Competing risks and multivariate outcomes in epidemiological and clinical trial research.

Data analysis methods for the study of treatments or exposures in relation to a clinical outcome in the presence of competing risks have a long history, often with inference targets that are hypothetical, thereby requiring strong assumptions for identifiability with available data. Here data analysis methods are considered that are based on single and higher dimensional marginal hazard rates, quantities that are identifiable under standard independent censoring assumptions. These lead naturally to joint survival function estimators for outcomes of interest, including competing risk outcomes, and provide the basis for addressing a variety of data analysis questions. These methods will be illustrated using simulations and Women's Health Initiative cohort and clinical trial data sets, and additional research needs will be described.

The renin-angiotensin aldosterone system and osteoporosis: findings from the Women's Health Initiative.

New users of RAAS inhibitors, including ACE inhibitors and ARBs, have a small increased risk for fracture in the first 3 years of use, with a reduced risk of fracture with longer duration of use. INTRODUCTION: Pharmacological inhibitors of the renin-angiotensin aldosterone system (RAAS) are used to treat hypertension. However, the relationship of these medications to osteoporosis is inconsistent, and no study has included simultaneous measurements of both incident fractures and bone mineral density (BMD). METHODS: The association of RAAS inhibitor use (n = 131,793) with incident fractures in new users of these medications in women in the Women's Health Initiative over a minimum median follow-up of 6.5 years was assessed by Cox proportional hazard models. The association of incident fractures by a cumulative duration of use of these medications (< 3 years.) and (> 3 years.) was also estimated. Subgroup analysis of fracture risk by RAAS inhibitor use confined to women with hypertension was also performed (n = 33,820). The association of RAAS inhibitor use with changes in BMD of the hip was estimated by linear regression in 8940 women with dual energy X-ray absorptiometry measurements. RESULTS: There was no significant association between RAAS inhibitor use and all fractures in the final adjusted multivariable models including hip BMD (HR 0.86 (0.59, 1.24)). However, among users of RAAS inhibitors, including ACE inhibitors and angiotensin receptor blockers (ARBs), hazard ratios for all incident fracture sites in final multivariable models including hip BMD showed dramatic differences by duration of use, with short duration of use (3 years or less) associated with a marked increased risk for fracture (HR 3.28 (1.66, 6.48)) to (HR 6.23 (3.11, 12.46)) and use for more than 3 years associated with a reduced fracture risk (HR 0.40 (0.24, 0.68) to (HR 0.44 (0.20, 0.97)) . Findings were similar in the subgroup of women with a history of hypertension. There was no significant change in BMD of the hip by RAAS inhibitor use. CONCLUSIONS: In postmenopausal women, use of RAAS inhibitors, including ACE inhibitors and ARBs, is associated with an increased risk for fracture among new users of these medications in the first 3 years of use. However, long-term use (> 3 years) is associated with a reduced risk. Consideration for fracture risk may be part of the decision-making process for initiation of these medications for other disease states.

Reliable evidence from placebo-controlled, randomized, clinical trials for menopausal hormone therapy's influence on incidence and deaths from breast cancer.

In an invited editorial, Dr Shapiro proposes that vaginal bleeding leading to unblinding and subsequent detection bias explains the breast cancer increase seen with estrogen plus progestin in the Women's Health Initiative (WHI) clinical trial (1) . In the context of a uniform detection program of protocol-mandated annual mammography and breast examinations, such a proposal is medically implausible. Dr Shapiro suggests detection bias would identify a larger number of 'slowly growing tumors that would otherwise remain clinically silent'. The findings of more advanced cancers with increased deaths from breast cancer in the estrogen plus progestin group refute this conjecture. During early post-intervention phases of both WHI hormone therapy trials, when breast cancer detection bias is asserted by Dr Shapiro because participants had been informed of randomization assignment, breast cancer incidence rates were lower (rather than higher) than during intervention. Thus, Dr Shapiro's claims are directly refuted by findings from the WHI randomized clinical trials. Health-care providers should be aware that randomized clinical trial evidence supports estrogen plus progestin increasing breast cancer incidence and deaths from breast cancer. In contrast, among women with prior hysterectomy, randomized clinical trial evidence supports estrogen alone reducing breast cancer incidence and deaths from breast cancer.

Health risks and benefits from calcium and vitamin D supplementation: Women's Health Initiative clinical trial and cohort study.

