Generalized mean residual life models for survival data with missing censoring indicators

The mean residual life (MRL) function is an important and attractive alternative to the hazard function for characterizing the distribution of a time-to-event variable. In this article, we study the modeling and inference of a family of generalized MRL models for right-censored survival data with censoring indicators missing at random. To estimate the model parameters, augmented inverse probability weighted estimating equation approaches are developed, in which the non-missingness probability and the conditional probability of an uncensored observation are estimated by parametric methods or nonparametric kernel smoothing techniques. Asymptotic properties of the proposed estimators are established and finite sample performance is evaluated by extensive simulation studies. An application to brain cancer data is presented to illustrate the proposed methods.

GYNOCARE Update: Modern Strategies to Improve Diagnosis and Treatment of Rare Gynecologic Tumors—Current Challenges and Future Directions

Simple Summary

More than 50% of all the tumors affecting the female genital tract can be classified as rare and usually have a poor prognosis owing to delayed diagnosis and treatment. Currently, gynecologic cancer research, due to distinct scientific and technological challenges, is lagging behind. Moreover, the overall efforts for addressing these challenges are fragmented across different countries. The European Network for Gynecological Rare Cancer Research: GYNOCARE aims to address these challenges by creating a unique network between key stakeholders covering distinct domains from basic research to cure. GYNOCARE is part of a European Collaboration in Science and Technology (COST) with the aim to focus on the development of new approaches to improve the diagnosis and treatment of rare gynecological tumors. Here, we provide a brief overview describing the goals of this COST Action and its future challenges with the aim to continue fighting against this rare cancer.

Abstract

More than 50% of all gynecologic tumors can be classified as rare (defined as an incidence of ≤6 per 100,000 women) and usually have a poor prognosis owing to delayed diagnosis and treatment. In contrast to almost all other common solid tumors, the treatment of rare gynecologic tumors (RGT) is often based on expert opinion, retrospective studies, or extrapolation from other tumor sites with similar histology, leading to difficulty in developing guidelines for clinical practice. Currently, gynecologic cancer research, due to distinct scientific and technological challenges, is lagging behind. Moreover, the overall efforts for addressing these challenges are fragmented across different European countries and indeed, worldwide. The GYNOCARE, COST Action CA18117 (European Network for Gynecological Rare Cancer Research) programme aims to address these challenges through the creation of a unique network between key stakeholders covering distinct domains from concept to cure: basic research on RGT, biobanking, bridging with industry, and setting up the legal and regulatory requirements for international innovative clinical trials. On this basis, members of this COST Action, (Working Group 1, “Basic and Translational Research on Rare Gynecological Cancer”) have decided to focus their future efforts on the development of new approaches to improve the diagnosis and treatment of RGT. Here, we provide a brief overview of the current state-of-the-art and describe the goals of this COST Action and its future challenges with the aim to stimulate discussion and promote synergy across scientists engaged in the fight against this rare cancer worldwide.

Expanded findings from a randomized controlled trial of preconception low-dose aspirin and pregnancy loss

STUDY QUESTION

What is the association between daily preconception-initiated low-dose aspirin (LDA) treatment and very early pregnancy losses or euploid (chromosomally normal) losses among women with one to two prior losses?

SUMMARY ANSWER

Daily LDA initiated preconception was not associated with the rate or type of pregnancy loss among women with a history of one to two prior pregnancy losses.

WHAT IS KNOWN ALREADY

LDA is often used to treat recurrent pregnancy loss with reductions in pregnancy loss generally only observed among women with antiphospholipid antibodies, and null associations observed among women without antiphospholipid antibodies. We previously evaluated the association between LDA and pregnancy loss overall among women with one to two prior losses in the Effects of Aspirin in Gestation and Reproduction (EAGeR) trial and found no association, though did not distinguish between potential effects at different stages of pregnancy loss, including implantation failure, or between euploid and aneuploid losses.

STUDY DESIGN, SIZE, DURATION

The EAGeR trial was a multi-site prospective block-randomized double-blind placebo-controlled trial. In total, 1228 women were randomized to daily LDA (81 mg/day) plus folic acid (400 mcg/day), or placebo plus folic acid. Participants were assigned study drug for less than or equal to six menstrual cycles or if they conceived, throughout pregnancy with study drug discontinued at 36 weeks gestation. This analysis includes additional outcome information obtained from chart abstractions after the completion of the trial, as well as testing of stored urine for measurement of hCG and detection of very early pregnancy losses, and karyotyping of the products of conception for assessment of aneuploidy of the losses.

PARTICIPANTS, SETTING, METHODS

Women aged 18-40 with a history of one to two prior losses and actively trying to conceive were randomized (n = 615 LDA and n = 613 placebo) at four clinical centers in the USA (2007-2011). Log-binomial regression was used to estimate risk ratios under the intent-to-treat approach.

MAIN RESULTS AND THE ROLE OF CHANCE

Daily LDA initiated preconception was not associated with clinically recognized pregnancy losses or implantation failures among women with proved fecundity and a history of one to two prior losses. Specifically, 1088 (88.6%) women completed the trial with 797 having an hCG detected pregnancy (64.9%). Overall there were 133 clinical losses (12.7% LDA versus 11.8% placebo, P = 0.71) and 55 implantation failures (5.2% LDA versus 4.9% placebo, P = 0.89). No differences were found in rate of euploid losses (RR 1.11, 95% confidence interval: 0.99, 1.26).

LIMITATIONS, REASONS FOR CAUTION

Generalizability of these findings is limited to women with a history of one to two prior losses, and may further be limited to women of white race with higher socioeconomic status as given the rigors of the study protocol participants tended to be white and have higher incomes and more education. We were also missing karyotype information on approximately one-third of the clinically recognized pregnancy losses, which may limit our power to detect effects on euploid losses, though detailed sensitivity analysis showed similar results.

