Prediction of nonSVR to therapy with pegylated interferon-alpha2a and ribavirin in chronic hepatitis C genotype 1 patients after 4, 8 and 12 weeks of treatment.

In patients with chronic hepatitis C genotype 1, the current algorithm for treatment discontinuation is based on no early virological response (<2 log decline in hepatitis C virus (HCV)-RNA) at 12 weeks. It is important to determine whether prediction of nonsustained virological response (NR) before 12 weeks can be robustly obtained by statistical methods. We used longitudinal discriminant analysis (LDA) to build and cross-validate models including baseline patient characteristics and measurements of serum HCV-RNA in the first 4, 8 or 12 weeks of treatment. The performance of each model was evaluated by the partial AUC (PA) index, exploring the accuracy of prediction in the range of high negative predictive values. Models were compared by computing 95% confidence intervals for the difference in PA indices. NR was best predicted before week 12 by a single HCV-RNA measurement at week 8 taken together with gender, BMI and age (W8 model, PA index = 0.857). This model was not inferior to models that included a measurement at week 12 (PA index = 0.831). The best model obtained with LDA within the first 4 weeks, which included measurements at days 4, 8 and at week 4, was found to be inferior to the week 8 model (PA index = 0.796). These results indicate that lack of sustained viral response is best predicted after 8 weeks of treatment and that waiting until 12 weeks does not improve the prediction.

A modified approach to estimating sample size for simple logistic regression with one continuous covariate.

Different methods for the calculation of sample size for simple logistic regression (LR) with one normally distributed continuous covariate give different results. Sometimes the difference can be large. Furthermore, some methods require the user to specify the prevalence of cases when the covariate equals its population mean, rather than the more natural population prevalence. We focus on two commonly used methods and show through simulations that the power for a given sample size may differ substantially from the nominal value for one method, especially when the covariate effect is large, while the other method performs poorly if the user provides the population prevalence instead of the required parameter. We propose a modification of the method of Hsieh et al. that requires specification of the population prevalence and that employs Schouten's sample size formula for a t-test with unequal variances and group sizes. This approach appears to increase the accuracy of the sample size estimates for LR with one continuous covariate.

Sparing of the brain in neonatal undernutrition: amino acid transport and incorporation into brain and muscle.

Rates of tyrosine and lysine transport and incorporation into protein were measured in control and undernourished weanling rats. Undernutrition was induced by feeding lactating dams a low protein diet (12 percent casein) from birth to day 21. At weaning, body and brain weights of undernourished rats were 50 percent and 88 percent, respectively, of control values. Lysine and tyrosine transport rates into skeletal muscle were reduced by over 75 percent, more than twice the reduction seen in brain. Rates of amino acid incorporation into muscle protein were reduced by approximately 50 percent; the change in rate of incorporation into brain protein was not statistically significant. These data indicate that, in spite of marked retardation of amino acid transport into brain, the brain seems fully capable of maintaining normal rates of protein synthesis.

A historical cohort study on glycemic-control and cancer-risk among patients with diabetes.

AIMS: This population-based historical cohort study examined whether poor glycemic-control (i.e., high glucose and HbA1c blood levels) in patients with diabetes is associated with cancer-risk. METHODS: From a large healthcare database, patients aged 21-89 years, diagnosed with diabetes before January 2002 (prevalent) or during 2002-2010 (incident), were followed for cancer during 2004-2012 (excluding cancers diagnosed within the first 2 years since diabetes diagnosis). Risks of selected cancers (all-sites, colon, breast, lung, prostate, pancreas and liver) were estimated according to glycemic-control in a Cox regression model with time-dependent covariates, adjusted for age, sex, ethnic origin, socioeconomic status, smoking and parity. Missing glucose or HbA1c values were imputed. RESULTS: Among 440,000 patients included in our analysis, cancer was detected more than 2 years after diabetes diagnosis in 26,887 patients (6%) during the follow-up period. Associations of poor glycemic-control with all-sites cancer and most specific cancers were either null or only weak (hazard ratios (HRs) for a 1% HbA1c or a 30 mg/dl glucose increase between 0.94 and 1.09). Exceptions were pancreatic cancer, for which there was a strong positive association (HRs: 1.26-1.51), and prostate cancer, for which there was a moderate negative association (HRs: 0.85-0.96). CONCLUSION: Overall, poor glycemic-control appears to be only weakly associated with cancer-risk, if at all. A substantial part of the positive association with pancreatic cancer is attributable to reverse causation, with the cancer causing poorer glycemic-control prior to its diagnosis. The negative association with prostate cancer may be related to lower PSA levels in those with poor control.

