Organoid Modeling of the Tumor Immune Microenvironment.

In vitro cancer cultures, including three-dimensional organoids, typically contain exclusively neoplastic epithelium but require artificial reconstitution to recapitulate the tumor microenvironment (TME). The co-culture of primary tumor epithelia with endogenous, syngeneic tumor-infiltrating lymphocytes (TILs) as a cohesive unit has been particularly elusive. Here, an air-liquid interface (ALI) method propagated patient-derived organoids (PDOs) from >100 human biopsies or mouse tumors in syngeneic immunocompetent hosts as tumor epithelia with native embedded immune cells (T, B, NK, macrophages). Robust droplet-based, single-cell simultaneous determination of gene expression and immune repertoire indicated that PDO TILs accurately preserved the original tumor T cell receptor (TCR) spectrum. Crucially, human and murine PDOs successfully modeled immune checkpoint blockade (ICB) with anti-PD-1- and/or anti-PD-L1 expanding and activating tumor antigen-specific TILs and eliciting tumor cytotoxicity. Organoid-based propagation of primary tumor epithelium en bloc with endogenous immune stroma should enable immuno-oncology investigations within the TME and facilitate personalized immunotherapy testing.

Relevance of BEST-CLI trial endpoints in a tertiary care limb preservation program.

OBJECTIVE: Major adverse limb event-free survival (MALE-FS) differed significantly by initial revascularization approach in the BEST-CLI randomized trial. The BEST-CLI trial represented a highly selected subgroup of patients seen in clinical practice; thus, we examined the endpoint of MALE-FS in an all-comers tertiary care practice setting. METHODS: This is a single-center retrospective study of consecutive, unique patients who underwent technically successful infrainguinal revascularization for chronic limb-threatening ischemia (2011-2021). MALE was major amputation (transtibial or above) or major reintervention (new bypass, open bypass revision, thrombectomy, or thrombolysis). RESULTS: Among 469 subjects, the mean age was 70 years, and 34% were female. Characteristics included diabetes (68%), end-stage renal disease (ESRD) (16%), Wound, Ischemia, and foot Infection (WIfI) stage 4 (44%), Global Limb Anatomic Staging System (GLASS) stage 3 (62%), and high pedal artery calcium score (pMAC) (22%). Index revascularization was autogenous vein bypass (AVB) (30%), non-autogenous bypass (NAB) (13%), or endovascular (ENDO) (57%). The composite endpoint of MALE or death occurred in 237 patients (51%) at a median time of 189 days from index revascularization. In an adjusted Cox model, factors independently associated with MALE or death included younger age, ESRD, WIfI stage 4, higher GLASS stage, and moderate-severe pMAC, whereas AVB was associated with improved MALE-FS. Freedom from MALE-FS, MALE, and major amputation at 30 days were 90%, 92%, and 95%; and at 1 year were 63%, 70%, and 83%, respectively. MALE occurred in 144 patients (31%) and was associated with ESRD, WIfI stage, GLASS stage, pMAC score, and index revascularization approach. AVB had superior durability, with adjusted 2-year freedom from MALE of 72%, compared with 66% for ENDO and 51% for NAB. Within the AVB group, spliced vein conduit had higher MALE compared with single-segment vein (hazard ratio, 1.8; 95% confidence interval, 0.9-3.7; P = .008 after inverse propensity weighting), but there was no statistically significant difference in major amputation. Of the 144 patients with any MALE, the first MALE was major reintervention in 47% and major amputation in 53%. Major amputation as first MALE was associated with non-AVB index approach. Indications for major reintervention were symptomatic stenosis/occlusion (54%), lack of clinical improvement (28%), asymptomatic graft stenosis (16%), and iatrogenic events (3%). Conversion to bypass occurred after 6% of ENDO cases, two-thirds of which involved distal bypass targets at the ankle or foot. CONCLUSIONS: In this consecutive, all-comers cohort, disease complexity was associated with procedural selection and MALE-FS. AVB independently provided the greatest MALE-FS and freedom from MALE and major amputation. Compared with the BEST-CLI randomized trial, MALE after ENDO in this series was more frequently major amputation, with relatively few conversions to open bypass.