WIDER IMPLICATIONS OF THE FINDINGS

Our data do not support the general use of LDA to decrease pregnancy loss and further demonstrate no increased risk of loss for women on LDA treatment.

STUDY FUNDING/COMPETING INTERESTS

This research was supported by the Intramural Research Program of the Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland (Contract Nos. HHSN267200603423, HHSN267200603424, HHSN267200603426). The authors have no conflicts of interest.

TRIAL REGISTRATION NUMBER

The trial was registered at ClinicalTrials.gov #NCT00467363.

TRIAL REGISTRATION DATE

27 April 2007.

DATE OF FIRST PATIENT'S ENROLLMENT

15 June 2007.

Sex ratio following preconception low-dose aspirin in women with prior pregnancy loss

BACKGROUND

Several lines of evidence suggest that male embryos may have greater vulnerability than female embryos to disordered inflammation; therefore, antiinflammatory drugs, such as low-dose aspirin (LDA), may alter the sex ratio. Here, we assessed the effect of LDA on male live birth and male offspring, incorporating pregnancy losses (n = 56) via genetic assessment, as part of a parallel-design, block-randomized, placebo-controlled trial of preconception LDA.

METHODS

Participants (615 treated with LDA, 613 treated with placebo) ranged in age from 18 to 40 years of age, with 1 to 2 prior pregnancy losses. We estimated the intention-to-treat (ITT) risk ratio (RR) and 95% CI and assessed interaction with baseline high-sensitivity C-reactive protein (hsCRP) serum concentration - a marker of systemic inflammation.

RESULTS

Among the 1,078 women who completed follow-up (535 treated with LDA, 543 treated with placebo), the male live birth ITT RR equaled 1.31 (95% CI: 1.07-1.59). With increasing tertile of hsCRP, the proportion of males at birth decreased in the placebo group, and the effect of LDA on male live birth increased (first tertile: 48% male in LDA vs. 52% in placebo, ITT RR = 0.97, 95% CI: 0.70-1.35; second tertile: 57% male in LDA vs. 43% in placebo, ITT RR = 1.36, 95% CI: 0.98-1.90; third tertile: 53% male in LDA vs. 35% in placebo, ITT RR = 1.70, 95% CI: 1.13-2.57; P interaction = 0.03). Analysis of pregnancy with male offspring yielded similar results.

CONCLUSION

Initiation of LDA prior to conception restored numbers of male live births and pregnancy with male offspring among women with 1 to 2 prior pregnancy losses. Moreover, our data suggest that LDA modulates inflammation that would otherwise reduce the conception or survival of male embryos.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00467363.

FUNDING

Intramural Research Program of the Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health.

Preconception low dose aspirin and time to pregnancy: findings from the effects of aspirin in gestation and reproduction randomized trial

OBJECTIVE

The objective was to determine the effect of preconception-initiated daily low-dose aspirin (LDA; 81 mg/day) treatment on time to pregnancy in women with a history of pregnancy loss.

DESIGN

This was a multicenter, block-randomized, double-blind, placebo-controlled trial. Participants were block-randomized by center and eligibility stratum.

SETTING

The study was conducted at four U.S.A. medical centers (2007-2012).

PARTICIPANTS

Participants women aged 18-40 years actively attempting pregnancy, stratified by eligibility criteria: the "original" stratum, women with one loss <20 weeks' gestation during the previous year; and the "expanded" stratum, women with one or two previous losses of any gestational age regardless of time since loss.

INTERVENTION

Daily LDA was compared with matching placebo for up to six menstrual cycles of attempting pregnancy.

MAIN OUTCOME MEASURE

Time to hCG detected pregnancy and clinically confirmed pregnancy, analyzed by intention-to-treat, was measured.

RESULTS

Of the 1228 women randomly assigned to LDA (n = 615) or placebo (n = 613), 410 (67%) women receiving LDA achieved pregnancy compared to 382 (63%) receiving placebo, corresponding to a fecundability odds ratio (FOR) of 1.14 (95% CI: 0.97, 1.33). Among women in the original stratum (n = 541), LDA was associated with increased fecundability compared to placebo (FOR: 1.28; 95%CI: 1.02, 1.62).

CONCLUSIONS

Preconception-initiated LDA treatment resulted in a nonsignificant increase in fecundability of 14% in women with a history of 1-2 pregnancy losses, and a significant increase of 28% in women with a history of only one pregnancy loss of <20 weeks' gestation in the preceding year. Preconception-initiated LDA may increase fecundability in certain women with a recent early pregnancy loss.

Low-dose aspirin and preterm birth: a randomized controlled trial

OBJECTIVE

To evaluate the association between low-dose aspirin initiated before conception and the risk of preterm birth.

METHODS

This was a secondary analysis of the Effects of Aspirin in Gestation and Reproduction trial. Women with a history of pregnancy loss (original stratum: one loss less than 20 weeks of gestation during the previous year; expanded stratum: one or two losses with no restrictions on timing or gestational age of the losses) were randomized to either daily low-dose aspirin (81 mg, n=615) and folic acid or folic acid alone (placebo; n=613). Preterm birth was compared between groups using intent-to-treat analysis.

