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Biomedical subjects

D O Dixon

Publications and source records attributed to D O Dixon.

18 recordsLinked to original sources
PubMed1992

Bayesian subset analysis in a colorectal cancer clinical trial.

Subset analysis is the examination of treatment comparisons within groups of patients with restricted levels of patient characteristics. Such analyses are vulnerable to multiplicity effects. We examine the problem in the context of a proportional hazards model with terms for treatment, each of several dichotomous covariates representing the patient characteristics of interest, and treatment-by-covariate interaction effects. Parametrically, a subset-specific treatment effect is equal to the treatment effect term plus a linear combination of the interaction terms. We present Bayesian point and interval estimates under the assumption that the interaction terms are exchangeable and the prior distributions for the other regression parameters are locally uniform. This produces a shrinking of the estimated interaction effects towards zero, thereby discounting them and dealing in a natural way with multiplicity. We illustrate the method using results of a recent North Central Cancer Treatment Group/Mayo Clinic study in advanced colorectal cancer.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1992

k-ratio t tests for multiple comparisons involving several treatments and a control.

We consider the problem of simultaneously comparing several treatment means with a control mean and also with one another. Following an elementary decision-theoretic Bayesian approach requiring the choice of a type-I to type-II error-seriousness ratio k, a posteriori t tests are derived for testing both treatment versus control (TvC) and treatment versus treatment (TvT) differences. These k-ratio t tests are strictly comparisonwise in nature. That is, the test applied to any TvC or TvT difference d, depends in no way at all on whether the other differences are being tested. The test for d, however, does depend on the sizes of the other differences through tG, the standardized average of the observed TvC differences, and through FT, the observed between-treatments F ratio. From these adaptive dependences on tG and FT, the critical t values can be large or small, thus avoiding the intuitive objections of under- or over-conservatism in classical comparisonwise or experimentwise level testing rules.

Bayes Theorem↗
PubMed1992

Therapy of relapsed or refractory low-grade follicular lymphomas: factors associated with complete remission, survival and time to treatment failure.

Patients with relapsed low-grade follicular lymphomas (LGFL) frequently respond to subsequent therapy and can have long survival, but are rarely cured. Factors associated with complete remission (CR) rate, length of survival, and time to treatment failure (TTF) after relapse are not well known. We assessed such factors by multivariate analysis in a retrospective review of 95 patients with relapsed LGFL treated with investigational chemotherapy regimens at our institution. The CR rate after therapy was 22%; the likelihood of achieving CR was inversely associated with the number of previous treatment failures (P less than 0.001) and serum LDH level (P less than 0.05). Both the presence of constitutional symptoms and a history of more than two previous treatment failures were associated with shortened survival and TTF. Hemoglobin level was also significantly associated with survival. Prognostic models for survival and TTF were derived to define patient groups with different projected outcomes after therapy for relapsed disease. The results of this study can be used to select patients for new investigational treatments and to evaluate the outcome of such therapies.

Adult↗
PubMed1991

Bayesian subset analysis.

As a means of assessing the importance of variation in treatment effect among patient subsets, we derived posterior distributions for subset-specific treatment effects. The effects are represented by combinations of terms for treatment and treatment-by-covariate interaction effects in familiar regression models. Exchange-ability among the interactions is a key assumption; thus, the results are of interest primarily in the context of examining a collection of subsets with no definite a priori distinction relative to treatment effect. Exchangeability leads to a shrinking of the posterior distributions of the interaction terms toward the natural origin of 0, offsetting the tendency of the estimated effects to disperse. The method is applied to parameter estimates from a proportional hazards regression analysis of survival data from a clinical trial, invoking the approximate multivariate normal distribution of the estimates. No subjective prior distributions are required. Vague priors are used for all of the regression coefficients except the treatment-by-covariate interactions, which are assumed to follow a normal distribution.

Clinical Trials as Topic↗
PubMed1990

Autologous bone marrow transplantation in multiple myeloma: identification of prognostic factors.