Presenting limb severity is associated with long-term outcomes after infrainguinal revascularization for chronic limb-threatening ischemia.

OBJECTIVE: The SVS Wound, Ischemia, foot Infection (WIfI) limb staging system was established to estimate risk of major amputation in chronic limb-threatening ischemia (CLTI) and better stratify outcomes comparisons. There is little data on treatment outcomes beyond 1 year based on presenting WIfI stage. METHODS: This is a single-institution retrospective study of 413 patients who underwent infrainguinal revascularization for CLTI (2011-2021) with data available for WIfI staging. Patient characteristics and outcomes were gathered from the electronic medical record. Data were analyzed based on presenting WIfI stage and initial treatment received at our center. RESULTS: Presenting WIfI stages were 1 to 2 (23%), 3 (27%), and 4 (50%). Index revascularization approach was endoluminal (59%), autogenous vein bypass (29%), or non-autogenous bypass (13%). Operative mortality within 30 days was 2.9% and was not associated with WIfI stage or revascularization approach. Median limb follow-up time was 502 days (interquartile range [IQR], 112-1256 days), and median survival follow-up time was 932 days (IQR, 343-1770 days). Major amputation or death occurred in 19% and 46% of patients at median times of 119 days (IQR, 28-314 days) and 739 days (IQR, 204-1475 days), respectively. WIfI stage was independently associated with major amputation (P = .001), as was initial revascularization approach (P = .01). In a Cox proportional hazards model, factors independently associated with major amputation were male sex (hazard ratio [HR], 1.4; 95% confidence interval [CI], 1.04-2.0; P = .03), diabetes (HR, 1.8; 95% CI, 1.3-2.5; P = .001), WIfI stage 4 (HR, 2.3; 95% CI, 1.5-3.5; P < .001), and non-autogenous bypass (HR, 2.9; 95% CI, 2.1-4.2; P < .001). In a Cox proportional hazards model for mortality, independently associated factors were age (HR, 1.04; 95% CI, 1.02-1.05; P < .001), end-stage renal disease (HR, 2.8; 95% CI, 1.9-4.0; P < .001), congestive heart failure (HR, 1.9; 95% CI, 1.4-2.5; P < .001), chronic obstructive pulmonary disease (HR, 1.5; 95% CI, 1.1-2.1; P = .02), and WIfI stage 4 (HR, 1.6; 95% CI, 1.04-2.2; P = .03). Among those presenting with WIfI stage 4 limbs, Kaplan-Meier estimated rates of freedom from major amputation or death at 2 years were 71% ± 3.7% and 68% ± 3.5%, respectively. In an inverse propensity weighted Cox proportional hazards model, non-white race (HR, 1.5; 95% CI, 1.01-2.2; P = .047), diabetes (HR, 2.0; 95% CI, 1.2-3.3; P = .008), Global Anatomic Staging System infrapopliteal grade (HR, 1.2; 95% CI, 1.05-1.3; P = .005), non-autogenous bypass (HR, 3.2; 95% CI, 1.9-5.3; P < .001), and endoluminal revascularization (HR, 2.6; 95% CI, 1.6-4.3; P < .001) were independently associated with major amputation in the WIfI stage 4 subgroup. CONCLUSIONS: Presenting WIfI stage is strongly associated with long-term risks of major amputation and death following infrainguinal revascularization for CLTI and should be used to stratify outcomes comparisons. Effective revascularization is critical in WIfI stage 4 disease, and autogenous vein bypass provides durable long-term limb preservation.

Limb-based patency as a measure of effective revascularization for chronic limb-threatening ischemia.