RESULTS

Preterm birth rates were 4.1% (22/535 low-dose aspirin) and 5.7% (31/543 placebo) (relative risk [RR] 0.72, 95% confidence interval [CI] 0.42-1.23); spontaneous preterm birth rates were 1.1% (6/535 low-dose aspirin) and 2.2% (12/543 placebo) (RR 0.51, 95% CI 0.19-1.34); medically indicated preterm birth rates were 2.6% (14/535 low-dose aspirin) and 2.9% (16/543 placebo) (RR 0.89, 95% CI 0.44-1.80). After restriction to confirmed pregnancies using inverse probability weighting, preterm birth rates were 5.7% and 9.0% (RR 0.63, 95% CI 0.37-1.09) and spontaneous preterm birth rates were 1.4% and 3.2% (RR 0.44, 95% CI 0.17-1.18). In confirmed pregnancies in the original stratum, preterm birth occurred in 3.8% and 9.7% of the low-dose aspirin and placebo groups, respectively (RR 0.39, 95% CI 0.16-0.94).

CONCLUSION

Preconception low-dose aspirin was not significantly associated with the overall rate of preterm birth. Although the study was underpowered for this secondary analysis, numeric trends in favor of benefit, particularly in the women with a recent, single early pregnancy loss, warrant further investigation.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov, www.clinicaltrials.gov, NCT00467363.

The effect of a very short interpregnancy interval and pregnancy outcomes following a previous pregnancy loss

OBJECTIVE

We sought to assess the relationship between a short interpregnancy interval (IPI) following a pregnancy loss and subsequent live birth and pregnancy outcomes.

STUDY DESIGN

A secondary analysis of women enrolled in the Effects of Aspirin in Gestation and Reproduction trial with a human chorionic gonadotropin-positive pregnancy test and whose last reproductive outcome was a loss were included in this analysis (n = 677). IPI was defined as the time between last pregnancy loss and last menstrual period of the current pregnancy and categorized by 3-month intervals. Pregnancy outcomes include live birth, pregnancy loss, and any pregnancy complications. These were compared between IPI groups using multivariate relative risk estimation by Poisson regression.

RESULTS

Demographic characteristics were similar between IPI groups. The mean gestational age of prior pregnancy loss was 8.6 ± 2.8 weeks. The overall live birth rate was 76.5%, with similar live birth rates between those with IPI ≤3 months as compared to IPI >3 months (adjusted relative risk [aRR], 1.07; 95% confidence interval [CI], 0.98-1.16). Rates were also similar for periimplantation loss (aRR, 0.95; 95% CI, 0.51-1.80), clinically confirmed loss (aRR, 0.75; 95% CI, 0.51-1.10), and any pregnancy complication (aRR, 0.88; 95% CI, 0.71-1.09) for those with IPI ≤3 months as compared to IPI >3 months.

CONCLUSION

Live birth rates and adverse pregnancy outcomes, including pregnancy loss, were not associated with a very short IPI after a prior pregnancy loss. The traditional recommendation to wait at least 3 months after a pregnancy loss before attempting a new pregnancy may not be warranted.

Preconception low-dose aspirin and pregnancy outcomes: results from the EAGeR randomised trial

BACKGROUND

Preconception-initiated low-dose aspirin might positively affect pregnancy outcomes, but this possibility has not been adequately assessed. Our aim was to investigate whether low-dose aspirin improved livebirth rates in women with one to two previous pregnancy losses.

METHODS

In this multicentre, block-randomised, double-blind, placebo-controlled trial, women aged 18-40 years who were attempting to become pregnant were recruited from four medical centres in the USA. Participants were stratified by eligibility criteria--the original stratum was restricted to women with one loss at less than 20 weeks' gestation during the previous year, whereas the expanded stratum included women with one to two previous losses, with no restrictions on gestational age or time of loss. Women were block-randomised by centre and eligibility stratum in a 1:1 ratio. Preconception-initiated daily low-dose aspirin (81 mg per day) plus folic acid was compared with placebo plus folic acid for up to six menstrual cycles; for women who conceived, study treatment continued until 36 weeks' gestation. Participants, trial staff, and investigators were masked to the assigned treatment. The primary outcome was livebirth rate, which was analysed by intention to treat. The trial is registered with ClinicalTrials.gov, number NCT00467363.

FINDINGS

Overall, 1228 women were recruited and randomly assigned between June 15, 2007, and July 15, 2011, 1078 of whom completed the trial and were included in the analysis (535 in the low-dose aspirin group and 543 in the placebo group). 309 (58%) women in the low-dose aspirin group had livebirths, compared with 286 (53%) in the placebo group (p=0·0984; absolute difference in livebirth rate 5·09% [95% CI -0·84 to 11·02]). Pregnancy loss occurred in 68 (13%) women in the low-dose aspirin group, compared with 65 (12%) women in the placebo group (p=0·7812). In the original stratum, 151 (62%) of 242 women in the low-dose aspirin group had livebirths, compared with 133 (53%) of 250 in the placebo group (p=0·0446; absolute difference in livebirth rate 9·20% [0·51 to 17·89]). In the expanded stratum, 158 (54%) of 293 women in the low-dose aspirin group and 153 (52%) of 293 in the placebo group had livebirths (p=0·7406; absolute difference in livebirth rate 1·71% [-6·37 to 9·79]). Major adverse events were similar between treatment groups. Low-dose aspirin was associated with increased vaginal bleeding, but this adverse event was not associated with pregnancy loss.

INTERPRETATION

Preconception-initiated low-dose aspirin was not significantly associated with livebirth or pregnancy loss in women with one to two previous losses. However, higher livebirth rates were seen in women with a single documented loss at less than 20 weeks' gestation during the previous year. Low-dose aspirin is not recommended for the prevention of pregnancy loss.

FUNDING

Eunice Kennedy Shriver National Institute of Child Health and Human Development (US National Institutes of Health).