SUMMARY: The Women's Health Initiative (WHI) double-blind, placebo-controlled clinical trial randomly assigned 36,282 postmenopausal women in the U.S. to 1,000 mg elemental calcium carbonate plus 400 IU of vitamin D(3) daily or placebo, with average intervention period of 7.0 years. The trial was designed to test whether calcium plus vitamin D supplementation in a population in which the use of these supplements was widespread would reduce hip fracture, and secondarily, total fracture and colorectal cancer. INTRODUCTION: This study further examines the health benefits and risks of calcium and vitamin D supplementation using WHI data, with emphasis on fractures, cardiovascular disease, cancer, and total mortality. METHODS: WHI calcium and vitamin D randomized clinical trial (CT) data through the end of the intervention period were further analyzed with emphasis on treatment effects in relation to duration of supplementation, and these data were contrasted and combined with corresponding data from the WHI prospective observational study (OS). RESULTS: Among women not taking personal calcium or vitamin D supplements at baseline, the hazard ratio [HR] for hip fracture occurrence in the CT following 5 or more years of calcium and vitamin D supplementation versus placebo was 0.62 (95 % confidence interval (CI), 0.38-1.00). In combined analyses of CT and OS data, the corresponding HR was 0.65 (95 % CI, 0.44-0.98). Supplementation effects were not apparent on the risks of myocardial infarction, coronary heart disease, total heart disease, stroke, overall cardiovascular disease, colorectal cancer, or total mortality, while evidence for a reduction in breast cancer risk and total invasive cancer risk among calcium plus vitamin D users was only suggestive. CONCLUSION: Though based primarily on a subset analysis, long-term use of calcium and vitamin D appears to confer a reduction that may be substantial in the risk of hip fracture among postmenopausal women. Other health benefits and risks of supplementation at doses considered, including an elevation in urinary tract stone formation, appear to be modest and approximately balanced.

Treatment of aplastic anemia by marrow transplantation from HLA identical siblings. Prognostic factors associated with graft versus host disease and survival.

73 consecutive patients with severe aplastic anemia were treated by marrow transplantation from hematologically normal HLA identical siblings. 68 patients lived long enough to document marrow engraftment. 21 rejected the graft and 19 of these died. 47 sustained engraftment and 18 of these died. In 16 patients, death was associated with graft versus host disease. 29 patients with sustained engraftment are alive with complete hematologic restoration between 8 mo and 5 yr. This analysis, by using a proportional hazards regression model, was directed at identifying factors that predicted survival (and absence of graft versus host disease). Of the 24 factors entered into the analysis only two strongly correlated with survival: (a) sex match of donor and recipient (P less than 0.01), and (b) absence of refractoriness to random donor platelets at the time of transplantation (P less than 0.05). Refractoriness adversely influenced the survival of the sex mismatched patients, These data suggest that X and Y-associated transplantation antigen systems are important determinants of the outcome of marrow grafts between HLA identical siblings for the treatment of aplastic anemia. The machanism by which refractoriness to random donor platelets influences survival is currently unclear.

Measurement error and results from analytic epidemiology: dietary fat and breast cancer.

BACKGROUND: International correlational analyses have suggested a strong positive association between fat consumption and breast cancer incidence, especially among post-menopausal women. However, case-control studies have been taken to indicate a weaker association, and a recent, pooled cohort analysis reported little evidence of an association. Differences among study results could be due to differences in the populations studied, differences in the control for total energy intake, recall bias in the case-control studies, and dietary measurement error biases. Existing measurement error models assume either that the sample data used to validate dietary self-report instruments are without measurements error or that any such error is independent of both the true dietary exposure and other study subject characteristics. However, growing evidence indicates that total energy and, presumably, both total fat and percent energy from fat are increasingly underreported as percent body fat increases. PURPOSE: A relaxed dietary measurement model is introduced that allows all measurement error parameters to depend on body mass index (weight in kilograms divided by the square of height in meters) and incorporates a random underreporting quantity that applies to each dietary self-report instrument. The model was applied to results from international correlational analyses to determine whether the differing associations between dietary fat and postmenopausal breast cancer can be explained by measurement errors in dietary assessment. METHODS: The relaxed measurement model was developed by use of data on total fat intake and percent energy from fat from 4-day food records (4DFRs) and food-frequency questionnaires (FFQs) from the original Women's Health Trial. This trial was a randomized, controlled, feasibility study of a low-fat dietary intervention carried out from 1985 through 1988 in Cincinnati (OH), Houston (TX), and Seattle (WA) among 303 women (184 intervention and 119 control) who were 45-69 years of age. The relaxed model was used to project results from the international correlational analyses onto 4DFR and FFQ fat-intake categories. RESULTS AND CONCLUSIONS: If measurement errors in dietary assessment are overlooked entirely, the projected relative risks (RRs) for breast cancer based on the international data vary substantially across percentiles of total fat intake. The projected RR for the 90% versus the 10% fat-intake percentile is 3.08 with the 4DFR and 4.00 with the FFQ. If random (i.e., noise) aspects of measurement error are acknowledged, the projected RR for the same comparison is reduced to 1.54 with the 4DFR and 1.42 with the FFQ. If both systematic and noise aspects of measurement error are acknowledged, the projected RR is reduced to about 1.10 with either instrument. Acknowledgment of measurement error also leads to a projected RR of about 1.10 for the 90% versus the 10% percentile of percent energy from fat with either dietary instrument. IMPLICATIONS: Dietary self-report instruments may be inadequate for analytic epidemiologic studies of dietary fat and disease risk because of measurement error biases.

