Statistics of Rare Events.

Rare events can sometime arise in clinical development of treatments. For example, CYPIDES was a single-arm study of the CYP11A1 inhibitor ODM-208 to treat metastatic prostate cancer.1 Preclinical testing of the compound identified elevated thyroid-stimulating hormone (TSH) and bilirubin in rats and dogs. Unusual findings in preclinical testing focus attention and magnify evidence if similar results occur in humans. By analogy, imagine a murder trial in which the only evidence against the defendant arose from a database search of DNA matching the partial profile found at the crime scene. Multiple people could match, so without other evidence, the perpetrator could be any of them.

Effect of HIV Antibody VRC01 on Viral Rebound after Treatment Interruption.

BACKGROUND: The discovery of potent and broadly neutralizing antibodies (bNAbs) against human immunodeficiency virus (HIV) has made passive immunization a potential strategy for the prevention and treatment of HIV infection. We sought to determine whether passive administration of VRC01, a bNAb targeting the HIV CD4-binding site, can safely prevent or delay plasma viral rebound after the discontinuation of antiretroviral therapy (ART). METHODS: We conducted two open-label trials (AIDS Clinical Trials Group [ACTG] A5340 and National Institutes of Health [NIH] 15-I-0140) of the safety, side-effect profile, pharmacokinetic properties, and antiviral activity of VRC01 in persons with HIV infection who were undergoing interruption of ART. RESULTS: A total of 24 participants were enrolled, and one serious alcohol-related adverse event occurred. Viral rebound occurred despite plasma VRC01 concentrations greater than 50 µg per milliliter. The median time to rebound was 4 weeks in the A5340 trial and 5.6 weeks in the NIH trial. Study participants were more likely than historical controls to have viral suppression at week 4 (38% vs. 13%, P=0.04 by a two-sided Fisher's exact test in the A5340 trial; and 80% vs. 13%, P<0.001 by a two-sided Fisher's exact test in the NIH trial) but the difference was not significant at week 8. Analyses of virus populations before ART as well as before and after ART interruption showed that VRC01 exerted pressure on rebounding virus, resulting in restriction of recrudescent viruses and selection for preexisting and emerging antibody neutralization-resistant virus. CONCLUSIONS: VRC01 slightly delayed plasma viral rebound in the trial participants, as compared with historical controls, but it did not maintain viral suppression by week 8. In the small number of participants enrolled in these trials, no safety concerns were identified with passive immunization with a single bNAb (VRC01). (Funded by the National Institute of Allergy and Infectious Diseases and others; ACTG A5340 and NIH 15-I-0140 ClinicalTrials.gov numbers, NCT02463227 and NCT02471326 .).

Pointwise confidence intervals for a survival distribution with small samples or heavy censoring.

We propose a beta product confidence procedure (BPCP) that is a non-parametric confidence procedure for the survival curve at a fixed time for right-censored data assuming independent censoring. In such situations, the Kaplan-Meier estimator is typically used with an asymptotic confidence interval (CI) that can have coverage problems when the number of observed failures is not large, and/or when testing the latter parts of the curve where there are few remaining subjects at risk. The BPCP guarantees central coverage (i.e. ensures that both one-sided error rates are no more than half of the total nominal rate) when there is no censoring (in which case it reduces to the Clopper-Pearson interval) or when there is progressive type II censoring (i.e. when censoring only occurs immediately after failures on fixed proportions of the remaining individuals). For general independent censoring, simulations show that the BPCP maintains central coverage in many situations where competing methods can have very substantial error rate inflation for the lower limit. The BPCP gives asymptotically correct coverage and is asymptotically equivalent to the CI on the Kaplan-Meier estimator using Greenwood's variance. The BPCP may be inverted to create confidence procedures for a quantile of the underlying survival distribution. Because the BPCP is easy to implement, offers protection in settings when other methods fail, and essentially matches other methods when they succeed, it should be the method of choice.

Evidence for HIV-associated B cell exhaustion in a dysfunctional memory B cell compartment in HIV-infected viremic individuals.