A randomised trial to evaluate the effects of low-dose aspirin in gestation and reproduction: design and baseline characteristics

BACKGROUND

Low-dose aspirin (LDA) has been proposed to improve pregnancy outcomes in couples experiencing recurrent pregnancy loss. However, results from studies of LDA on pregnancy outcomes have been inconsistent, perhaps because most studies evaluated LDA-initiated post-conception. The purpose of the Effects of Aspirin in Gestation and Reproduction (EAGeR) trial was to determine whether preconception-initiated LDA improves livebirth rates in women with one to two prior losses.

METHODS

We performed a multicentre, block randomised, double-blind, placebo-controlled trial. Study participants were recruited using community-based advertisements and physician referral to four university medical centres in the US (2006-12). Eligible women were aged 18-40 years actively trying to conceive, with one to two prior losses. Participants were randomised to receive daily LDA (81 mg/day) or a matching placebo, and all were provided with daily 400-mcg folic acid. Follow-up continued for ≤6 menstrual cycles while attempting to conceive. For those who conceived, treatment was continued until 36 weeks gestation. The primary outcome was the cumulative livebirth rate over the trial period.

RESULTS

There were 1228 women randomised (615 LDA, 613 placebo). Participants had a mean age of 28.7, were mostly white (95%), well educated (86% more than high school education), and employed (75%) with a household income >$100 000 annually (40%). The characteristics of those in the treatment and placebo arms were well balanced.

CONCLUSIONS

We describe the study design, recruitment, data collection, and baseline characteristics of participants enrolled in EAGeR, which aimed to determine the effect of LDA on livebirth and other pregnancy outcomes in these women.

Estimation of the ROC curve under verification bias

The ROC (receiver operating characteristic) curve is the most commonly used statistical tool for describing the discriminatory accuracy of a diagnostic test. Classical estimation of the ROC curve relies on data from a simple random sample from the target population. In practice, estimation is often complicated due to not all subjects undergoing a definitive assessment of disease status (verification). Estimation of the ROC curve based on data only from subjects with verified disease status may be badly biased. In this work we investigate the properties of the doubly robust (DR) method for estimating the ROC curve under verification bias originally developed by Rotnitzky, Faraggi and Schisterman (2006) for estimating the area under the ROC curve. The DR method can be applied for continuous scaled tests and allows for a non-ignorable process of selection to verification. We develop the estimator's asymptotic distribution and examine its finite sample properties via a simulation study. We exemplify the DR procedure for estimation of ROC curves with data collected on patients undergoing electron beam computer tomography, a diagnostic test for calcification of the arteries.

Heart rate variability (HRV) of patients with traumatic brain injury (TBI) during the post-insult sub-acute period

OBJECTIVE

To evaluate heart rate variability (HRV) of patients with traumatic brain injury (TBI).

METHODS

By a prospective study, the HRV was assessed in 20 patients with TBI during the sub-acute period post-injury (the first test was performed at a mean time post-insult of 38 days) and a matched control. The patients were examined twice, 1 month apart. The assessment included HRV (both in time and frequency domains), GCS, length of coma, brain CT, FIM and FAM.

RESULTS

A significant difference was found between patients and controls concerning HRV total power, i.e. frequencies between 0.01-0.6 Hz (high frequency p = 0.003, low frequency p = 0.013, total power p = 0.034) and for standard deviation of RR interval p = 0.011. HRV changes were related more to the timing of the evaluation than to the severity of the brain damage.

CONCLUSION

HRV differed of patients with TBI and in the control group. Tendency to HRV normalization changes was detected during the first 3 months after the injury, which suggests recovery of the autonomic nervous system.

Youden Index and the optimal threshold for markers with mass at zero

The Youden Index is often used as a summary measure of the receiver operating characteristic curve. It measures the effectiveness of a diagnostic marker and permits the selection of an optimal threshold value or cutoff point for the biomarker of interest. Some markers, while basically continuous and positive, have a spike or positive mass of probability at the value zero. We provide a flexible modeling approach for estimating the Youden Index and its associated cutoff point for such spiked data and compare it with the standard empirical approach. We show how this modeling approach can be adjusted to take covariate information into account. This approach is applied to data on the Coronary Calcium Score, a marker for atherosclerosis.

Diabetes, but not the metabolic syndrome, predicts the severity and extent of coronary artery disease in women

BACKGROUND

Previous studies have suggested that diabetes and metabolic syndrome are significant risk factors for coronary artery disease (CAD). However, in women, their relative importance remains controversial.

AIM

To evaluate risk factors for CAD in women and their association with the severity and extent of coronary angiographic findings.

METHODS

We clinically evaluated 243 consecutive female patients with chest pain who underwent coronary angiography. The location and extent of coronary artery occlusions were assessed using the modified Gensini index.

RESULTS

Compared with women with normal coronary arteries (n = 90), those with CAD (n = 153) reported less physical activity (p = 0.001), and had higher prevalences of diabetes (p = 0.046), hypertension (p = 0.002), and the metabolic syndrome (p = 0.001). They also had lower HDL cholesterol levels (p = 0.017), higher levels of triglycerides (p = 0.005), and higher fasting plasma glucose (FPG) (p < 0.001). Physical activity, FPG, serum triglycerides and HDL-cholesterol, but not the metabolic syndrome, were independent predictors of CAD. A score combining the extent and severity of angiographic findings was significantly higher in women with diabetes (p = 0.007), hypertension (p = 0.010) and FPG >or=100 mg/dl (p = 0.031), but showed no association with the metabolic syndrome. In a multivariate linear regression analysis, diabetes was an independent predictor of the extent and severity of angiographic score (p = 0.013).