Tyrosine hydroxylase in human adrenal and pheochromocytoma: localization, kinetics, and catecholamine inhibition.

The properties of partially purified tyrosine hydroxylase from six pheochromocytomas were compared with partially purified normal human and bovine adrenal medulla enzyme. Substrate and inhibition kinetics, cofactor requirements, and intracellular localization of the enzyme from normal and tumor chromaffin tissue of humans were similar, as was the amount of enzyme activity per gram of tissue. Contrary to previous reports, the sensitivity to catecholamine inhibition of the pheochromocytoma enzyme from the six tumors studied was similar to that of both human and bovine adrenal medulla tyrosine hydroxylase. These results suggest that the excessive synthesis and secretion of catecholamines in some pheochromocytomas is not the result of a reduced sensitivity of tyrosine hydroxylase to catecholamine inhibition.

Potential impact of genetic testing on cancer prevention trials, using breast cancer as an example.

Using breast cancer as an example, we explored the potential impact that a highly predictive genetic test could have on the design and analysis of cancer prevention trials. We discuss three situations in this article: 1) trials that are in progress when the genetic test first becomes available as a research tool but is not available for general use, 2) trials in progress when the genetic test becomes generally available to the public, and 3) trials that begin after the test becomes generally available. We have concluded that the availability of a highly predictive genetic test will provide impediments to prevention trials in the form of increased noncompliance and also will provide opportunities in the form of new trials that include only persons at very high risk of developing cancer. Such trial designs could, under favorable circumstances, substantially reduce the size, duration, and cost of cancer prevention trials. The availability of a highly predictive genetic test will make the discovery of effective interventions even more urgent, and the randomized trial will still provide the most reliable method of evaluating prevention strategies.

What does it mean to be a cancer gene carrier? Problems in establishing causality from the molecular genetics of cancer.

This article addresses the following question: What does it mean to be a cancer gene carrier? The existence of families prone to cancer has prompted an intense search for predisposing heritable gene mutations. Genes that impart susceptibility to colorectal, breast, and ovarian cancers have been recently identified. It is doubtful, however, that the action of a single mutant gene totally accounts for the development of malignant disease. The mutant gene likely causes cancer in these family members only in conjunction with other genes, environmental factors, or both. Furthermore, although an individual carrier of a mutant gene within a cancer-prone family has an increased risk of malignancy, nutritional, pharmacologic, or other interventions may still confer protection. Extrapolations from cancer-prone families to the general population are even more problematic. The excess risk of malignancy among carriers of mutant genes who are not members of cancer-prone families is unknown. Large-scale epidemiologic studies are needed to determine the magnitude (or even the existence) of such excess risk.

Validation of intermediate end points in cancer research.

Investigations using intermediate end points as cancer surrogates are quicker, smaller, and less expensive than studies that use malignancy as the end point. We present a strategy for determining whether a given biomarker is a valid intermediate end point between an exposure and incidence of cancer. Candidate intermediate end points may be selected from case series, ecologic studies, and animal experiments. Prospective cohort and sometimes case-control studies may be used to quantify the intermediate end point-cancer association. The most appropriate measure of this association is the attributable proportion. The intermediate end point is a valid cancer surrogate if the attributable proportion is close to 1.0, but not if it is close to 0. Usually, the attributable proportion is close to neither 1.0 nor 0; in this case, valid surrogacy requires that the intermediate end point mediate an established exposure-cancer relation. This would in turn imply that the exposure effect would vanish if adjusted for the intermediate end point. We discuss the relative advantages of intervention and observational studies for the validation of intermediate end points. This validation strategy also may be applied to intermediate end points for adverse reproductive outcomes and chronic diseases other than cancer.

