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At least 1,513 records · Page 84Linked to original sources
PubMed2004

Improving the efficiency of nested case-control studies of interaction by selecting controls using counter matching on exposure.

BACKGROUND: Studies of the effect of exposure to a risk factor measured in an entire cohort may be augmented by nested case-control subsets to investigate confounding or effect modification by additional factors not practically assessed on all cohort members. We compared three control-selection strategies-matching on exposure, counter matching on exposure, and random sampling-to determine which was most efficient in a situation where exposure is a known, continuous variable and high doses are rare. METHODS: We estimated the power to detect interaction using four control-to-case ratios (1:1, 2:1, 4:1, and 8:1) in a planned case-control study of the joint effect of atomic bomb radiation exposure and serum oestradiol levels on breast cancer. Radiation dose is measured in the entire cohort, but because neither serum oestradiol level nor the true degree of interaction was known, we simulated values of oestradiol and hypothetical levels of oestradiol-radiation interaction. RESULTS: Compared with random sampling, power to detect interaction was similarly higher with either matching or counter matching with two or more controls. CONCLUSIONS: Because counter matching is generally at least as efficient as random sampling, whereas matching on exposure can result in loss of efficiency and precludes estimation of exposure risk, we recommend counter matching for selecting controls in nested case-control studies of the joint effects of multiple risk factors when one is previously measured in the full cohort.

Breast Neoplasms↗
PubMed2005

CGMIM: automated text-mining of Online Mendelian Inheritance in Man (OMIM) to identify genetically-associated cancers and candidate genes.

BACKGROUND: Online Mendelian Inheritance in Man (OMIM) is a computerized database of information about genes and heritable traits in human populations, based on information reported in the scientific literature. Our objective was to establish an automated text-mining system for OMIM that will identify genetically-related cancers and cancer-related genes. We developed the computer program CGMIM to search for entries in OMIM that are related to one or more cancer types. We performed manual searches of OMIM to verify the program results. RESULTS: In the OMIM database on September 30, 2004, CGMIM identified 1943 genes related to cancer. BRCA2 (OMIM *164757), BRAF (OMIM *164757) and CDKN2A (OMIM *600160) were each related to 14 types of cancer. There were 45 genes related to cancer of the esophagus, 121 genes related to cancer of the stomach, and 21 genes related to both. Analysis of CGMIM results indicate that fewer than three gene entries in OMIM should mention both, and the more than seven-fold discrepancy suggests cancers of the esophagus and stomach are more genetically related than current literature suggests. CONCLUSION: CGMIM identifies genetically-related cancers and cancer-related genes. In several ways, cancers with shared genetic etiology are anticipated to lead to further etiologic hypotheses and advances regarding environmental agents. CGMIM results are posted monthly and the source code can be obtained free of charge from the BC Cancer Research Centre website http://www.bccrc.ca/ccr/CGMIM

Algorithms↗
PubMedDate not supplied

A survival predictive model in patients undergoing radical resection of ampullary adenocarcinoma.

BACKGROUND/AIMS: Radical resection with either pancreaticoduodenectomy or pylorus-preserving pancreaticoduodenectomy is considered to be the standard treatment for most ampullary carcinomas, but the prognostic predictive model has not yet been developed. METHODOLOGY: The pretreatment, treatment, and follow-up variables of data of 47 patients undergoing radical resection for the ampullary carcinoma were analyzed to determine the favorable prognostic variables. Employing the Kaplan-Meier method, the cumulative survival rates of the ampullary carcinoma were calculated. By Cox regression model, a stepwise multivariate analysis was performed to analyze the contributing factors of the survival rate, and a predictive survival equation was obtained. RESULTS: With the results of the univariate analysis, the variables significantly associated with favorable prognosis were younger age (<63 years), TNM stage (stage I or II or III), and the degree of tumor differentiation (well or moderately differentiated). When the above three variables were examined as covariates by Cox regression in multivariate analysis, the TNM stage and the degree of tumor differentiation were independently correlated with the survival. A predictive survival equation obtained with the beta-coefficients of the above three variables was as follows: S (t) = [So (t)] P, P = exp (0.0234 x age - 1.8744 x tumor differentiation + 1.1576 x TNM stage) CONCLUSIONS: This predictive survival equation can predict the survival and the favorable outcome of patients treated with radical resection of ampullary carcinoma.

Actuarial Analysis↗
PubMed2006

Randomised and non-randomised prospective controlled cohort studies in matched-pair design for the long-term therapy of breast cancer patients with a mistletoe preparation (Iscador): a re-analysis.