DISCUSSION

Diabetes, fasting plasma glucose and hypertension, but not the metabolic syndrome, were associated with severity of coronary angiographic findings in these women.

Comparing the areas under two correlated ROC curves: parametric and non-parametric approaches

In order to compare the discriminatory effectiveness of two diagnostic markers the equality of the areas under the respective Receiver Operating Characteristic Curves is commonly tested. A non-parametric test based on the Mann-Whitney statistic is generally used. Weiand et al. (1989) present a parametric test based on normal distributional assumptions. We extend this test using the Box-Cox power family of transformations to non-normal situations. These three test procedures are compared in terms of significance level and power by means of a large simulation study. Overall we find that transforming to normality is to be preferred. An example of two pancreatic cancer serum biomarkers is used to illustrate the methodology.

Comparing the areas under two correlated ROC curves: parametric and non-parametric approaches

In order to compare the discriminatory effectiveness of two diagnostic markers the equality of the areas under the respective Receiver Operating Characteristic Curves is commonly tested. A non-parametric test based on the Mann-Whitney statistic is generally used. Weiand et al. (1989) present a parametric test based on normal distributional assumptions. We extend this test using the Box-Cox power family of transformations to non-normal situations. These three test procedures are compared in terms of significance level and power by means of a large simulation study. Overall we find that transforming to normality is to be preferred. An example of two pancreatic cancer serum biomarkers is used to illustrate the methodology.

ROC analysis for markers with mass at zero

The receiver operating characteristic (ROC) curve and in particular the area under the curve (AUC) is commonly used to examine the discriminatory ability of diagnostic markers. Certain markers while basically continuous and non-negative have a positive probability mass (spike) at the value zero. We discuss a flexible modelling approach to such data and contrast it with the standard non-parametric approach. We show how the modelling approach can be extended to take account of the effect of explanatory variables. We motivate this problem and illustrate the modelling approach using data on the coronary calcium score, measured by electron beam tomography, which is a marker for atherosclerosis.

Estimation of the Youden Index and its associated cutoff point

The Youden Index is a frequently used summary measure of the ROC (Receiver Operating Characteristic) curve. It both, measures the effectiveness of a diagnostic marker and enables the selection of an optimal threshold value (cutoff point) for the marker. In this paper we compare several estimation procedures for the Youden Index and its associated cutoff point. These are based on (1) normal assumptions; (2) transformations to normality; (3) the empirical distribution function; (4) kernel smoothing. These are compared in terms of bias and root mean square error in a large variety of scenarios by means of an extensive simulation study. We find that the empirical method which is the most commonly used has the overall worst performance. In the estimation of the Youden Index the kernel is generally the best unless the data can be well transformed to achieve normality whereas in estimation of the optimal threshold value results are more variable.

Reduced glomerular filtration rate in asymptomatic diabetic patients: predictor of increased risk for cardiac events independent of albuminuria

OBJECTIVES

This study aimed to investigate the prevalence of a reduced glomerular filtration rate (GFR) with and without albuminuria and its ability to predict cardiac events in asymptomatic diabetic patients undergoing stress-rest thallium-201 myocardial perfusion single-photon emission computed tomography.

BACKGROUND

Diabetic patients have a higher prevalence of asymptomatic coronary heart disease. Therefore, identifying predictors of cardiac events in asymptomatic diabetic patients is needed.

METHODS

In 269 asymptomatic patients, baseline evaluation included diabetes-related complications, including creatinine clearance (CrCl) and albuminuria. During follow-up (mean 2.3 +/- 1.0 years), all cardiac events were recorded.

RESULTS

Seventy-seven patients (29%) had a reduced GFR defined by CrCl <60 ml/min/1.73 m(2). Compared with the 177 patients with CrCl >/=60 ml/min/1.73 m(2), the reduced GFR group was older (p < 0.0001), had a longer duration of diabetes (p = 0.002), and had a higher prevalence of albuminuria (p = 0.04). Nevertheless, 35% of the reduced GFR group had normoalbuminuria. Patients with reduced GFR had a significant two-fold increase in total cardiac events (unstable angina, nonfatal myocardial infarction, and cardiac procedures) (25% vs. 13%, p = 0.019), and multivariate analysis found that reduced GFR was an independent predictor of cardiac events (odds ratio [OR] 2.2, 95% confidence interval [CI] 1.1 to 4.46). Other independent predictors of cardiac events included stress-induced abnormal myocardial perfusion imaging (OR 3.1, 95% CI 1.3 to 7.5), an electrocardiographic ischemic response (OR 2.7, 95% CI 1.01 to 7.14), and peripheral artery disease (OR 2.1, 95% CI 1.05 to 4.23); however, albuminuria was not.

CONCLUSIONS

A reduced GFR was common in our group of asymptomatic diabetic patients and was associated with a two-fold increase in cardiac events. Multivariate analysis found that reduced GFR independent of albuminuria was a significant predictor of cardiac events.

Adjusting the generalized ROC curve for covariates

Receiver operating characteristic (ROC) curves and in particular the area under the curve (AUC), are widely used to examine the effectiveness of diagnostic markers. Diagnostic markers and their corresponding ROC curves can be strongly influenced by covariate variables. When several diagnostic markers are available, they can be combined by a best linear combination such that the area under the ROC curve of the combination is maximized among all possible linear combinations. In this paper we discuss covariate effects on this linear combination assuming that the multiple markers, possibly transformed, follow a multivariate normal distribution. The ROC curve of this linear combination when markers are adjusted for covariates is estimated and approximate confidence intervals for the corresponding AUC are derived. An example of two biomarkers of coronary heart disease for which covariate information on age and gender is available is used to illustrate this methodology.