OBJECTIVE: In 2019, the Global Vascular Guidelines on chronic limb-threatening ischemia (CLTI) introduced the concept of limb-based patency (LBP) defined as maintained patency of a target artery pathway after intervention. The purpose of this study was to investigate the relationship between LBP and major adverse limb events (MALE) after infrainguinal revascularization for CLTI. METHODS: Consecutive patients undergoing revascularization for CLTI between 2016 and 2019 at a single tertiary institution with a dedicated limb preservation team were included. Subjects with aortoiliac disease, prior infrainguinal stents, or existing bypass grafts were excluded. Demographics, Global Limb Anatomic Staging System scores, Wound, Ischemia, foot Infection (WIfI) stages, revascularization details, and limb-specific outcomes were reviewed. LBP was defined by the absence of reintervention, occlusion, critical stenosis (>70%), or hemodynamic compromise with ongoing symptoms of CLTI. MALE included thrombectomy or thrombolysis, new bypass, open surgical graft revision and/or major amputation. RESULTS: We analyzed 184 unique limbs in 163 patients. This cohort was composed of 66.9% male patients with a mean age of 72 years. Baseline characteristics included diabetes (66%), tissue loss (91%), and advanced WIfI stages (30% stage 3, 51% stage 4). Global Limb Anatomic Staging System stage 3 anatomic patterns were common (n = 119 [65%]). Sixty limbs were treated with open bypass (65% involving tibial targets) and 124 underwent endovascular intervention (70% including infrapopliteal targets). The 12-month freedom from MALE and loss of LBP were 74.0% ± 3.7% and 48.6% ± 4.2%, respectively. Diabetes (hazard ratio [HR], 2.56; 95% confidence interval [CI], 1.13-5.83; P = .025) and loss of LBP (HR, 4.12; 95% CI, 1.96-8.64; P < .001) were independent predictors of MALE in a Cox proportional hazard model. Loss of LBP was the sole independent predictor of major limb amputation after revascularization (HR, 4.97; 95% CI, 1.89-13.09; P = .001). Loss of LBP impacted both intermediate-risk limbs (HR, 2.85; 95% CI, 1.02-7.97; P = .047 in WIfI stages 1-3) and high-risk limbs (HR, 3.99; 95% CI, 1.32-12.11; P = .014 in WIfI stage 4). However, the loss of LBP had the greatest impact on patients presenting with WIfI stage 4 disease (31% vs 8% major limb amputation at 12 months in limbs without vs with maintained LBP). CONCLUSIONS: The anatomic durability of revascularization, as measured by LBP, is a key determinant of treatment outcomes in CLTI regardless of the initial mode of intervention undertaken. Loss of LBP is most detrimental in patients presenting with advanced limb threat (WIfI stage 4).

Capturing the complexity of open abdominal aortic surgery in the endovascular era.

OBJECTIVE: Volume and quality benchmarks for open abdominal aortic surgery and particularly open aortic aneurysm repair (OAR) in the endovascular era are guided by the Society for Vascular Surgery guidelines, but the Vascular Quality Initiative (VQI) OAR module fails to capture the full spectrum of complex OAR. We hypothesized that VQI-ineligible complex OAR would be the dominant form of open repairs performed at a VQI-participating tertiary center. METHODS: All OAR cases performed at a single tertiary care center from 2007 to 2020 were reviewed. The VQI OAR criteria were applied with exclusions (non-VQI) defined as concomitant renal bypass, clamping above the superior mesenteric artery or celiac artery, repairs performed for trauma, anastomotic aneurysm, isolated iliac aneurysm, or infected aneurysms. Linear regression was used to assess temporal trends. RESULTS: Among a total of 481 open abdominal aortic operations, 355 (74%) were OAR. The average annual OAR volume remained stable over 14 years (25 ± 6; P = .46). Non-VQI OAR comprised 54% of all cases and persisted over time (R2 = 0.047, P = .46). Supraceliac clamping (35%) was often necessary. The proportion of endograft explantation cases significantly increased over time from 4% in 2007 to 20% in 2019 (P = .01). Infectious indications represented 20% (n = 70) of cases. Visceral branch grafts were performed in 16% of all cases. OAR for ruptured aneurysm constituted 10% of cases. Thirty-day mortality was significantly higher in non-VQI vs VQI-eligible OAR cases (10% vs 4%; P = .04). CONCLUSIONS: Complex OAR comprises a majority of OAR cases in a contemporary tertiary referral hospital, yet these cases are not accounted for in the VQI. Creation of a "complex OAR" VQI module would capture these cases in a quality-driven national registry and help to better inform benchmarks for volume and outcomes in aortic surgery.