OBJECTIVE: Expanded presentation and re-analysis of previously published data of randomized and non-randomized studies on mistletoe therapy with breast cancer patients [3, 4]. The main question is: Does a re-analysis confirm the previously reported effects of prolonging the survival of patients with breast cancer under long-term application of a complementary/anthroposophic therapy with the European mistletoe preparation Iscador? DATA SOURCES: (1) Randomised matched-pairs study: Breast cancer patients with only lymphatic metastases (17 pairs) that had never used mistletoe therapy were matched for several prognostic factors. By paired random allocation, one patient of a pair received a suggestion of mistletoe therapy to be applied by the attending physician. (2) Non-randomised matched-pairs studies: Patients that had already received mistletoe (Iscador) therapy were matched to control patients from the same pool using the same prognostic criteria. Three groups were recruited by this procedure: breast cancer with local recurrences and no metastases (42 pairs), breast cancer with only lymphatic metastases (55 pairs), and breast cancer with distant metastases (83 pairs). ANALYSIS: Cox proportional hazard models and sensitivity analyses based on subsets of the original data sets according to strict or lose application of the matching criteria. RESULTS: The results of this re-analysis are consistent with the earlier results, even when comparing different methods and subsets. In the randomised study, the effect of long-term Iscador therapy on overall survival is significantly in favour of the Iscador therapy: Estimate of the median difference and 95 % confidence interval in years 2.5 (0.83, 4.50). The results for the non-randomised studies were also in favour of the Iscador therapy: Breast cancer with local recurrences and no metastases: estimate of hazard ratio and 95 % confidence interval 0.52 (0.23, 1.17); breast cancer with lymphatic metastases: 0.27 (0.15, 0.50); breast cancer with distant metastases: 0.53 (0.32, 0.88). As a short-term effect of this therapy, psychosomatic self-regulation noticeably increases within 3 months in the Iscador group in comparison to the control group in the randomised study: estimate of the median difference 0.90 (0, 1.75). CONCLUSION: The re-analysis demonstrates that the effects shown in the previously published data are consistent despite using different analytic methods and different subsets. Overall, the survival of patients receiving mistletoe treatment with Iscador is longer in these studies. In the short term, psychosomatic self-regulation, as a measure of autonomous coping with the disease, rises more under Iscador therapy than under conventional therapy alone.

Adult↗
PubMed1988

[Analysis of the geographic distribution of cancer incidence exemplified by lung tumors in East Germany for the period 1978-1982].

Analysing the regional distribution of cancer incidence a graphic presentation of the data in form of cancer maps often give a clear idea of the underlying distribution. Nevertheless, if the cancer map is variegated, an answer to the question of regional dependence of the incidence is difficult to find. Statistical methods as the test of Kemp et al. (3), which is based on the mean absolute difference in rank between all possible pairs of adjacent regions with a common border, or outlier tests can be helpful in such cases. An easy calculable approximation of Kemp's method will be presented and demonstrated on lung cancer incidence in districts of the GDR over the five-year period 1978-1982. Moreover statistical methods of generating new hypotheses about possible risk factors will be discussed.

Atlases as Topic↗
PubMed1995

Imprecise exposure assessment and the sample size requirements of case-control studies of residential magnetic field exposure and cancer in adults.

A computer program simulating case-control studies is described. It is used to estimate the minimum sample size required and to assess how this is affected by imprecise exposure assessment. In particular, the consequences of neglecting measurements of nonresidential exposure in case-control studies of residentially exposed adults are investigated. According to this model, while the consequent loss of power is not as large as was predicted by algebraic methods, it would be unwise to neglect it when planning a study.

Adult↗
PubMed2004

Multi-class tumor classification by discriminant partial least squares using microarray gene expression data and assessment of classification models.

High-throughput DNA microarray provides an effective approach to the monitoring of expression levels of thousands of genes in a sample simultaneously. One promising application of this technology is the molecular diagnostics of cancer, e.g. to distinguish normal tissue from tumor or to classify tumors into different types or subtypes. One problem arising from the use of microarray data is how to analyze the high-dimensional gene expression data, typically with thousands of variables (genes) and much fewer observations (samples). There is a need to develop reliable classification methods to make full use of microarray data and to evaluate accurately the predictive ability and reliability of such derived models. In this paper, discriminant partial least squares was used to classify the different types of human tumors using four microarray datasets and showed good prediction performance. Four different cross-validation procedures (leave-one-out versus leave-half-out; incomplete versus full) were used to evaluate the classification model. Our results indicate that discriminant partial least squares using leave-half-out cross-validation provides a more realistic estimate of the predictive ability of a classification model, which may be overestimated by some of the cross-validation procedures, and the information obtained from different cross-validation procedures can be used to evaluate the reliability of the classification model.

Algorithms↗
PubMed2006

The MISCAN-Fadia continuous tumor growth model for breast cancer.

