New proposal to address mediation analysis interrogations by using genetic variants as instrumental variables.

The application of causal mediation analysis (CMA) considering the mediation effect of a third variable is increasing in epidemiological studies; however, this requires fitting strong assumptions on confounding bias. To address this limitation, we propose an extension of CMA combining it with Mendelian randomization (MRinCMA). We applied the new approach to analyse the causal effect of obesity and diabetes on pancreatic cancer, considering each factor as potential mediator. To check the performance of MRinCMA under several conditions/scenarios, we used it in different simulated data sets and compared it with structural equation models. For continuous variables, MRinCMA and structural equation models performed similarly, suggesting that both approaches are valid to obtain unbiased estimates. When noncontinuous variables were considered, MRinCMA presented, overall, lower bias than structural equation models. By applying MRinCMA, we did not find any evidence of causality of obesity or diabetes on pancreatic cancer. With this new methodology, researchers would be able to address CMA hypotheses by appropriately accounting for the confounding bias assumption regardless of the conditions used in their studies in different settings.

Avoiding collider bias in Mendelian randomization when performing stratified analyses.

Mendelian randomization (MR) uses genetic variants as instrumental variables to investigate the causal effect of a risk factor on an outcome. A collider is a variable influenced by two or more other variables. Naive calculation of MR estimates in strata of the population defined by a collider, such as a variable affected by the risk factor, can result in collider bias. We propose an approach that allows MR estimation in strata of the population while avoiding collider bias. This approach constructs a new variable, the residual collider, as the residual from regression of the collider on the genetic instrument, and then calculates causal estimates in strata defined by quantiles of the residual collider. Estimates stratified on the residual collider will typically have an equivalent interpretation to estimates stratified on the collider, but they are not subject to collider bias. We apply the approach in several simulation scenarios considering different characteristics of the collider variable and strengths of the instrument. We then apply the proposed approach to investigate the causal effect of smoking on bladder cancer in strata of the population defined by bodyweight. The new approach generated unbiased estimates in all the simulation settings. In the applied example, we observed a trend in the stratum-specific MR estimates at different bodyweight levels that suggested stronger effects of smoking on bladder cancer among individuals with lower bodyweight. The proposed approach can be used to perform MR studying heterogeneity among subgroups of the population while avoiding collider bias.

Deciphering the complex interplay between pancreatic cancer, diabetes mellitus subtypes and obesity/BMI through causal inference and mediation analyses.

OBJECTIVES: To characterise the association between type 2 diabetes mellitus (T2DM) subtypes (new-onset T2DM (NODM) or long-standing T2DM (LSDM)) and pancreatic cancer (PC) risk, to explore the direction of causation through Mendelian randomisation (MR) analysis and to assess the mediation role of body mass index (BMI). DESIGN: Information about T2DM and related factors was collected from 2018 PC cases and 1540 controls from the PanGenEU (European Study into Digestive Illnesses and Genetics) study. A subset of PC cases and controls had glycated haemoglobin, C-peptide and genotype data. Multivariate logistic regression models were applied to derive ORs and 95% CIs. T2DM and PC-related single nucleotide polymorphism (SNP) were used as instrumental variables (IVs) in bidirectional MR analysis to test for two-way causal associations between PC, NODM and LSDM. Indirect and direct effects of the BMI-T2DM-PC association were further explored using mediation analysis. RESULTS: T2DM was associated with an increased PC risk when compared with non-T2DM (OR=2.50; 95% CI: 2.05 to 3.05), the risk being greater for NODM (OR=6.39; 95% CI: 4.18 to 9.78) and insulin users (OR=3.69; 95% CI: 2.80 to 4.86). The causal association between T2DM (57-SNP IV) and PC was not statistically significant (ORLSDM=1.08, 95% CI: 0.86 to 1.29, ORNODM=1.06, 95% CI: 0.95 to 1.17). In contrast, there was a causal association between PC (40-SNP IV) and NODM (OR=2.85; 95% CI: 2.04 to 3.98), although genetic pleiotropy was present (MR-Egger: p value=0.03). Potential mediating effects of BMI (125-SNPs as IV), particularly in terms of weight loss, were evidenced on the NODM-PC association (indirect effect for BMI in previous years=0.55). CONCLUSION: Findings of this study do not support a causal effect of LSDM on PC, but suggest that PC causes NODM. The interplay between obesity, PC and T2DM is complex.

Follow-up care of 12 months of patients with bladder cancer in Spain: A multicenter prospective cohort study.