Pedal arterial calcification score is associated with the risk of major amputation in chronic limb-threatening ischemia.

OBJECTIVE: The medial arterial calcification (MAC) score is a simple metric that describes the burden of inframalleolar calcification using a plain foot radiograph. We hypothesized that a higher MAC score would be independently associated with the risk of major amputation in patients with chronic limb-threatening ischemia (CLTI). METHODS: We performed a single-institution, retrospective study of 250 patients who had undergone infrainguinal revascularization for CLTI from January 2011 to July 2019 and had foot radiographs available for MAC score calculation. A single blinded reviewer assigned MAC scores of 0 to 5 using two-view minimum plain foot radiographs, with 1 point each for calcification of >2 cm in the dorsalis pedis, plantar, and metatarsal arteries and >1 cm in the hallux and non-hallux digital arteries. RESULTS: The MAC score was 0 in 36%, 1 in 5.2%, 2 in 8.4%, 3 in 14%, 4 in 14%, and 5 in 21%. The MAC score was trichotomized to facilitate analysis and clinical utility (mild, MAC score 0-1; moderate, MAC score 2-4; and severe, MAC score 5). The variables independently associated with a higher MAC score were male sex, diabetes, end-stage renal disease, and the global limb anatomic staging system pedal score. The MAC score was not associated with the Society for Vascular Surgery WIfI (wound, ischemia, foot infection) grade or overall WIfI stage (P = .58). The median follow-up was 759 days (interquartile range, 264-1541 days). A higher MAC score was significantly associated with the risk of major amputation (P < .0001). In a Cox proportional hazards multiple regression model for major amputation that included the trichotomized MAC score, diabetes, end-stage renal disease, and WIfI stage (1-3 vs 4). The MAC score (MAC score 5: hazard ratio [HR], 4.9; 95% confidence interval [CI], 1.9-13.1; P = .001; MAC score 2-4: HR, 3.4; 95% CI, 1.3-8.8; P = .01) and WIfI stage (WIfI stage 4: HR, 2.1; 95% CI, 1.1-3.9; P = .03) were significantly associated with the risk of major amputation. In the subsets of patients with the most advanced WIfI stage of 3 to 4 (191 of 250; 76%) and patients with diabetes (185 of 250; 74%), the MAC score further stratified the risk of major amputation on univariate and multivariate analyses. CONCLUSIONS: The MAC score is a simple, practical tool and a strong independent predictor of major amputation in patients with CLTI. It provides novel clinical data that are currently unmeasured using any validated CLTI staging system. The MAC score is a promising standardized measure of inframalleolar disease burden that can be used in conjunction with the WIfI staging system to help improve outcomes stratification and determine the optimal treatment strategies for patients with CLTI.

Pedal arterial calcification score is associated with hemodynamic change and major amputation after infrainguinal revascularization for chronic limb-threatening ischemia.