ROC curve analysis for biomarkers based on pooled assessments

Interleukin-6 is a biomarker of inflammation which has been suggested as having potential discriminatory ability for myocardial infarction. Because of its high assaying cost it is very expensive to evaluate this marker. In order to reduce this cost we propose pooling the specimens. In this paper we examine the efficiency of ROC curve analysis, specifically the estimation of the area under the ROC curve, when dealing with pooled data. We study the effect of pooling when there are only a fixed number of individuals available for testing and pooling is carried out to save on the number of assays. Alternatively we examine how many pooled assays of size g are necessary to provide essentially the same information as N individual assays. We measure loss of information by means of the change in root mean square error of the estimate of the area under the ROC curve and study the extent of this loss via a simulation study.

Confidence intervals for the 50 per cent response dose

Confidence intervals for the 50 per cent response dose are usually computed using either the Delta method or Fieller's procedure. Recently, confidence intervals computed by inverting the asymptotic likelihood ratio test have also been recommended. There is some controversy as to which of these methods should be used. By means of an extensive simulation study we examine these methods as well as confidence intervals obtained by the approximate bootstrap confidence (ABC) procedure and an adjusted form of the likelihood ratio based confidence intervals.

Phase II study of gemcitabine combined with radiation therapy in patients with localized, unresectable pancreatic cancer

BACKGROUND AND OBJECTIVES

Gemcitabine is an active agent in pancreatic cancer, with known radiosensitizing properties. Therefore, a phase II study was conducted to evaluate the efficacy of gemcitabine combined with radiation therapy in patients with localized unresectable adenocarcinoma of the pancreas.

METHODS

Weekly gemcitabine at a dose of 1,000 mg/m(2) for 7 weeks was given as an induction phase. Patients who showed both clinical benefit response (CBR) and reduced or stable tumor size on computed tomography (CT) scan entered the chemoradiotherapy phase of the treatment. This consisted of gemcitabine 400 mg/m(2) weekly x3 every 28 days for 2 cycles, given concurrently with radiotherapy, for a total dose of 50.4 Gy in 28 fractions. After completion of radiotherapy, gemcitabine was continued as maintenance.

RESULTS

Twenty patients entered this study. Ten patients (50%) achieved CBR to gemcitabine in the induction phase; these patients had no objective tumor progression and were therefore enrolled in the chemoradiotherapy phase. Four patients (20%) had a partial response, and three patients (15%) underwent pancreatectomy. Two patients had negative surgical margins, and in one patient histologic examination of the residual mass showed only fibrosis. The median survival for the entire group was 8 months, and the median survival has not yet been reached for the chemoradiotherapy group.

CONCLUSIONS

Treatment with gemcitabine concomitant with radiation therapy according to the present schedule is well tolerated and can provide prolonged CBR and disease stabilization in patients with localized, unresectable pancreatic cancer.

Estimation of the area under the ROC curve

The area under the receiver operating characteristic curve is frequently used as a measure for the effectiveness of diagnostic markers. In this paper we discuss and compare estimation procedures for this area. These are based on (i) the Mann-Whitney statistic; (ii) kernel smoothing; (iii) normal assumptions; (iv) empirical transformations to normality. These are compared in terms of bias and root mean square error in a large variety of situations by means of an extensive simulation study. Overall we find that transforming to normality usually is to be preferred except for bimodal cases where kernel methods can be effective.

Minimal and best linear combination of oxidative stress and antioxidant biomarkers to discriminate cardiovascular disease

BACKGROUND AND AIM

Free radicals have been implicated in the atherosclerotic process of coronary heart disease (CHD). Well-developed laboratory methods may make available a large number of biomarkers of individual oxidative stress and antioxidant status. Such markers are able to quantify different phases of the oxidative stress and antioxidant status of an individual. However, limited knowledge is available on how to combine these biomarkers to best discriminate between individuals with and without CHD.

METHODS AND RESULTS

We evaluated combined discrimination properties of six biomarkers of oxidative stress and antioxidant status, as indicators of CHD, in a cross-sectional random sample of 968 white men and women from Buffalo, New York. Individuals with CHD had significantly higher levels of thiobarbuturic acid reacting substances (TBARS) and uric acid, and significantly lower levels of high-density lipoproteins (HDL) after adjusting for age and gender, when compared to healthy subjects. There were no significant differences in erythrocyte glutathione (GSH), trolox equivalent antioxidant capacity (TEAC), and glutathione peroxidase (GSHPx) levels. TBARS were found to be the best discriminating of the biomarkers when it was individually evaluated. TBARS discriminate 76.2% (95% C.I. 0.66-0.82) of the CHD cases from healthy controls. When combining TBARS, GSH, TEAC, HDL, uric acid and GSHPx, they discriminate 81.5% (95% C.I.: 0.67-0.90) of the area under the curve.

CONCLUSIONS

These preliminary findings suggest that the combination of multiple markers of oxidative stress does not greatly improve ability to differentiate between individuals with and without CHD compared to the use of TBARS alone.

The association of hormone replacement therapy and coronary calcium as determined by electron beam tomography

BACKGROUND

Observational studies have shown that hormone replacement therapy (HRT) is associated with lower coronary heart disease (CHD), and animal studies demonstrate potent antiatherosclerotic estrogen effects. Paradoxically, recent clinical trials have not demonstrated a protective effect. This paradox may be explained by a healthy woman effect bias. Women using HRT have improved health outcomes unrelated to underlying atherosclerotic burden. Examination of the association between coronary calcium (CC), a marker of atherosclerotic plaque burden, and the use of HRT in postmenopausal women may help address this paradox.