Alpha-Tocopherol and beta-carotene supplements and lung cancer incidence in the alpha-tocopherol, beta-carotene cancer prevention study: effects of base-line characteristics and study compliance.

BACKGROUND: Experimental and epidemiologic investigations suggest that alpha-tocopherol (the most prevalent chemical form of vitamin E found in vegetable oils, seeds, grains, nuts, and other foods) and beta-carotene (a plant pigment and major precursor of vitamin A found in many yellow, orange, and dark-green, leafy vegetables and some fruit) might reduce the risk of cancer, particularly lung cancer. The initial findings of the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study (ATBC Study) indicated, however, that lung cancer incidence was increased among participants who received beta-carotene as a supplement. Similar results were recently reported by the Beta-Carotene and Retinol Efficacy Trial (CARET), which tested a combination of beta-carotene and vitamin A. PURPOSE: We examined the effects of alpha-tocopherol and beta-carotene supplementation on the incidence of lung cancer across subgroups of participants in the ATBC Study defined by base-line characteristics (e.g., age, number of cigarettes smoked, dietary or serum vitamin status, and alcohol consumption), by study compliance, and in relation to clinical factors, such as disease stage and histologic type. Our primary purpose was to determine whether the pattern of intervention effects across subgroups could facilitate further interpretation of the main ATBC Study results and shed light on potential mechanisms of action and relevance to other populations. METHODS: A total of 29,133 men aged 50-69 years who smoked five or more cigarettes daily were randomly assigned to receive alpha-tocopherol (50 mg), beta-carotene (20 mg), alpha-tocopherol and beta-carotene, or a placebo daily for 5-8 years (median, 6.1 years). Data regarding smoking and other risk factors for lung cancer and dietary factors were obtained at study entry, along with measurements of serum levels of alpha-tocopherol and beta-carotene. Incident cases of lung cancer (n = 894) were identified through the Finnish Cancer Registry and death certificates. Each lung cancer diagnosis was independently confirmed, and histology or cytology was available for 94% of the cases. Intervention effects were evaluated by use of survival analysis and proportional hazards models. All P values were derived from two-sided statistical tests. RESULTS: No overall effect was observed for lung cancer from alpha-tocopherol supplementation (relative risk [RR] = 0.99; 95% confidence interval [CI] = 0.87-1.13; P = .86, logrank test). beta-Carotene supplementation was associated with increased lung cancer risk (RR = 1.16; 95% CI = 1.02-1.33; P = .02, logrank test). The beta-carotene effect appeared stronger, but not substantially different, in participants who smoked at least 20 cigarettes daily (RR = 1.25; 95% CI = 1.07-1.46) compared with those who smoked five to 19 cigarettes daily (RR = 0.97; 95% CI = 0.76-1.23) and in those with a higher alcohol intake (> or = 11 g of ethanol/day [just under one drink per day]; RR = 1.35; 95% CI = 1.01-1.81) compared with those with a lower intake (RR = 1.03; 95% CI = 0.85-1.24). CONCLUSIONS: Supplementation with alpha-tocopherol or beta-carotene does not prevent lung cancer in older men who smoke. beta-Carotene supplementation at pharmacologic levels may modestly increase lung cancer incidence in cigarette smokers, and this effect may be associated with heavier smoking and higher alcohol intake. IMPLICATIONS: While the most direct way to reduce lung cancer risk is not to smoke tobacco, smokers should avoid high-dose beta-carotene supplementation.

Analysis of dietary fat, calories, body weight, and the development of mammary tumors in rats and mice: a review.

We have extracted from the literature data from 100 animal experiments, involving 7838 rats and mice, which compared the effects of different levels of dietary fat and/or calorie intake on the development of mammary tumors. Both higher calorie intake (P less than 0.0001) and higher fat intake (P less than 0.0001) independently increased mammary tumor incidence in Sprague-Dawley rats and in mice, as judged from analyses combining ad libitum feeding experiments and restricted feeding experiments. The effect of fat was two thirds the magnitude of the calorie effect in both Sprague-Dawley rats and mice. In ad libitum feeding experiments, a modest but significant (P less than 0.0001) average increase in body weight was found in animals fed high fat diets. However, these differences in body weight did not correspond to differences in mammary tumor incidence. The effect of log body weight on the log odds of tumor incidence was not significant (P = 0.16), while dietary fat intake significantly increased tumor incidence (P less than 0.0001). The collection of animal experimental data supports the hypothesis that, in mammary tumor development, there is a specific enhancing effect of dietary fat, as well as a general enhancing effect of calories.

