Illustrating the Impact of a Time-Varying Covariate With an Extended Kaplan-Meier Estimator

The American Statistician (Impact Factor: 0.98). 02/2005; 59(November):301-307. DOI: 10.1198/000313005X70371
Source: RePEc
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    ABSTRACT: Wide variations in tacrolimus levels have been identified as a risk factor for inferior kidney allograft survival but past studies have not properly accounted for the dynamic nature of drug exposure over time. Here we evaluated whether time-varying exposure to tacrolimus increases the risk of long-term adverse outcomes in a retrospective cohort study in adult kidney transplant recipients on tacrolimus-based immunosuppression. Time-dependent Cox proportional hazards models were used to examine the association between the standard deviation of tacrolimus levels (TacSD) starting at 1-year post-transplant and the composite end point of late allograft rejection, transplant glomerulopathy, or total graft loss (including death). Among 356 patients, there was a significant 27% increase in the adjusted hazard of the composite end point for every 1-unit increase in TacSD (hazard ratio 1.27 (95% confidence interval 1.03, 1.56)). There was also a graded increase in the relative hazard for the composite end point by TacSD threshold (hazard ratios 1.33, 1.50, 1.84, and 2.56 for TacSD 1.5, 2, 2.5, and 3, respectively). The results were similar for total graft loss and the composite end point excluding death. Thus, increased time-dependent TacSD may be an independent risk factor for adverse kidney transplant outcomes. TacSD may serve as a monitoring tool to identify high-risk patients. Whether interventions to decrease TacSD will improve outcomes requires further study.Kidney International advance online publication, 11 December 2013; doi:10.1038/ki.2013.465.
    Kidney International 12/2013; · 8.52 Impact Factor
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    ABSTRACT: Rates of testosterone therapy are increasing and the effects of testosterone therapy on cardiovascular outcomes and mortality are unknown. A recent randomized clinical trial of testosterone therapy in men with a high prevalence of cardiovascular diseases was stopped prematurely due to adverse cardiovascular events raising concerns about testosterone therapy safety. To assess the association between testosterone therapy and all-cause mortality, myocardial infarction (MI), or stroke among male veterans and to determine whether this association is modified by underlying coronary artery disease. A retrospective national cohort study of men with low testosterone levels (<300 ng/dL) who underwent coronary angiography in the Veterans Affairs (VA) system between 2005 and 2011. Primary outcome was a composite of all-cause mortality, MI, and ischemic stroke. Of the 8709 men with a total testosterone level lower than 300 ng/dL, 1223 patients started testosterone therapy after a median of 531 days following coronary angiography. Of the 1710 outcome events, 748 men died, 443 had MIs, and 519 had strokes. Of 7486 patients not receiving testosterone therapy, 681 died, 420 had MIs, and 486 had strokes. Among 1223 patients receiving testosterone therapy, 67 died, 23 had MIs, and 33 had strokes. The absolute rate of events were 19.9% in the no testosterone therapy group vs 25.7% in the testosterone therapy group, with an absolute risk difference of 5.8% (95% CI, -1.4% to 13.1%) at 3 years after coronary angiography. In Cox proportional hazards models adjusting for the presence of coronary artery disease, testosterone therapy use as a time-varying covariate was associated with increased risk of adverse outcomes (hazard ratio, 1.29; 95% CI, 1.04 to 1.58). There was no significant difference in the effect size of testosterone therapy among those with and without coronary artery disease (test for interaction, P = .41). Among a cohort of men in the VA health care system who underwent coronary angiography and had a low serum testosterone level, the use of testosterone therapy was associated with increased risk of adverse outcomes. These findings may inform the discussion about the potential risks of testosterone therapy.
    JAMA The Journal of the American Medical Association 11/2013; 310(17):1829-36. · 29.98 Impact Factor
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    ABSTRACT: Background:Although the prognosis of most patients presenting with malignant pleural mesothelioma (MPM) is poor, a small proportion survives long term. We investigated factors associated with survival in a large patient series.Methods:All patients registered with the NSW Dust Diseases Board (2002-2009) were included in an analysis of prognostic factors using Kaplan-Meier and Cox regression analysis. On the basis of these analyses, we developed a risk score (Prognostic Index (PI)).Results:We identified 910 patients: 90% male; histology (epithelioid 60%; biphasic 13%; sarcomatoid 17%); stage (Tx-I-II 48%; III-IV 52%); and calretinin expression (91%). Treatment: chemotherapy(CT) 44%, and extrapleural-pneumonectomy (EPP) 6%. Median overall survival (OS) was 10.0 months. Longer OS was associated with: age <70 (13.5 vs 8.5 months; P<0.001); female gender (12.0 vs 9.9 months; P<0.001); epithelioid subtype (13.3 vs 6.2 months; P<0.001); ECOG status 0 (27.4 vs 9.7 months; P=0.015), calretinin expression (10.9 vs 5.5 months; P<0.001); neutrophil-lymphocyte ratio (NLR) <5 (11.9 vs 7.5 months; P<0.001); platelet count <400 (11.5 vs 7.2 months; P<0.001); and normal haemoglobin (16.4 vs 8.8 months; P<0.001). On time-dependent analysis, patients receiving pemetrexed-based chemotherapy (HR=0.83; P=0.048) or EPP (HR=0.41; P<0.001) had improved survival. Age, gender, histology, calretinin and haematological factors remained significant on multivariate analysis. In all, 24% of patients survived >20 months: 16% of these receiving EPP, and 66% CT. The PI offered improved prognostic discrimination over one of the existing prognostic models (EORTC).Conclusions:We identified calretinin expression, age, gender, histological subtype, platelet count and haemoglobin level as independent prognostic factors. Patients undergoing EPP or pemetrexed-based chemotherapy demonstrated better survival, but 84% and 34% of long survivors, respectively, did not receive radical surgery or chemotherapy.British Journal of Cancer advance online publication, 4 September 2014; doi:10.1038/bjc.2014.478
    British Journal of Cancer 09/2014; · 4.82 Impact Factor