The therapeutic approach of bladder cancer strongly determines its prognosis. We describe the treatments and outcomes for a Spanish cohort of patients with bladder cancer for the first 12 months after diagnosis and identify the factors that influenced the decision to undergo the treatment received. We conducted a multicenter, prospective, cohort study including primary bladder cancer patients during the first 12 months after diagnosis. The clinical outcomes were performance status (ECOG), adverse events and any cause of mortality. We stratified the analysis by factors that might influence the treatments received. We conducted univariate and multivariable logistic regression models to assess which patient and tumor characteristics were associated with receiving adjuvant treatment in the subgroup of noninvasive bladder cancer patients. In total, 314 patients were included (85% men; 53.8% >70 years) in 7 tertiary Spanish hospitals; 82.2% had a noninvasive urothelial bladder cancer (NMIBC). Patients received mostly surgery plus adjuvant therapy (67.7%). BCG (32.8% patients) was the most frequently administered adjuvant therapy, followed by intravesical chemotherapy (17.8% patients) and radiotherapy (10.8%). The variability of administered treatments among hospitals was low. Patients with NMIBC were more likely to receive adjuvant therapy if they had a higher educational level, some comorbidities and a high-grade tumor. The number of fully active patients (ECOG 0) significantly decreased during the first year of follow-up from 58% to 36 % (OR: 2.41, 95%CI 1.82-3.20); at 12-month follow-up 10.8% patients had died from any cause. In conclusion, most of the patients had a NMIBC. Surgery alone or plus adjuvant therapy were the commonest curative options of bladder cancer. BCG therapy was the adjuvant therapy most frequently administered. Higher educational level, presence of comorbidities and a high-grade tumor were associated with adjuvant therapy. Patient performance status was worsening over time. Almost 1 of 10 patients died during the first year of follow-up.

Initial outcomes of a multidisciplinary network for the care of patients with cardiogenic shock.

INTRODUCTION AND OBJECTIVES: Mortality remains high in cardiogenic shock (CS), especially in refractory CS involving the use of mechanical circulatory support (MCS) devices. The aim of this study was to analyze the results of a care program for patients in CS after the creation of a multidisciplinary team in our center and a regional network of hospitals in our area. METHODS: Observational and retrospective study of patients attended in this program from September 2014 to January 2019. We included patients in refractory CS who required MCS and those who, because of their age and absence of comorbidities, were candidates for advanced therapies. The primary endpoint was survival to discharge. RESULTS: A total of 130 patients were included (69 local and 61 transferred patients). The mean age was 52±15 years (72% men). The most frequent causes of CS were acute decompensated heart failure (29%), acute myocardial infarction (26%), and postcardiotomy CS (25%). MCS was used in 105 patients (81%), mostly extracorporeal membrane oxygenation (58%). Survival to discharge was 57% (74 of 130 patients). The most frequent destinations were myocardial recovery and heart transplant. Independent predictors of in-hospital mortality were SAPS II score, lactate level, acute myocardial infarction etiology, and vasoactive-inotropic score. CONCLUSIONS: The creation of multidisciplinary teams for patients with mainly refractory CS and a regional network is feasible and allows survival to discharge in more than a half of attended patients with CS.

Comparison of All-Cause Mortality Following VTE Treatment Between Propensity Score-Adjusted Observational Studies and Matched Randomized Controlled Trials: Meta-Epidemiologic Study.

BACKGROUND: It is unknown whether propensity score-adjusted observational studies produce results comparable to those of randomized controlled trials (RCTs) that address similar VTE treatment issues. METHODS: The PubMed and Web of Science databases were systematically searched for propensity score-adjusted observational studies, RCTs, and meta-analyses of RCTs that estimated all-cause mortality following VTE treatment. After identifying distinct clinical treatment issues evaluated in the eligible observational studies, a standardized algorithm was used to identify and match at least one RCT or RCT meta-analysis publication for paired study design analyses. Meta-analyses were used to summarize groups of studies. Treatment efficacy statistics (relative ORs) were compared between the paired observational and RCT studies, and the summary relative ORs for all study design pairs were also calculated. RESULTS: The observational and RCT study pairs assessed seven clinical treatment issues. Overall, the observational study-RCT pairs did not exhibit significantly different mortality estimates (summary relative OR, 0.89; 95% CI, 0.32-1.46; I2 = 23%). However, two of the seven treatment issue study pairs (thrombolysis vs anticoagulation for pulmonary embolism; once- vs twice-daily enoxaparin for VTE) exhibited a significantly different treatment effect direction, and there was a substantial (nonsignificant) difference in the magnitude of the effect in another two of the study pairs (rivaroxaban vs vitamin K antagonists for VTE; home treatment vs hospitalization for DVT). CONCLUSIONS: This systematic comparison across seven VTE treatment topics suggests that propensity score-adjusted observational studies and RCTs often exhibit similar all-cause mortality, although differences in the direction or the magnitude of estimated treatment effects may occasionally occur. TRIAL REGISTRY: PROSPERO; CRD42018087819; URL: http://www.crd.york.ac.uk/PROSPERO.