Effect of different types and amounts of fat on the development of mammary tumors in rodents: a review.

We performed a meta-analysis on data extracted from 97 reports of experiments, involving a total of 12,803 mice or rats, studying the effect on mammary tumor incidence of different types of dietary fatty acids. Fatty acids were categorized into saturated, monounsaturated, n-6 polyunsaturated, and n-3 polyunsaturated. We modeled the relation between tumor incidence and percentage of total calories from these fatty acids using conditional logistic regression and allowing for varying effects between experiments, and for each fatty acid we estimated the effect of substituting the fatty acid calories for nonfat calories. Our results show that n-6 polyunsaturated fatty acids (PUFAs) have a strong tumor-enhancing effect and that saturated fats have a weaker tumor-enhancing effect. The n-3 PUFAs have a small protective effect that is not statistically significant. There is no significant effect of monounsaturated fats. n-6 PUFAs have a stronger tumor-enhancing effect at levels under 4% of total calories, but an effect is still present at intake levels greater than 4% of calories. In addition, when the intake of n-6 PUFAs is at least 4% of calories, the n-6 PUFA effect remains stronger than the saturated fat effect.

Statistical design of calibration studies.

We investigated some design aspects of calibration studies. The specific situation addressed was one in which a large group is evaluated with a food-frequency questionnaire and a smaller calibration study is conducted through use of repeated food records or recalls, with the subjects in the calibration study constituting a random sample of those in the large group. In designing a calibration study, one may use large sample sizes and few food records per individual or smaller samples and more records per subject. Neither strategy is always preferable. Instead, the optimal method for a given study depends on the survey instrument used (24-h recalls or multiple-day food records) and the variables of interest.

Register of dietary assessment calibration-validation studies: a status report.

A register of dietary assessment calibration-validation studies was created to improve communication between investigators, avoid duplication of effort, and identify gaps in knowledge. Calibration-validation studies were defined as investigations in which the participants completed at least two different dietary measurements. A questionnaire soliciting descriptive information about such studies was widely distributed. Completed questionnaires were received from October 1993 through September 1994 and the data from them were entered into a computer database. Preliminary individual reports were mailed to all contributors in September 1994 for revision or updating. Responses received by the end of October 1994 were incorporated into the database. A status report was published in December 1994. The report includes descriptions of 84 studies, 15 summary tables, and 6 reference indexes. Of the 84 studies included, 44 (52%) were conducted in North America, 35 (42%) in Europe, 2 (2%) in South America, 2 (2%) in Asia, and 1 (1%) in Australia. Sixty-three of the 84 studies (75%) used food-frequency questionnaires, 52 (62%) used food records, 35 (42%) used one or more dietary recalls, 11 (13%) used biological measures, and 8 (10%) used diet histories. Plans for maintaining and updating the register are being developed.

Randomized, placebo-controlled, double-blind study of low-dose oral interferon-alpha in HIV-1 antibody positive patients.

One hundred forty-nine patients of private physicians in Toronto, Canada, who were positive for human immunodeficiency virus (HIV), medically stable, and had CD4 cell counts of < 700 cells/mm3 participated in a randomized, double-blind trial of placebo versus low-dose (50 U) versus high-dose (100 U) oral interferon-alpha. Treatment allocation was balanced according to baseline CD4 cell count and history of prior antiviral therapy. Patients were observed at 4 and 8 weeks for assessment of adverse events and several measures of disease status, including CD4 cell count, beta 2-microglobulin, weight, and Karnofsky score. We detected neither short-term benefits nor adverse effects from oral interferon-alpha therapy.

Surrogate end points in cancer research: a critique.