METHODS

The study population comprised 641 asymptomatic postmenopausal women, 425 (66%) of whom were taking HRT. Data obtained from a self-administered questionnaire and blood samples were analyzed. Electron beam tomography (EBT) for CC was performed on each subject. Analysis of variance (ANOVA) was used to evaluate adjusted means.

RESULTS

Independent t tests found that age, low-density lipoproteins (LDL), high-density lipoproteins (HDL), body mass index (BMI), vitamin use, coronary calcium score (CCS), coronary calcified volume (CCV), and the number of coronary calcium lesions (CCL) were significantly different between the HRT group and the non-HRT group. However, after controlling for potential confounders, no significant differences were observed in CCS, CCV, or the number of CCL between the HRT and non-HRT groups. Stratifying by BMI shows that obese/overweight women taking HRT have lower adjusted CCS and fewer CCL than the obese/overweight women not taking HRT.

CONCLUSIONS

These findings demonstrate no association between HRT use and CCS, CCV, and CCL after adjusting for measurable confounders in postmenopausal women. Our failure to demonstrate an independent association between HRT use and a marker of atherosclerotic plaque burden suggests that a healthy woman effect may explain the beneficial association between HRT use and CHD in observational studies.

Understanding neural networks using regression trees: an application to multiple myeloma survival data

Neural networks are becoming very popular tools for analysing data. It is however quite difficult to understand the neural network output in terms of the original covariates or input variables. In this paper we provide, using readily available software, an easy way of understanding the output of the neural network using regression trees. We focus on the problem in the context of censored survival data for patients with multiple myeloma, where identifying groups of patients with different prognosis is an important aspect of clinical studies. The use of regression trees to help understand neural networks can be easily applied to uncensored situations.

mROC: a computer program for combining tumour markers in predicting disease states

Receiver operating characteristic (ROC) curves are limited when several diagnostic tests are available, mainly due to the problems of multiplicity and inter-relationships between the different tests. The program presented in this paper uses the generalised ROC criteria, as well as its confidence interval, obtained from the non-central F distribution, as a possible solution to this problem. This criterion corresponds to the best linear combination of the test for which the area under the ROC curve is maximal. Quantified marker values are assumed to follow a multivariate normal distribution but not necessarily with equal variances for two populations. Other options include Box-Cox variable transformations, QQ-plots, interactive graphics associated with changes in sensitivity and specificity as a function of the cut-off. We provide an example to illustrate the usefulness of data transformation and of how linear combination of markers can significantly improve discriminative power. This finding highlights potential difficulties with methods that reject individual markers based on univariate analyses.

TBARS and cardiovascular disease in a population-based sample

BACKGROUND

Oxygen radicals might play a crucial role in the pathogenesis of various diseases, including atherosclerosis. Thiobarbituric acid reaction substances (TBARS), a biomarker of oxidative stress, have been proposed as a summary measure of total circulating oxidation. However, there is no strong indication that circulating levels of TBARS are increased in patients with atherosclerosis.

DESIGN

We evaluated the relation between TBARS and cardiovascular disease (CVD) in a cross-sectional random sample of white men and women from Buffalo, New York.

METHODS

Logistic regression was used to estimate the risk associated with high levels of TBARS. The area under the ROC curve was used to evaluate the discriminating power of TBARS.

RESULTS

After adjusting for age and gender, TBARS levels were significantly higher in those with prevalent CVD (OR= 1.73, 95% CI=1.32-2.38), compared to those without a CVD diagnosis. These OR were almost 50% higher after correcting for measurement error (ME) (OR=1.93, 95% CI=1.07-3.40). The area under the ROC curve was 0.69 (95% CI=0.62-0.77) and when corrected for ME reached 0.80 (95% CI=0.65-0.89).

CONCLUSIONS

Our results indicate that elevated levels of TBARS were associated with increase risk of the prevalence of CVD, but this effect was no longer significant after adjusting for glucose.

Statistical inference for the area under the receiver operating characteristic curve in the presence of random measurement error

The area under the receiver operating characteristic curve is the most commonly used measure of the ability of a biomarker to distinguish between two populations. Some markers are subject to substantial measurement error. Under normality assumptions, the authors develop a confidence interval procedure for the area under the receiver operating characteristic curve that adjusts for measurement error. This procedure assumes the availability of data from a reliability study of the biomarker. A simulation study was used to check the validity of the proposed confidence interval. Furthermore, it was shown that not adjusting for measurement error could result in a serious understatement of the effectiveness of the biomarker.

[The chemotherapeutic treatment of advanced Hodgkin's disease]

Between 1972 and 1994, 121 adult patients with advanced Hodgkin's disease received MOPP (M) combination chemotherapy, MOPP alternating with ABVD (M-A) or MOPP and ABV hybrid (M/A). Radiation therapy was given to 1/3 of them. The median age was 35 years, 58% had stage III and 42% had stage IV disease. Failure-free survival at 10 years was 43.9%. It was 66.7%, 48.4% and 29.9% for patients treated by M/A, M-A and M, respectively. Overall survival at 10 years was 40.8%, and 78.2%, 48% and 27.7% for patients treated by M/A, M-A and M, respectively. Multivariate analysis found age (above or below 65 years) and combination chemotherapy (with or without adriamycin) to be significant prognostic factors. M/A combination was more myelotoxic, while M combination caused more second primaries. Today, 80% of patients with advanced Hodgkin's disease may be cured, with low rate of long-term toxicity.