Relationship of cigarette smoking and radiation exposure to cancer mortality in Hiroshima and Nagasaki.

Cancer mortality among 40,498 Hiroshima and Nagasaki residents was examined in relation to cigarette smoking habits and estimated atomic bomb radiation exposure level. Relative risk (RR) models that are either multiplicative or additive in the two exposures were emphasized. Most analyses were directed toward all nonhematologic (ANH) cancer, stomach cancer, lung cancer, or digestive tract cancer other than stomach cancer, for which there were, respectively, 1,725, 658, 281, and 338 deaths in the follow-up period for this study. Persons heavily exposed to both cigarette smoke and radiation were found to have significantly lower cancer mortality than multiplicative RR models would suggest for ANH cancer, stomach cancer, and digestive tract cancer other than stomach cancer. Surprisingly, the RR function appeared not only to be submultiplicative for some of these cancer site categories but also may be subadditive. The lung cancer RR function could not be distinguished from either a multiplicative or an additive form. The number of deaths was sufficient to permit some more detailed study of ANH cancer mortality: RR functions appeared to be consistent between males and females, though a paucity of heavy smoking females limits the precision of this comparison. The submultiplicative nature of the RR function mentioned above was particularly pronounced among persons who were relatively young (less than or equal to 30 yr of age) at the time of radiation exposure. The RR function for these younger subjects depends strongly on both radiation and cigarette smoke exposure levels. Even light smoking (approximately 5 cigarettes/day) for an extended period of time was associated with a large estimated RR. Implications of these findings are discussed in relation to human carcinogenesis models. As a byproduct, cancer mortality of several sites is significantly related to radiation exposure in this population, after accommodation for the possible confounding effects of cigarette smoking.

Aspects of the rationale for the Women's Health Trial.

A 5.5-fold range in breast cancer incidence rates in 21 countries shows strong correlation with national estimates of per capita intake of dietary fat, but not with other caloric sources (proteins and carbohydrates). It is argued that certain breast cancer and hormone factors may contribute little to the explanation of such international variations in incidence of this neoplasm. It is further argued that experimental studies in animals support a specific role for dietary fat in the promotion of mammary tumors, but the effects of calories alone seem to be largely restricted to tumor initiation. Finally, data from international, migrant-population, and analytic epidemiologic investigations are used to motivate the basic relative risk assumption of study designs thus far proposed for the Women's Health Trial, and some continuing motivations for a dietary intervention (low-fat diet) trial are discussed.

Higher Dimensional Clayton-Oakes Models for Multivariate Failure Time Data.

The Clayton-Oakes bivariate failure time model is extended to dimensions m > 2 in a manner that allows unspecified marginal survivor functions for all dimensions less than m. Special cases that allow unspecified marginal survivor functions of dimension q with q < m, while making some provisions for dependencies of dimension greater than q, are also described.

On the epidemiology of oral contraceptives and disease.

