion of cell proliferation, inducing mutations, and influencing invasion, migration, and rewiring in cancer cells [ 83 ]. Indirectly, hyperglycemia may increase the circulation of insulin, IGF, and inflammatory cytokines, contributing to enhanced proliferation [ 83 ]. Interleukin-6 (IL-6), implicated in the development of various malignancies, including MM, is elevated in T2DM [ 93 , 94 ]. The pro-inflammatory state in uncontrolled DM, characterized by increased levels of IL-6, tumor necrosis factor-alpha (TNF-α), and C-reactive protein (CRP), along with increased monocyte activity and NF-κB activation, may contribute to carcinogenesis [ 95 ]. This chronic inflammation leads to oxidative stress that damages lipids, proteins, and DNA, contributing to carcinogenesis [ 96 ]. Furthermore, TNF-α activates the nuclear factor-kappa B (NF-κB) pathway, which promotes angiogenesis, metastasis, and proliferation of malignant cells while impairing adaptive immunity [ 97 , 98 ]. MM cells have exhibited mutations in the NF-κB pathway, suggesting a role in MM development [ 99 , 100 ].
DM can thus foster carcinogenesis through hormonal, metabolic, and inflammatory pathways, involving mechanisms such as hyperinsulinemia, hyperglycemia-driven cell proliferation, and chronic inflammation. The combined activation of insulin/IGF axis signaling and downstream activation of PI3K /AKT/ mTOR and NF-κB pathways provides a plausible link between diabetes and increased cancer risk, including MM development.
Dietary modifications for DM and MM
In addressing the complex interplay between DM and MM, lifestyle modifications, particularly dietary interventions, emerge as crucial considerations. Lifestyle and nutritional habits significantly contribute to the rising incidence of DM, emphasizing the importance of improved nutritional practices in preventing complications of DM [ 101 , 102 ]. Prior randomized dietary studies testing a whole food plant-based diet (low in fat and high in complex carbohydrates rich in fiber) for 16 weeks have shown an improvement in hemoglobin A1c, insulin resistance, and diabetes [ 103 , 104 ]. This is consistent with expert consensus statements published and may help clinicians counsel patients on their diet post-diagnosis [ 105 , 106 ]. These findings are consistent with the NUTRIVENTION trial that enrolled participants with MGUS and SMM with an elevated body mass index, and demonstrated that a high-fiber plant-based diet not only improved insulin resistance and adiponectin-leptin ratio (a marker of insulin resistance), but also reduced systemic inflammatory biomarkers such as C-reactive protein and increased anti-inflammatory classical monocytes. The intervention additionally increased gut microbiota alpha-diversity and abundance of butyrate-producing bacteria, supporting interconnected metabolic, inflammatory, and immune pathways relevant to both DM biology and early myeloma progression [ 107 ]. A participant on the trial with DM on insulin and GLP-1 agonist experienced weight loss but M spike continued to progress until he went on the high fiber dietary intervention when he was able to stop insulin, and M spike plateaued [ 107 ]. However, further prospective trials are needed to understand the role of diet in addressing insulin resistance and DM in plasma cell disorders. The NUTRIVENTION-3 in MGUS/SMM is recruiting ( NCT05640843 ). The NUTRIVENTION-4 trial ( NCT04497961 ) in MM survivors is completed ( NCT04497961 ) and the decentralized NUTRIVENTION-5 trial is testing a high fiber diet in newly diagnosed MM is recruiting ( NCT07226609 ).
Conclusion
The association and interactions between DM and cancer, including MM, highlights the need for continued research. Additionally, lifestyle factors, particularly diet, warrant attention in managing DM patients. This review highlights the existing evidence and emphasizes the need for multidisciplinary care to navigate the care of these patients.
Acknowledgements
Not applicable.
Author contributions
Richa Parikh and Ram Prakash Thirugnanasambandam contributed equally to the conceptualization, literature review, and initial drafting of the manuscript. Both also contributed equally to the revisions and worked together in submitting the final version. Urvi Shah provided senior oversight, guided the structure and focus of the review, and critically revised the manuscript for important intellectual content. All authors reviewed and approved the final version of the manuscript.
Funding
This study was funded by the Center for Hematologic Malignancies at MSK and in part through the NIH/NCI Cancer Center Support Grant P30 CA008748. [U.A.S.]. U.A.S. is supported by the American Society of Hematology Scholar Award, Paula and Rodger Riney Foundation, Willow Foundation, HealthTree Foundation, Gabrielle’s Angel Foundation and Blood Cancer United.
Data availability
No data is available for this article as it is a review article.
Competing interests
R. Parikh reports no conflicts of interest. R.P. Thirugnanasambandam reports no conflict of interest. U.A. Shah reports research funding support from BMS and Janssen, to the institution, non-financial research support from Sabinsa Pharmaceuticals and M and M Labs to the institution; personal fees/honorarium from Janssen Biotech, and Sanofi, outside the submitted work.
Ethical approval
The study did not require IRB approval as it is a review article.
Footnotes
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
These authors contributed equally: R Parikh, RP Thirugnanasambandam.
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Associated Data
Data Availability Statement
No data is available for this article as it is a review article.