Reproducibility of p53 immunohistochemistry in bladder tumors. National Cancer Institute, Bladder Tumor Marker Network

The National Cancer Institute Bladder Tumor Marker Network conducted a study to evaluate the reproducibility of immunohistochemistry for measuring p53 expression in bladder tumors. Fifty paraffin blocks (10 from each of the five network institutions) were chosen at random from among high-grade invasive primary bladder tumors. Two sections from each block were sent to each laboratory for staining and scoring, and then all sections were randomly redistributed among the laboratories for a second scoring. Intra- and interlaboratory reproducibility was assessed with regard to both staining and scoring. For overall assessments of p53 positivity, the results demonstrated that intralaboratory reproducibility was quite good. Concordance across the five participating laboratories was high for specimens exhibiting no or minimal nuclear immunostaining of tumor cells or high percentages of tumor cells with nuclear immunoreactivities. However, there was a reduced level of concordance on specimens with percentages of stained tumor cells in an intermediate range. The discordancies were due mainly to staining differences in one of the five laboratories and scoring differences in another laboratory. These results indicate that some caution must be used in comparing results across studies from different groups. Standardization of staining protocols and selection of a uniform threshold for binary interpretation of results may improve assay reproducibility between laboratories.

The effect of random measurement error on receiver operating characteristic (ROC) curves

In this paper confidence intervals for the area under the ROC curve are adjusted for the presence of measurement error. A parametric normal model is assumed. The ratio of intra-individual to inter-individual variance provides a relative measure of the amount of measurement error. An exact adjusted confidence interval is developed for the equal variance case and an approximation is derived for the unequal variance case. We illustrate, using an example, the effect of ignoring the measurement error on the confidence interval for the area and show that the effect can be substantial on the decision as to the diagnostic effectiveness of the marker. We also examine, by means of a simulation study, the coverage probability of the unadjusted confidence interval and show that it can be far from its nominal value when measurement error is present.

Hospitalizations due to falls in Jewish and Arab children in northern Israel

In Israel, there are no epidemiological data regarding nonfatal childhood falls. A retrospective survey was conducted in order to find epidemiological characteristics of childhood falls among the different populations of northern Israel. During the years 1993 through 1995, 3082 children were hospitalized in Rambam Medical Center (RMC) due to injury. The children were subdivided into the four main populations: Jewish and Arab residents of Haifa region (the main metropolitan area) and Jewish and Arab residents of the Galilee region (the rural region). All of the children who suffered injury that required mechanical ventilation and careful assessment were admitted to the PICU. The charts of the children admitted to the PICU were then further studied. The demographic characteristics of all the cases of falls were statistically analyzed and the annual admission rates due to falls were calculated using the national statistical registrations of children in Israel. Falls were responsible for 1049 admissions due to injury, one third of the total number of children who were admitted due to an injury. Most of the children were five years of age or younger. Two thirds of the total childhood falls were of Arabs. The majority of the admissions were of two major sub-populations of northern Israel: Arab residents of Galilee region (66%) and Jewish residents of Haifa region (34%). Higher admission rate was found among Arab children of the Western Galilee district in comparison with Jewish children of the Haifa district. Most of the children who were admitted to the PICU were Arabs: nearly all of these children were from the rural region. More Arab than Jewish children who fell were admitted to the PICU and the majority of these cases were falls from buildings (private houses). Arab children of the rural region were responsible for 95% of the cases. These falls were mainly in staircases (46%) and from balconies (21%), roofs (11%) and windows (11%). The findings of the present study suggest that young Arab rural children in northern Israel are at high risk to a severe injury due to fall. Possible causes are discussed and a preventative intervention is suggested.

[Generalized ROC criteria in the evaluation of several tumor markers]

The main objective of this paper is to present a method of evaluating several tumor markers by using the generalized ROC criterion. This criterion finds the best linear combination of the tumor markers such that the area under the ROC curve is maximized. Confidence intervals for the generalized ROC criteria are also presented. This methodology is applied to 51 patients with advanced colorectal cancer for whom the ACE tumor markers were measured before and during chemotherapy treatment. Two populations were defined according to clinical response to chemotherapy. Each marker taken separately, whether on the raw scale or on the transformed scale, contained 0.5 in the confidence interval and was thus non significant. This was also true for both markers on the raw scale. However, the best linear combination on the logarithms of ACE before and at evaluation gave a significantly better area under the ROC curve. A weighted change in ACE measurements significantly distinguishes between responders and non responders in patients with advanced colorectal cancer. We propose that the methodology presented in this paper be used for the evaluation of several tumor markers.

Lymphocyte subpopulations in patients with multiple primary tumors

BACKGROUND

Cancer patients with single tumors live longer today due to earlier detection and improved treatment methods. For this reason, the authors see more patients who develop a second primary tumor. The etiology of the second tumor can be the same as the first, whether treatment-induced or unknown. The prognoses of these patients usually depend on the behavior of the second tumor.

METHODS

The authors investigated the lymphocyte subset in 88 of the more than 750 patients listed in the tumor registry at their treatment center who had at least one carcinoma of the breast or colon and a second primary of the same or another site. Mononuclear cells were obtained from heparinized blood by the standard fractionation Hypaque gradient centrifugation technique. Helper and suppressor cells were identified by using three murine monoclonal antibodies: CD3 for mature T lymphocytes, CD4 for helper inducer cells, and CD8 for suppressor cytotoxic cells. T-cell subset distribution was evaluated with flow cytometry.

RESULTS

Most values of CD3, CD4, and CD4/CD8 were lower in patients than in healthy controls. The values of CD4 and CD4/CD8 were lower in patients who had a second tumor in the colon rather than in the breast.

CONCLUSIONS

As tumors in patients with a second primary sometimes recur or the patient develops a third primary, the authors are prospectively following their patients to see whether those with immunosuppression have a greater tendency to develop recurrent disease or a third primary.