Studies using surrogate end points of malignant disease may be smaller, shorter, and less expensive than studies with incident cancer end points. Researchers have proposed a broad range of histological, cellular, and molecular markers as surrogate end points for cancer (SECs). We define a valid SEC as follows: the effect of an intervention on (or the association of a risk factor with) the SEC is concordant with its effect on (or association with) incident cancer. Adenomatous polyps and persistent human papillomavirus infections are examples of reasonably valid SECs (for colorectal and cervical cancer, respectively) because these markers are necessary precursors of most of these malignancies. Inferences from other potential SECs, however, are problematic if there exist major alternative causal pathways to malignancy bypassing the SEC. Furthermore, in such circumstances, an SEC that is valid for one intervention or exposure may not be valid for another. Even for those end points without such major alternative pathways, an intervention could differentially affect two intermediate markers on the same pathway, thus disturbing the concordance between its effect on a given SEC and its effect on cancer. Thus, an understanding of the causal structure underlying the relations of interventions/exposures, potential SECs, and cancer is critical in evaluating SECs. Three questions are pertinent to elucidating this structure: (a) What is the relation of the SEC to cancer? (b) What is the relation of the intervention/exposure to the SEC? and (c) To what extent doses the SEC mediate the relation between the intervention/exposure and cancer? Ecological, metabolic, observational epidemiological, and intervention studies may provide data relevant to one or more of these questions. Data on SEC variability are critical in evaluating whether marker findings have been attenuated by random sources of intra-individual variation. We emphasize the importance of conducting studies, especially SEC-cancer and intervention/exposure-SEC-cancer mediation studies, to evaluate problematic SECs such as epithelial cell hyperproliferation. For some time to come, hard and policy-relevant evidence on cancer etiology and prevention will emerge only from studies with cancer end points or, at a somewhat lower level of certainty, SECs that are (for the most part) obligatory steps on the causal pathway to malignant disease.

The polyp prevention trial I: rationale, design, recruitment, and baseline participant characteristics.

The Polyp Prevention Trial (PPT) is a multicenter randomized controlled trial examining the effect of a low-fat (20% of total energy intake), high-fiber (18 g/1000 kcal), high-vegetable and -fruit (5-8 daily servings) dietary pattern on the recurrence of adenomatous polyps of the large bowel, precursors of most colorectal malignancies. Eligibility criteria include one or more adenomas removed within 6 months of randomization; complete nonsurgical polyp removal and complete colonic examination to the cecum at the qualifying colonoscopy: age 35 years of more; no history of colorectal cancer, inflammatory bowel disease, or large bowel resection; and satisfactory completion of a food frequency questionnaire and 4-day food record. Of approximately 38,277 potential participants with one or more polyps recently resected, investigators at eight clinical centers randomized 2,079 (5.4%; 1,037 in the intervention and 1,042 in the control arm) between June 1991 and January 1994, making the PPT the largest adenoma recurrence trial ever conducted. Of PPT participants, 35% are women and 10% are minorities. At study entry, participants averaged 61.4 years of age; 14% of them smoked, and 22% used aspirin. At the baseline colonoscopy, 35% of participants had two or more adenomas, and 29% had at least one large (> of = 1 cm) adenoma. Demographic, behavioral, dietary, and clinical characteristics are comparable across the two study arms. Participants have repeat colonoscopies after 1 (T(1)) and 4 (T(4)) years of follow-up. The primary end point is adenoma recurrence; secondary end points include number, size, location, and histology of adenomas. All resected lesions are reviewed centrally by gastrointestinal pathologists. The trial provides 90% power to detect a reduction of 24% in the annual adenoma recurrence rate. The primary analytic period, on which sample size calculations were based is 3 years (T(1) to T(4)), which permits a 1-year lag time for the intervention to work and allows a more definitive clearing of lesions at T(1), given that at least 10-15% of polyps may be missed at baseline. The final (T(4)) colonoscopies are expected to be completed in early 1998.

An evaluation of rectal mucosal proliferation measure variability sources in the polyp prevention trial: can we detect informative differences among individuals' proliferation measures amid the noise?