PIP: Adverse and beneficial effects, especially with regard to mortality rates, of oral contraceptives (OC) are reviewed. In 1980 approximately 80 million women used OCs worldwide. OCs were first marketed in the United States in the 1960's, but by the 1980's low-dose combination pills with less estrogen and progesterone content became widespread along with the minipill, injectable preparations depo- medroxyprogesterone DMPA, and norethindrone containing capsules. Relative disease risk estimates are based on cohort studies and case- control studies. The Royal College of General Practitioners RCGP Oral Contraceptive Study of 1974 involved 46,000 women aged over 15 (50% were OC users, 50% were nonusers) the Oxford Family Planning Association Contraceptive Study of 1976 recruited 17,032 women aged 25-39, 56% of whom used OCs, and the Walnut Creek Contraceptive Drug Study of 1981 studied 16,638 women aged 18-54 of whom 28% were OC users and 33% were former users. A somewhat elevated mortality among ever-users of OCs in the order of 20% seems to be indicated by these studies mostly attributable to diseases of the circulatory system. Current OC use is also a risk factor in thrombotic stroke of the order of 4 or 5, but former use of OCs lowers the risk to 2. The effect of OC dose and formulation, duration of use, and predisposing factors on hemorrhagic and thrombotic stroke appears to be inconclusive with varying data from different studies. There is evidence for some increase in ischemic heart disease among current OC users, and also a 2-fold increase of myocardial infarction (MI) when smoking, serum cholesterol, and hypertension is taken into account, moreover higher estrogen dosage also contributes to a higher incidence of MI. There is also a 5-fold increase of venous thromboembolism among OC users induced by duration of use and estrogen potency, as OCs seem to promote atherogenesis, although the roles of progesterone and estrogen are conflicting. combination pills reduce the rate of endometrial cancer, provided protection against ovarian cancer, and do not seem to increase breast cancer incidence, although the relative risk of cervical cancer is elevated. Mortality risks with older OCs outweigh the benefits.^ieng

Results of a randomized feasibility study of a low-fat diet.

A 2-year randomized clinical trial was conducted to test whether free-living women aged 45 to 69 years can reduce the fat content of their diet from the typical US level of approximately 39% to 20% of energy from fat, using readily available foods, when given nutritional and behavioral counseling and social support. Three clinical units randomized 303 selected volunteers into intervention (low-fat eating plan) or control (customary diet) groups. The two groups were comparable at baseline. The intervention group received nutrition instruction and behavioral counseling largely in permanent groups of 12 to 15 participants meeting weekly, then biweekly, and finally monthly. At 6 months, they had substantially reduced the mean proportion of total energy from fat from 39.1% to 20.9%, compared with the control group's nonsignificant reduction from 39.0% to 38.1%. At 12 and 24 months, they sustained the reduction of energy from fat. Weight loss and plasma cholesterol level changes in the intervention group supported the self-recorded dietary intake changes. Attendance at intervention sessions averaged 75% during the first 6 months and, subsequently, 60% to 70%. Four-day food records for the randomized women were obtained at 6 and 12 months from approximately 95% and at 24 months from 87%. A clinical trial of a low-fat diet is feasible in women.

Purification of two allergens from Dermatophagoides pteronyssinus using monoclonal antibodies.

Fractionation of soluble extracts from the house dust mite Dermatophagoides pteronyssinus (DP) by SDS-PAGE and crossed immunoelectrophoresis (CIE) revealed at least fifty distinct protein components. Western blotting and crossed radioimmunoelectrophoresis (CRIE) indicated that fewer than one quarter of these components were allergens as determined by their ability to bind IgE from allergic individuals. Following immunization with a crude extract, two monoclonal antibodies were raised against distinct components which exhibited IgE binding capacities in Western blot and CRIE. Affinity chromatography using these monoclonal antibodies yielded components which elicited positive skin test reactions in patients allergic to DP.

Rearrangements of T-cell receptor beta-chain genes in human leukaemias.

Rearrangements of the T-cell receptor (TCR), beta-chain genes and immunoglobulin (Ig) heavy chain genes in several T-cell leukaemias (T-ALL and ATL), and some B-cell and myelogenous leukaemias were investigated. Two out of 15 cases of T-cell leukaemia tested failed to show a rearrangement pattern of TCR beta genes although both expressed mRNA for this gene. The remaining 13 cases showed diverse patterns of rearrangements involving either C beta 1, C beta 2 or both. C beta 1 but not C beta 2 was deleted in some of the T-cell leukaemias. Polyclonal T cells from four normal individuals showed the germ line pattern and an additional two bands in Hind III digested DNA. Except for one, all cases of C-ALL (B-cell leukaemia) showed a rearranged JH locus which was not evident in any of T-cell leukaemias studied. One case of B-cell leukaemia showed a rearrangement of both TCR beta genes and JH genes. The results of these studies suggest that rearrangement of TCR and Ig genes occurs at a very early stage of differentiation of stem cells and does not appear to play a direct role in leukaemogenesis per se.

Maintenance of a low-fat diet: follow-up of the Women's Health Trial.