OBJECTIVE: Pedal medial arterial calcification (pMAC) is associated with major amputation in patients with chronic limb-threatening ischemia (CLTI). We hypothesize that this association would be related to unresolved distal ischemia. We investigated relationships across pMAC score, hemodynamic change, and major amputation after infrainguinal revascularization for CLTI. METHODS: This is a single-institution, retrospective study of 306 patients who underwent technically successful infrainguinal revascularization for CLTI (2011-2020) and had foot x-rays for blinded pMAC scoring (0-5). A total of 136 (44%) patients had toe pressure measurements performed within 90 days before and 60 days after revascularization. Ischemia grade (0-3) was assigned using the Society for Vascular Surgery Wound, Ischemia, foot Infection (WIfI) system. RESULTS: The revascularization approach was open bypass in 118 (38%) and endovascular in 188 (62%) patients. pMAC scores were trichotomized (0-1 [125; 41%], 2-4 [116; 38%], 5 [65; 21%]). Post-revascularization WIfI ischemia grade was improved in 78 of 136 (57%) and unchanged/worsened in 58 of 136 (43%). A lower pMAC score was associated with hemodynamic improvement (P = .004). Failure to improve the ischemia grade was associated with major amputation (P = .0002). In the endovascular subgroup, WIfI ischemia grade was improved in 43 of 90 (48%) with available measurements, and 37 of 188 (20%) underwent major amputation. In a multivariate logistic model, pMAC 5 was the only factor independently associated with unimproved ischemia grade after endovascular treatment (odds ratio: 4.0 [1.1-16.6], P = .04). In a Cox proportional hazards model, factors independently associated with major amputation after endoluminal revascularization were WIfI stage 4 (hazard ratio [HR]: 2.7 [1.3-5.7], P = .007) and pMAC score (pMAC: 2-4: HR: 10.6 [1.4-80.7], P = .02; pMAC: 5: HR: 15.5 [2.0-119], P = .008). In the bypass subgroup, WIfI ischemia grade was improved in 35 of 46 (76%) with available measurements but was not associated with pMAC score (P = .88) or any other baseline patient or limb characteristics. A total of 19 of 118 (16%) patients underwent major amputation. In a Cox proportional hazards model including bypass conduit, WIfI stage, and pMAC score, the only factor independently associated with major amputation after bypass was use of nonautologous conduit (HR: 5.6 [1.8-17.6], P = .003). CONCLUSIONS: The pMAC score is independently associated with persistent distal ischemia and major amputation after technically successful revascularization for CLTI. These data suggest that pMAC may be a marker for hemodynamic response to revascularization and risk of limb loss, and it may have a stronger influence on the outcome of endoluminal interventions.

Long-term Lower Extremity and Cardiovascular Complications after Simultaneous Pancreas-Kidney Transplant.

Lower extremity (LE) vascular disease and adverse cardiovascular events (ACEs) cause significant long-term morbidity after simultaneous pancreas-kidney (SPK) transplantation. This study's purpose was to describe the incidence of, and risk factors associated with, LE vascular complications and related ACEs following SPK. All SPKs performed at the authors' institution from 2000 to 2019 were retrospectively analyzed. The primary outcome was any LE vascular event, defined as LE endovascular intervention, open surgery, amputation, or invasive podiatry intervention. Secondary outcomes included post-SPK ACE. A total of 363 patients were included, of whom 54 (14.9%) required at least one LE vascular intervention following SPK. Only 3 patients received pre-SPK ankle brachial indices (ABIs). A history of peripheral artery disease (PAD) (HR 2.95, CI 1.4-6.2) was a risk factor for post-SPK LE vascular intervention even after adjustment for other factors. Fifty-nine (16.3%) patients experienced an ACE in follow-up. Requiring a LE intervention post-SPK was associated with a subsequent ACE (HR 2.3, CI 1.2-4.5). LE vascular and cardiovascular complications continue to be significant sources of morbidity for SPK patients, especially for patients with preexisting PAD. The highest risk patients may benefit from more intensive pre- and post-SPK workup with ABIs and follow-up with a vascular surgeon.

Retransplantation After Living Donor Liver Transplantation: Data from the Adult to Adult Living Donor Liver Transplantation Study.

BACKGROUND: The use of living donor liver transplantation (LDLT) for primary liver transplantation (LT) may quell concerns about allocating deceased donor organs if the need for retransplantation (re-LT) arises because the primary LT did not draw from the limited organ pool. However, outcomes of re-LT after LDLT are poorly studied. The purpose of this study was to analyze the Adult to Adult Living Donor Liver Transplantation Study (A2ALL) data to report outcomes of re-LT after LDLT, with a focus on long-term survival after re-LT. METHODS: A retrospective review of A2ALL data collected between 1998 and 2014 was performed. Patients were excluded if they received a deceased donor LT. Demographic data, postoperative outcomes and complications, graft and patient survival, and predictors of re-LT and patient survival were assessed. RESULTS: Of the 1065 patients who underwent LDLT during the study time period, 110 recipients (10.3%) required re-LT. In multivariable analyses, hepatitis C virus, longer length of stay at LDLT, hepatic artery thrombosis, biliary stricture, infection, and disease recurrence were associated with an increased risk of re-LT. Patient survival among re-LT patients was significantly inferior to those who underwent primary transplant only at 1 (86% versus 92%), 5 (64% versus 82%), and 10 years (44% versus 68%). CONCLUSIONS: Approximately 10% of A2ALL patients who underwent primary LDLT required re-LT. Compared with patients who underwent primary LT, survival among re-LT recipients was worse at 1, 5, and 10 years after LT, and re-LT was associated with a significantly increased risk of death in multivariable modeling (hazard ratios, 2.29; P < 0.001).