Human immunodeficiency virus (HIV) disease leads to impaired B cell and antibody responses through mechanisms that remain poorly defined. A unique memory B cell subpopulation (CD20(hi)/CD27(lo)/CD21(lo)) in human tonsillar tissues was recently defined by the expression of the inhibitory receptor Fc-receptor-like-4 (FCRL4). In this study, we describe a similar B cell subpopulation in the blood of HIV-viremic individuals. FCRL4 expression was increased on B cells of HIV-viremic compared with HIV-aviremic and HIV-negative individuals. It was enriched on B cells with a tissuelike memory phenotype (CD20(hi)/CD27(-)/CD21(lo)) when compared with B cells with a classical memory (CD27(+)) or naive (CD27(-)/CD21(hi)) B cell phenotype. Tissuelike memory B cells expressed patterns of homing and inhibitory receptors similar to those described for antigen-specific T cell exhaustion. The tissuelike memory B cells proliferated poorly in response to B cell stimuli, which is consistent with high-level expression of multiple inhibitory receptors. Immunoglobulin diversities and replication histories were lower in tissuelike, compared with classical, memory B cells, which is consistent with premature exhaustion. Strikingly, HIV-specific responses were enriched in these exhausted tissuelike memory B cells, whereas total immunoglobulin and influenza-specific responses were enriched in classical memory B cells. These data suggest that HIV-associated premature exhaustion of B cells may contribute to poor antibody responses against HIV in infected individuals.

Clinical events in high-risk hypertensive patients randomly assigned to calcium channel blocker versus angiotensin-converting enzyme inhibitor in the antihypertensive and lipid-lowering treatment to prevent heart attack trial.

The Antihypertensive and Lipid-Lowering treatment to prevent Heart Attack Trial (ALLHAT) provides a unique opportunity to compare the long-term relative safety and efficacy of angiotensin-converting enzyme inhibitor and calcium channel blocker-initiated therapy in older hypertensive individuals. Patients were randomized to amlodipine (n=9048) or lisinopril (n=9054). The primary outcome was combined fatal coronary heart disease or nonfatal myocardial infarction, analyzed by intention-to-treat. Secondary outcomes included all-cause mortality, stroke, combined cardiovascular disease (CVD), end-stage renal disease (ESRD), cancer, and gastrointestinal bleeding. Mean follow-up was 4.9 years. Blood pressure control was similar in nonblacks, but not in blacks. No significant differences were found between treatment groups for the primary outcome, all-cause mortality, ESRD, or cancer. Stroke rates were higher on lisinopril in blacks (RR=1.51, 95% CI 1.22 to 1.86) but not in nonblacks (RR=1.07, 95% CI 0.89 to 1.28), and in women (RR=1.45, 95% CI 1.17 to 1.79), but not in men (RR=1.10, 95% CI 0.92 to 1.31). Rates of combined CVD were higher (RR=1.06, 95% CI 1.00 to 1.12) because of higher rates for strokes, peripheral arterial disease, and angina, which were partly offset by lower rates for heart failure (RR=0.87, 95% CI 0.78 to 0.96) on lisinopril compared with amlodipine. Gastrointestinal bleeds and angioedema were higher on lisinopril. Patients with and without baseline coronary heart disease showed similar outcome patterns. We conclude that in hypertensive patients, the risks for coronary events are similar, but for stroke, combined CVD, gastrointestinal bleeding, and angioedema are higher and for heart failure are lower for lisinopril-based compared with amlodipine-based therapy. Some, but not all, of these differences may be explained by less effective blood pressure control in the lisinopril arm.

Clinical trial results applied to management of the individual cancer patient.

The application of clinical trial results to the management of the individual cancer patient is not always straightforward. The results of a clinical trial indicate the "average" effect of an intervention, often expressed in terms of an absolute risk reduction, which is an estimate of the likelihood of benefit for a particular patient. However, within any clinical trial, there might be differences between groups of patients in underlying pathology, genetics, or biology, and some patients might benefit more from a new treatment than others. Thus, within a clinical trial, it might also be useful to group together patients with similar characteristics, and test for subgroup interaction. The test for interaction will indicate whether the magnitude of benefit differs from one prognostic subgroup to the next (a quantitative interaction). Much less common are qualitative interactions, in which a new treatment is beneficial in one subgroup but harmful in another. If the test for subgroup interaction is significant, then the effects of treatment may indeed differ between subgroups of patients, but this should be confirmed in other trials before a treatment is implemented in clinical practice.

Effects of comprehensive lifestyle modification on diet, weight, physical fitness, and blood pressure control: 18-month results of a randomized trial.