This report examines the maintenance of a low-fat diet 1 year on average after the completion of intervention sessions among participants in the Women's Health Trial (WHT). The WHT was a randomized controlled trial of the feasibility of adoption of a low-fat diet among women of moderate or increased risk of breast cancer, conduced in Seattle, Houston, and Cincinnati in 1985-1988. The women randomized to the low-fat diet attended an intensive dietary intervention program for 5-37 months. Intervention women were highly successful in reducing their dietary fat intake from 40.0% of energy intake at baseline to 26.3% by the end of the trial, based on a food frequency questionnaire (or an estimated 24% adjusted for the inaccuracies of a food frequency questionnaire versus a 4-day diet record). During 1989, 1 year on average after the WHT ended, 448 intervention women and 457 control women (87% of eligibles) completed a follow-up survey to determine the degree of maintenance of the diet. The intervention women maintained the low-fat diet with an increase of only 1.4 percentage points of energy from fat, despite the fact that they had attended no further intervention sessions and had made no commitment to maintain the diet beyond the end of the WHT. Furthermore, the degree of maintenance of the low-fat diet was not dependent on the length of time in the intervention, which suggests that intervention led to a sustained change in eating habits after as little as 5-9 months (8-13 classes).(ABSTRACT TRUNCATED AT 250 WORDS)

Potentiation of hybridoma production by the use of mouse fibroblast conditioned media.

L-CM is a conditioned medium prepared from cultures of L-929 cells, a murine fibroblast line. It will promote the growth and antibody secretion of B cell hybridomas after fusion as well as facilitating cloning at limit dilution and the growth of cloned B cell lines in bulk culture. The medium is easy to prepare and stores well at 4 degrees C. It thus provides a convenient alternative to the use of feeder cells in the production of monoclonal antibodies.

Varicella-zoster virus infection after marrow transplantation for aplastic anemia or leukemia.

Nearly one-half of marrow transplant recipients who survive at least 6 months develop varicella-zoster virus (VZV) infection. Of 92 cases studied, 82 occurred within the first 12 months after transplant. Only one patient had recurrent infection. Seventy-seven patients had herpes zoster, 22 with subsequent cutaneous dissemination, and 15 had varicella. The overall mortality rate was 8%, and all deaths occurred within 9 months of transplant. Twenty-six of 32 patients studied had significant rises in VZV antibody during recovery. Among patients with acute leukemia, those with syngeneic transplants had a significantly lower incidence of VZV infection than those with allogeneic transplants. Incidence was slightly, but not significantly, decreased among patients with aplastic anemia. In contrast to other infections, the incidence of VZV infection was not influenced by graft-versus-host disease or predicted by the results of dinitrochlorobenzene skin testing.

Relative risk regression analysis of epidemiologic data.

Relative risk regression methods are described. These methods provide a unified approach to a range of data analysis problems in environmental risk assessment and in the study of disease risk factors more generally. Relative risk regression methods are most readily viewed as an outgrowth of Cox's regression and life model. They can also be viewed as a regression generalization of more classical epidemiologic procedures, such as that due to Mantel and Haenszel. In the context of an epidemiologic cohort study, relative risk regression methods extend conventional survival data methods and binary response (e.g., logistic) regression models by taking explicit account of the time to disease occurrence while allowing arbitrary baseline disease rates, general censorship, and time-varying risk factors. This latter feature is particularly relevant to many environmental risk assessment problems wherein one wishes to relate disease rates at a particular point in time to aspects of a preceding risk factor history. Relative risk regression methods also adapt readily to time-matched case-control studies and to certain less standard designs. The uses of relative risk regression methods are illustrated and the state of development of these procedures is discussed. It is argued that asymptotic partial likelihood estimation techniques are now well developed in the important special case in which the disease rates of interest have interpretations as counting process intensity functions. Estimation of relative risks processes corresponding to disease rates falling outside this class has, however, received limited attention. The general area of relative risk regression model criticism has, as yet, not been thoroughly studied, though a number of statistical groups are studying such features as tests of fit, residuals, diagnostics and graphical procedures. Most such studies have been restricted to exponential form relative risks as have simulation studies of relative risk estimation procedures with moderate numbers of disease events.

Methodologic research needs in environmental epidemiology: data analysis.

A brief review is given of data analysis methods for the identification and quantification of associations between environmental exposures and health events of interest. Data analysis methods are outlined for each of the study designs mentioned, with an emphasis on topics in need of further research. Particularly noted are the need for improved methods for accommodating exposure assessment measurement errors in analytic epidemiologic studies and for improved methods for the conduct and analysis of aggregate data (ecologic) studies.