Live Donor Liver Transplantation in the United States: Impact of Share 35 on Live Donor Utilization.

BACKGROUND: Share 35 was a policy implemented in 2013 to increase regional sharing of deceased donor livers to patients with model for end-stage liver disease ≥ 35 to decrease waitlist mortality for the sickest patients awaiting liver transplantation (LT). The purpose of this study was to determine whether live donor liver transplantation (LDLT) volume was impacted by the shift in allocation of deceased donor livers to patients with higher model for end-stage liver disease scores. METHODS: Using Network for Organ Sharing/Organ Procurement and Transplantation Network Standard Transplant Analysis and Research files, we identified all adults who received a primary LT between October 1, 2008, and March 31, 2018. LT from October 1, 2008, through June 30, 2013, was designated as the pre-Share 35 era and July 1, 2013, through March 31, 2018, as the post-Share 35 era. Primary outcomes included transplant volumes, graft survival, and patient survival in both eras. RESULTS: In total, 48 779 primary adult single-organ LT occurred during the study period (22 255 pre-Share 35, 26 524 post). LDLT increased significantly (6.8% post versus 5.7% pre, P < 0.001). LDLT volume varied significantly by region (P < 0.001) with regions 2, 4, 5, and 8 demonstrating significant increases in LDLT volume post-Share 35. The number of centers performing LDLT increased only in regions 4, 6, and 11. Throughout the 2 eras, there was no difference in graft or patient survival for LDLT recipients. CONCLUSIONS: Overall, LDLT volume increased following the implementation of Share 35, which was largely due to increased LDLT volume at centers with experience in LDLT, and corresponded to significant geographic variation in LDLT utilization.

Utility of a Simplified Iliac Artery Calcium Scoring System to Guide Perioperative Management for Renal Transplantation.

Non-contrast computed tomography scans of the abdomen and pelvis (CTAP) are often obtained prior to renal transplant to evaluate the iliac arteries and help guide surgical implantation. The purpose of this study was to describe the association of iliac calcification scores with operative and clinical outcomes using a simplified scoring system. A retrospective review of 204 patients who underwent renal transplant from 1/2013 to 11/2014 and who had a CTAP within 3 years prior to transplant was performed. Data were collected from the electronic medical record. Common iliac artery (CIA) and external iliac artery (EIA) calcification on CTAP were assessed using a simple scoring system. Descriptive statistics, logistic regression, and survival analyses were performed. A total of 204 patients were included in the analysis. The mean age was 57.4 ± 11.2 years and 134/204 (66%) were men. Nineteen patients (9%) had a history of peripheral artery disease (PAD), 78 (38%) had coronary artery disease, and 22 (11%) had a previous cerebrovascular accident (CVA). Patients with severe right EIA plaque morphology were significantly more likely to require arterial reconstruction compared to those without severe plaque (3/14[21%] 4/153 [3%], p = 0.03). Eleven patients (5%) had one or more amputations (toe, foot, or transtibial) following transplant. In UV logistic regression, severe EIA plaque morphology (OR 8.1, CI 2.2-29.6, p = 0.002) and PAD (OR 10.7, CI 2.8-39.9, p = 0.0004) were associated with increased odds of amputation. In the MV model containing both variables, EIA plaque morphology (OR 4.4, CI 0.99-18.3, p = 0.04) and PAD (OR 6.3, CI 1.4-26.4, p = 0.01) remained independently associated with increased odds of amputation. Over a median follow up of 3.3 years (IQR 2.9-3.6), 21 patients (10%) had post-operative major adverse cardiac events (MACE, defined as myocardial infarction, coronary intervention, or CVA), and 23 patients died (11%). In unadjusted Kaplan Meier analysis, CIA plaque (p = 0.00081) and >75% CIA length calcification (p = 0.0015) were significantly associated with MACE. Plaque burden in the EIA is associated with increased need for intra-operative arterial reconstruction and post-operative lower extremity amputations, while CIA plaque is associated with post-operative MACE. Assessment of CIA and EIA calcification scores on pre-transplant CT scans in high risk patients may guide operative strategy and perioperative management to improve clinical outcomes.