BACKGROUND: The main 6-month results from the PREMIER trial showed that comprehensive behavioral intervention programs improve lifestyle behaviors and lower blood pressure. OBJECTIVE: To compare the 18-month effects of 2 multicomponent behavioral interventions versus advice only on hypertension status, lifestyle changes, and blood pressure. DESIGN: Multicenter, 3-arm, randomized trial conducted from January 2000 through November 2002. SETTING: 4 clinical centers and a coordinating center. PATIENTS: 810 adult volunteers with prehypertension or stage 1 hypertension (systolic blood pressure, 120 to 159 mm Hg; diastolic blood pressure, 80 to 95 mm Hg). INTERVENTIONS: A multicomponent behavioral intervention that implemented long-established recommendations ("established"); a multicomponent behavioral intervention that implemented the established recommendations plus the Dietary Approaches to Stop Hypertension (DASH) diet ("established plus DASH"); and advice only. MEASUREMENTS: Lifestyle variables and blood pressure status. Follow-up for blood pressure measurement at 18 months was 94%. RESULTS: Compared with advice only, both behavioral interventions statistically significantly reduced weight, fat intake, and sodium intake. The established plus DASH intervention also statistically significantly increased fruit, vegetable, dairy, fiber, and mineral intakes. Relative to the advice only group, the odds ratios for hypertension at 18 months were 0.83 (95% CI, 0.67 to 1.04) for the established group and 0.77 (CI, 0.62 to 0.97) for the established plus DASH group. Although reductions in absolute blood pressure at 18 months were greater for participants in the established and the established plus DASH groups than for the advice only group, the differences were not statistically significant. LIMITATIONS: The exclusion criteria and the volunteer nature of this cohort may limit generalizability. Although blood pressure is a well-accepted risk factor for cardiovascular disease, the authors were not able to assess intervention effects on clinical cardiovascular events in this limited time and with this sample size. CONCLUSIONS: Over 18 months, persons with prehypertension and stage 1 hypertension can sustain multiple lifestyle modifications that improve control of blood pressure and could reduce the risk for chronic disease.

Randomized trials of breast-conserving therapy versus mastectomy for primary breast cancer: a pooled analysis of updated results.

We have undertaken a pooled analysis of the 6 major randomized trials comparing mastectomy (MT) and breast-conserving therapy (BCT) in the treatment of primary breast cancer. Specifically, these trials compared the 2 most widely used options in local treatment: mastectomy and axillary dissection (MT) versus breast-conserving surgery, axillary dissection, and breast radiotherapy (BCT). The early results of these 6 trials formed the basis for a 1990 National Institutes of Health Consensus statement. However, most of these trials have recently published long-term follow-up results, and this pooled analysis incorporates the updated results of these 6 trials. For each of these trials, the observed number of treatment events was compared with that expected under the null hypothesis, given the number of patients per arm and the total number of events. Approximate odds ratios were computed using the observed and expected number of events, and the variance of the observed number of events. These were then pooled across trials to give overall odds ratios for the risk of locoregional recurrence, total recurrence, and death. Four of the 6 trials show that MT significantly reduces the risk of locoregional recurrence when compared with BCT, and the pooled odds ratio also shows a significant benefit for MT (odds ratio [OR], 1.561; 95% confidence interval [CI], 1.289-1.890; P < 0.001). However, only 1 trial shows a statistically significant benefit for MT in reducing mortality, and the pooled odds ratio shows no significant difference between MT and BCT (OR, 1.070; 95% CI, 0.935-1.224; P = 0.33). This pooled analysis confirms that MT and BCT have comparable effects on mortality, even after long-term follow up. However, BCT is associated with a significantly greater risk of locoregional recurrence.

Premier: a clinical trial of comprehensive lifestyle modification for blood pressure control: rationale, design and baseline characteristics.

PURPOSE: To describe PREMIER, a randomized trial to determine the effects of multi-component lifestyle interventions on blood pressure (BP). METHODS: Participants with above optimal BP through stage 1 hypertension were randomized to: 1) a behavioral lifestyle (BLS) intervention that implements established recommendations, 2) a BLS intervention that implements established recommendations plus the DASH diet, or 3) an advice only standard of care group. The two BLS interventions consist of group and individual counseling sessions for 18 months. The primary outcome is systolic BP at 6 months. Additional outcomes include diastolic BP and homocysteine at 6 months; systolic and diastolic BP at 18 months; fasting lipids, glucose and insulin at 6 and 18 months; and effects in subgroup. CONCLUSION: Results from the PREMIER trial will provide scientific rationale for implementing multi-component behavioral lifestyle intervention programs to control BP and prevent CVD.