Multiple myeloma remains a universally fatal malignancy with a median survival time not exceeding 3 years. A clinical trial was undertaken to determine feasibility and efficacy of marrow-ablative chemoradiotherapy supported by unpurged autologous bone marrow (ABMT) and to define prognostic variables. Total body irradiation and either melphalan or thiotepa were administered to 55 patients (median age 53 years; range 20 to 66 years). The group of 21 patients with resistance to standard melphalan-prednisone and to continuous infusions of vincristine and Adriamycin with high dose dexamethasone (VAD) included 7 with primary unresponsive disease and 14 with resistant relapse; among the 34 patients achieving remission with the VAD regimen, 14 were in first and 20 in a subsequent remission. Marked cytoreduction by greater than or equal to 75% was observed among all 21 patients with refractory myeloma, whereas further cytoreduction of this magnitude was noted in only 56% of the 34 patients already in remission after VAD. Five of the 6 early deaths among all 55 patients occurred in the 14 patients with resistant relapse, none of whom achieved complete remission and who, as a group, had median durations of relapse-free and overall survival of only 8 and 7 months, respectively. Among the 41 remaining patients, there was only one early death, and 27% achieved complete remission including a 36% incidence among the 14 patients treated in first remission; their projected 4-year survival rate was 82% regardless of their disease status (first or later remission or primary resistance). When information about sensitivity to prior therapy is unavailable, the presence before ABMT of both high beta-2-microglobulin levels (greater than 3 mg/L) and non-IgG isotype helped identify 9 among the 55 patients with a very poor prognosis: all 8 responders relapsed within 9 months, and 8 patients died within 15 months. By contrast, a 4-year projected survival rate of over 70% for the other patients (about 80% of this series) justifies further investigation of this novel treatment approach in comparison with standard dose regimens. Our results indicate that marrow-ablative therapy cannot be recommended for myeloma patients with resistant relapse or those with a combination of risk factors (advanced tumor burden, absence of IgG isotype). The apparent lack of an adverse effect of even marked plasmacytosis in autografts (up to 30%) emphasizes the need for better cytoreduction rather than bone marrow purging.

Adult↗
PubMed1990

High-dose melphalan and granulocyte-macrophage colony-stimulating factor for refractory multiple myeloma.

High-dose melphalan has induced remissions in about 40% of patients with refractory myeloma, but the mortality has been high, at about 20%, due to complications of prolonged granulocytopenia. In an attempt to stimulate earlier granulocyte recovery, recombinant human granulocyte-macrophage colony-stimulating factor (GM-CSF) was administered subcutaneously to 23 patients with refractory myeloma who had been treated with melphalan at a high dose of 100 mg/m2. Thirty-nine percent of patients achieved marked tumor cytoreduction by at least 75%, 2 died within 2 months from infectious complications during severe neutropenia; and median durations of relapse-free and overall survival were 7 and 10+ months, respectively. The nine patients presenting with both advanced age over 50 years and a long history of prior therapy of over 1 year required significantly longer median times of 31 days for granulocytes and of 63 days for platelets to reach safe levels of at least 500/microL and 50,000/microL, respectively, than the 14 remaining patients who had none or only one of these adverse features (21 and 26 days, respectively). In a historic control of 43 patients treated previously with high-dose melphalan but without GM-CSF, hematologic recovery to the aforementioned levels of granulocytes and platelets proceeded over almost 5 weeks, regardless of age and prior treatment exposure. Thus GM-CSF seems to hasten marrow recovery, especially in patients with adequate normal marrow stem-cell reserve as defined by younger age or less prior therapy. While not shortening the duration of neutropenia, GM-CSF dose increments (from 0.25 to 0.5 to 0.75 mg/m2) increased the incidence of severe toxicity from 0% to almost 40%, especially among older patients. These results support the usefulness of low-dose GM-CSF (0.25 mg/m2) in stimulating marrow recovery in selected patients with adequate marrow reserve treated with high-dose melphalan for refractory multiple myeloma.

Colony-Stimulating Factors↗
PubMed1990

Bronchial micronuclei as a marker of an early stage of carcinogenesis in the human tracheobronchial epithelium.

In the bronchial epithelium, smoking initiates a multistep process that first appears histologically as premalignant squamous metaplasia/dysplasia, a biological predecessor of squamous-cell lung cancer. Reflecting chromosomal damage from a carcinogenic insult, micronuclei may reveal earlier events in the carcinogenic sequence. We prospectively evaluated and correlated micronucleus count, histology (index of metaplasia) and smoking exposure in 35 consecutive subjects (9 active smokers, 10 previous smokers and 16 never-smokers) undergoing diagnostic bronchoscopy. Samples for micronuclei and histological evaluation were taken from the main carinal mucosa in each subject for site-specific comparisons. The median and mean micronucleus counts per 1,000 cells were significantly higher in active smokers than in non-smokers (subjects who had never smoked and previous smokers): median counts were 3.7 vs. 1.4, p = 0.03; mean counts were 4.7 vs. 1.9, p = 0.01. There was no significant difference, however, in micronucleus counts between subjects who had never smoked and previous smokers. Bronchial metaplasia and smoking history were not associated. Our findings suggest that micronuclei are a readily quantitated, early intermediate-endpoint marker for detecting tobacco-initiated tracheobronchial carcinogenesis.

Adult↗
PubMed1990

Prognostic factors and clinical trials.