The MISCAN-Fadia model was used to analyze the impact of screening and adjuvant treatment on U.S. breast cancer mortality between 1975 and 2000. MISCAN-Fadia uses the concept of "fatal diameter" to model survival and screening benefit and is based on continuous tumor growth. It consists of four major components: population, natural history, screening, and treatment. Population parameters were quantified using U.S. population data. Most natural history and screening parameters were fitted to the Swedish Two County screening trial data; some were based on Surveillance, Epidemiology, and End Results data. Adjuvant treatment parameters were quantified using data from the Early Breast Cancer Trialists' Collaborative Group's meta-analysis. The simulated trend in incidence matches the observed trend reasonably well; the simulated mortality is equal to the observed in 1975 but becomes increasingly too high in 2000. We estimate that screening leads to a 15% and adjuvant treatment to a 21% mortality reduction in the year 2000.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed2003

Reproducibility of the assessment of tumor extent in the breast using multiple image modalities.

The accuracy of breast-conserving therapy (BCT) is limited by uncertainties in the assessment of tumor extent. These uncertainties may result in too wide treatment volumes leading to undesirable cosmetic results, or too narrow treatment volumes leading to higher probabilities of local recurrence. The aim of this study is to quantify the reproducibility of the assessment of tumor extent in the breast at preoperative diagnostic imaging with multiple imaging modalities and at pathology, applied to (1) determining minimum surgical safety margins to reduce the probability of underestimating the tumor extent due to uncertainty in the radiological assessment, and (2) defining the minimum difference between two measurements of tumor size that indicates a significant reduction of tumor extent in response to neoadjuvant chemotherapy or hormonal therapy. Measurements of the largest tumor diameter in mammography, ultrasonography, contrast-enhanced magnetic resonance imaging, and at pathology were retrieved, retrospectively, for 105 patients eligible for BCT. An analysis of variance technique is employed to separate uncertainty at preoperative diagnostic imaging from uncertainty at pathology. The random variations are thus calculated independently of the systematic deviations, avoiding the necessity to choose a gold standard. Moreover, the technique does not require repeat measurements of tumor extent, thus allowing the use of data that is obtained in daily clinical practice, while avoiding bias due to recollection. The magnitude of the random variations is used to determine minimum surgical safety margins and to define the minimum significant difference between two measurements of tumor size. The overall random variations in the assessment of tumor extent are on the order of 3 mm (1 s.d.) with only little differences of about 0.3 mm between the four techniques. The dependence of the random variations on tumor size was found significant (p < 0.05) for mammography (2.7 mm vs 4.2 mm, 1 s.d.) and ultrasonography (2.5 mm vs 3.8 mm, 1 s.d.) for tumors up to 17 mm compared to those that are larger. A minimum surgical safety margin on the order of 5 mm for tumors up to 17 mm and 7 mm for larger tumors takes the uncertainty in radiological assessment of the tumor extent into account effectively in 95% of the performed surgical procedures. A minimum difference in largest tumor diameter of 7 mm for tumors up to 17 mm and 9 mm for those that are larger indicates a significant (p < 0.05) reduction of tumor extent in response to neoadjuvant chemotherapy or hormonal therapy. The reproducibility of the assessment of tumor extent at preoperative diagnostic imaging is of comparable magnitude to the reproducibility at pathology. The uncertainty in the preoperative assessment of tumor extent constitutes a large portion (5-7 mm) of the current safety margin in breast-conserving surgery (10 mm). In monitoring response to neoadjuvant chemotherapy or hormonal therapy using repeat imaging before and after treatment, the current clinical guidelines may produce approximately 10% false-positive responses for tumors between 20 and 30 mm.

Adult↗
PubMed2006

Computer-aided detection of breast cancer: a cost-effectiveness study.

PURPOSE: To analyze the cost-effectiveness of adding computer-aided detection (CAD) to a screening mammography program. MATERIALS AND METHODS: A Markov model was developed to compare three hypothetical groups of women aged 40-79 years. The first group was composed of women undergoing mammographic screening without CAD; the second, of women undergoing mammographic screening with CAD; and the third, of women undergoing observation without screening. Cost-effectiveness was expressed as the marginal cost per year of life saved (MCYLS). MCYLS was calculated for screening mammography with CAD compared with screening mammography alone and for screening mammography alone compared with observation. Sensitivity analyses were performed by varying the cost of CAD, the rates of cancer detection with CAD, and the stage distribution of breast cancers diagnosed with CAD. RESULTS: Adding CAD to a mammographic screening program resulted in a MCYLS of $19,058. The MCYLS of screening mammography alone compared with observation was $16,023. CAD increases the marginal effectiveness of screening by 29%; however, the marginal cost of screening is also increased by 34%. Varying the cost of CAD yields a linear increase in MCYLS from $8937 with CAD at $9 per case to $24,924 with CAD at $25 per case. The cost-effectiveness of CAD is dependent on the magnitude of the increase in cancer detection rates with CAD but is also affected by the stage distribution of cancers diagnosed with CAD. CONCLUSION: The MCYLS is 19% greater for CAD added to screening versus screening mammography alone but is still within the accepted range for cost-effectiveness.

Adult↗