We assessed components of total variability of bromodeoxyuridine (BrdUrd) and proliferating cell nuclear antigen (PCNA) assays of rectal mucosal proliferation in a subset of 390 participants from the U. S. National Cancer Institute's multicenter Polyp Prevention Trial. Biopsies were blindly double-scored by two technicians. For those participants for whom at least one evaluable biopsy was obtained, a mean of 2.0 and 2.6 biopsies, and 6.2 and 8.7 crypts/biopsy were evaluated, respectively, with the BrdUrd and PCNA assays. Factors such as clinical center, scorer, and month of biopsy collection significantly affected the observed values of the labeling index (LI) and proliferative height (PH). Therefore, it is essential to control or adjust for these variables in proliferation studies. Sources of random variation for LI and PH measures remaining after the aforementioned factors include between-participant variation and several sources of within-participant variation, including variation over time, between biopsies, and between multiple measurements on the same biopsy. Both LI and PH measurements exhibited substantial variability over time, between biopsies, and from reading-to-reading of the same biopsy. When other sources of variability have been accounted for, the PCNA LI seems to have little between-participant variation. This brings into question its utility as a marker in colorectal cancer studies. The PCNA PH showed significant between-participant variability and may hold some promise as a useful marker in colorectal cancer studies. Results for BrdUrd were less conclusive. The BrdUrd LI showed marginally significant between-participant variation, whereas the corresponding variation for PH was nonsignificant.

A randomized study of CCNU with and without benznidazole in the treatment of recurrent grades 3 and 4 astrocytoma. Report to the Medical Research Council by the Brain Tumor Working Party.

In a randomized, double-blind study, 44 patients with recurrent high grade malignant glioma were allocated to chemotherapy of CCNU, with or without benznidazole (BENZO). Of 42 eligible patients, 23 received CCNU alone, and 19 CCNU received BENZO. Only 8 patients received the full 6 courses of treatment. The mean number of courses given was 2.8 for placebo and 3.4 for benznidazole patients. Progressive disease caused termination of treatment early for the majority of patients. There was no evidence of increased toxicity-leucopenia, anemia or thrombocytopenia-in the BENZO group, and only one patient in each treatment group had chemotherapy terminated because of toxicity. The BENZO group did not demonstrate any survival advantage: median survival time was 25 weeks in the BENZO group and 30 weeks in the placebo group. The confidence interval for the treatment difference is wide but excludes a BENZO-related addition of more than 7 months to the median survival time.

Bayesian monitoring of phase II trials in cancer chemoprevention.

Early randomized Phase II cancer chemoprevention trials which assess short-term biological activity are critical to the decision process to advance to late Phase II/Phase III trials. We have adapted published Bayesian interim analysis methods (Spiegelhalter et al., J. R. Statist. Soc A, 1994; 157: 357-416) which give greater flexibility and simplicity of inference to the monitoring of randomized controlled Phase II trials using intermediate endpoints. The Bayesian stopping rule is designed to stop the trial more quickly when the evidence suggests ineffectiveness rather than when it suggests biological activity, thus allowing resources to be concentrated on those agents that show the most promise in this early stage of testing. We investigate frequentist performance characteristics of the proposed method through simulation of randomized placebo controlled trials with a growth factor intermediate end-point using mean and variance values derived from the literature. Simulation results show expected error rates and trial size similar to other commonly used group sequential methods for this setting. These results suggest that the Bayesian approach to interim analysis is well suited for monitoring small randomized controlled Phase II chemoprevention trials for early detection of either inactive or promising agents.

Measuring cell proliferation in the rectal mucosa. comparing bromodeoxyuridine (BrdU) and proliferating cell nuclear antigen (PCNA) assays.

Cell proliferation in the human colorectum can be measured using bromodeoxyuridine (BrdU) or proliferating cell nuclear antigen (PCNA) assays. Using data from the National Cancer Institute's Polyp Prevention Trial, these two assays are compared using correlation coefficients and variance components analysis. Adjusting for fixed as well as for the random effects of between-biopsy and scoring variation, the estimated correlation is 0.46 for the log labeling index and 0.45 for log proliferative height. This is an estimate of the highest correlation that can be achieved by taking multiple biopsies scored by multiple scorers. For single biopsies, the estimated correlation is 0.16 and 0.10, respectively. There are significant differences between the variance components for the two assays. For example, for log labeling index, PCNA has a lower variation between biopsies than BrdU, but higher variation between scorings. When used in a clinical or epidemiological setting, it is important to take multiple biopsies at multiple time points.