Biologics in gastrointestinal and pancreatic neuroendocrine tumors.

The development of biologic agents has ushered in a new era of precision medicine, opening the door to new therapeutic options designed to intelligently target cancer cells and their promoting factors, while leaving normal cells relatively unharmed. Biologics for the treatment of neuroendocrine tumors (NETs) have followed in the footsteps of regimens targeting pathways upregulated in other cancers, including the vascular endothelial growth factor (VEGF) and the mammalian target of rapamycin (mTOR). Through a number of clinical trials, the mTOR inhibitor everolimus and the receptor tyrosine kinase (RTK) inhibitor sunitinib were recently approved for NETs. Other biologics such as the VEGF-A inhibitor bevacizumab have also demonstrated promising clinical activity in NETs. Interestingly, though trials have demonstrated the efficacy of everolimus and sunitinib in extending progression-free survival (PFS) in NETs, objective response rates (RR) are uniformly low, indicating that the primary effect of these drugs is maintenance of stable disease. Due to the relatively indolent nature of the more common, well-differentiated variety of NETs, stable disease is often a reasonable goal for NET patients. Well-differentiated NETs have been shown to be poor responders to cytotoxic chemotherapy, underlining the important role of biologics in treating and managing NETs and their hormonal symptoms. Ongoing and future trials are investigating a wide variety of biologic compounds in NETs, including other RTK inhibitors, mTOR pathway inhibitors, and immune checkpoint inhibitors. Within this review, we will discuss major trials leading up to the FDA approval of everolimus and sunitinib for NETs, as well as other promising biologics currently under investigation in NET clinical trials.

DNA-repair defects in pancreatic neuroendocrine tumors and potential clinical applications.

BACKGROUND: The role of DNA repair in pathogenesis and response to treatment is not well understood in pancreatic neuroendocrine tumors (pNETs). However, the existing literature reveals important preliminary trends and targets in the genetic landscape of pNETs. Notably, pNETs have been shown to harbor defects in the direct reversal MGMT gene and the DNA mismatch repair genes, suggesting that these genes may be strong candidates for further prospective studies. METHODS: PubMed searches were conducted for original studies assessing the DNA repair genes MGMT and MMR in pNETs, as well as for PTEN and MEN1, which are not directly DNA repair genes but are involved in DNA repair pathways. Searches were specific to pNETs, yielding five original studies on MGMT and four on MMR. Six original papers studied PTEN in pNETs. Five studied MEN1 in pNETs, and two others implicated MEN1 in DNA repair processes. RESULTS: The five studies on MGMT in pNET tumor samples found MGMT loss of between 24% and 51% of tumor samples by IHC staining and between 0% and 40% by promoter hypermethylation, revealing discrepancies in methods assessing MGMT expression as well as potential weaknesses in the correlation between MGMT IHC expression and promoter hypermethylation rates. Four studies on MMR in pNET tumor samples indicated similar ambiguities, as promoter hypermethylation of the MLH1 MMR gene ranged from 0% to 31% of pNETs, while IHC staining revealed loss of MMR genes in between 0% and 36% of pNETs sampled. Studies also indicated that PTEN and MEN1 are commonly mutated or underexpressed genes in pNETs, although frequency of mutation or loss of expression was again variable among different studies. CONCLUSION: Further studies are essential in determining a more thorough repertoire of DNA repair defects in pNETs and the clinical significance of these defects. This literature review synthesises the existing knowledge of relevant DNA repair pathways and studies of the specific genes that carry out these repair mechanisms in pNETs.