The identification of prognostic factors is an important area of cancer research. This article contains an introduction to the uses of prognostic factors, statistical methods for their identification, and a summary of the literature concerning the evolution of serum beta 2 microglobulin as a prognostic factor in multiple myeloma.

Biomarkers, Tumor↗
PubMed1989

Direct estimation of latent time for radiation injury in late-responding normal tissues: gut, lung, and spinal cord.

Mixture models are proposed for simultaneous analysis of the latency and fractionation characteristics of radiation injury in late-responding normal tissues. The method is an extension of the direct analysis for quantal response data. Conceptually, the application of the mixture model is based on the biological observation that over a wide range of doses a proportion of the irradiated subjects will never express damage. Mixture models allow the time of occurrence to be utilized in the analysis. Furthermore, this type of model takes time-censored observations into account in a natural way and provides an adequate framework for modelling and analysis of effect-dependent latency. Mixture models with complete and incomplete repair are applied to dose-incidence data for four late endpoints in rodents: death from radiation-induced pneumonitis, leg paralysis after spinal-cord irradiation, and radiation-induced rectal stenosis and anal discharge. Radiation-induced pneumonitis had an effect-dependent latency. The modelling of this phenomenon correlates well with the results of histologic studies. Interestingly, the ratio of hazard rates was not constant for this endpoint. The dominating feature in the latency of radiation injury to the spinal cord was a strong dependency on dose per fraction. After correction for this effect a tendency towards a longer latent time for lower effect levels was observed. For the rectal complications, there was no difference between latency with radiation only vs. radiation combined with cis-platin.

Animals↗
PubMed1989

Analysis of risk factors for fatal hemorrhage during induction therapy of patients with acute promyelocytic leukemia.

Acute promyelocytic leukemia (APL), an uncommon subtype of acute myelogenous leukemia (AML), has a high incidence of early hemorrhagic death during induction therapy; however, patients with APL surviving induction and obtaining complete remission have a good prognosis, with a longer remission duration than other subtypes of AML. We sought to determine if changes in selected clinical and laboratory coagulation parameters during induction therapy were significantly associated with fatal hemorrhage in that week, or were predictive of fatal hemorrhage in the following week. The first six weeks of induction therapy were studied in 65 patients, during which time 23 patients (35%) died from hemorrhagic complications. Time intervals analyzed were week 1, week 2, weeks 3 and 4, and weeks 5 and 6. There was no significant difference in the prevalence of severe hypofibrinogenemia (less than 150 mg%), prolongation of the prothrombin time (greater than 14 s), or presence of infection between patients who sustained fatal hemorrhage versus those who did not, for any given time period. The most significant parameter was the inability to obtain a posttransfusion platelet count of over 40,000/microliters in at least one half of the platelet transfusions administered in that week (p less than 0.001). This last parameter was the only variable that was also significantly associated with an increased risk of fatal hemorrhage for the following week (p less than 0.005). Clinical trials investigating management of coagulopathy in APL should evaluate the effect of therapy on response to platelet transfusion as well as on other laboratory parameters.

Adolescent↗
PubMed1979

The caries-preventive effect of amine fluorides and inorganic fluorides in a mouthrinse or dentifrice after 30 months of use.

The study groups using a dentifrice and mouthrinse both containing fluorides, a dentifrice containing stannous fluoride and a mouthrinse containing sodium fluoride, or a mouthrinse containing sodium fluoride with a placebo dentifrice had a 20.7% to 29.0% lower DMF increment than the control group after 30 months. These differences were significant. The study groups using a dentifrice containing amine fluorides and a placebo mouthrinse, a mouthrinse containing amine fluorides and a placebo dentifrice, or a dentifrice containing stannous fluoride and a placebo mouthrinse had a 13.6% to 22.4% lower DMF increment than the control group. These differences were not statistically significant. There was no significant difference in effectiveness against caries between the use of the organic or inorganic fluoride products.

Amines↗
PubMed1978

The reproducibility and interpretation of carbon dioxide cystometry.

The day-to-day and same-day variability of carbon dioxide cystometry was examined in a population of men. Considerable variability was observed in each parameter monitored. The implications of such variability, and the validity and significance of certain cystometric events are discussed.

Adult↗
PubMed1977

Comparison of gingival health and gingival crevicular fluid flow in children with and without diabetes.

GCF flow measurements and a clinical scoring of gingival health were both recorded for a group of 56 children with diabetes and 41 children without diabets. The children with diabetes had significantly more gingival disease than the children without diabetes when compared with either measure. A small but significant correlation was found between the GCF flow and the clinical scores with the children with diabetes but not with the children without diabetes.

Adolescent↗