Biomedical subjects

D F Heitjan

Publications and source records attributed to D F Heitjan.

60 records · Page 4Linked to original sources

PubMedDate not supplied

Problems with interval estimates of the incremental cost-effectiveness ratio.

The defining feature of a confidence interval is that it has a fixed minimum probability of covering the true value of the parameter being estimated, whatever the value of the parameter. The authors demonstrate by simulation that some recently proposed methods for interval estimation of the incremental cost-effectiveness ratio (ICER) either do not satisfy this definition or have other problems that limit their usefulness in applications. The problems are most prominent when the ICER is large and the true effectiveness difference is small relative to its standard error. A modification of the percentile bootstrap confidence interval that involves a reordering of the sample space provides a partial solution of the problem.

Confidence Intervals↗

PubMedDate not supplied

Prevention with tamoxifen or other hormones versus prophylactic surgery in BRCA1/2-positive women: a decision analysis.

PURPOSE: Recent randomized controlled trials have shown that tamoxifen and raloxifene may prevent invasive breast cancer. This decision analysis study compares the outcomes of chemoprevention with tamoxifen, raloxifene, or oral contraceptives with the outcomes of prophylactic surgery among women with high-risk BRCA1/2 mutations. PATIENTS AND METHODS: We used a simulated cohort of 30-year-old women who tested positive for BRCA1/2 mutations and constructed a Markov model with Monte Carlo simulations, incorporating cumulative breast and ovarian cancer incidence rates from the literature and survival figures from SEER data. We assumed that prophylactic surgery reduces ovarian cancer risk by 45% and breast cancer risk by 90%, that tamoxifen reduces invasive breast cancer risk by 49%, and that raloxifene has similar efficacy and safety in premenopausal and postmenopausal women. We used data obtained from high-risk women by a time trade-off questionnaire to calculate quality-adjusted life-years. We based our cost estimates for hospital and ambulatory care on Health Care Financing Administration payments, the SEER-HCFA database, and the Pharmacy Fundamental Reference. RESULTS: In our model, a 30-year-old BRCA1/2+ woman could prolong survival by 0.9 years (95% probability interval, 0.4-1.2 years) by having bilateral oophorectomy, 3.4 years (2.7-3.7 years) by having bilateral mastectomy, and 4.3 years (3.6-4.6 years) by having both procedures instead of surveillance alone. Chemoprevention with tamoxifen and raloxifene increased survival by 1.6 years (1.0-2.1 years) and 2.2 years (1.3-2.8 years), respectively. Chemoprevention yielded more quality-adjusted life-years than did prophylactic surgery, even when treatment was delayed to age 40 or 50 years. All these procedures were cost-effective or cost-saving compared with surveillance alone. DISCUSSION: Our model suggests that although surgery may yield more substantial survival and cost benefits, quality of life issues may make chemoprevention a more attractive option for young women at high genetic risk.

Adult↗

PubMedDate not supplied

Decision analysis of tamoxifen for the prevention of invasive breast cancer.

PURPOSE: The recent Breast Cancer Prevention Trial has shown that tamoxifen may prevent invasive breast cancer. We used a Markov model to estimate the long-term effects of chemoprevention with tamoxifen on survival, quality-adjusted survival, and health care costs. METHODS: We used a hypothetical cohort of women with breast-cancer risk similar to that of participants in the Breast Cancer Prevention Trial, and a computer-based decision analysis (Markov model and 500 Monte Carlo simulations) to model the outcomes of interest. Survival calculations were from Surveillance, Epidemiology, and End-Results (SEER) data; preference ratings from a time trade-off questionnaire administered to a group of average-risk women; and cost estimates from the Group Health Cooperative of Puget Sound and the Health Care Financing Administration. We obtained utility measures for quality-adjustment by administering a time trade-off questionnaire to a group of community-based women. RESULTS: Use of tamoxifen prolonged the average survival of cohort members by 69 days (95% probability interval [PI] 27 to 117) for those who started use at age 35 years; 40 days (95% PI 16 to 67) for those who started use at age 50 years; and 27 days (95% PI 14 to 40) for those who started use at age 60 years. Tamoxifen extended quality-adjusted survival by 38 days (95% PI 0.1 to 82) at age 35, 25 days (95% PI 0 to 50) at age 50, and 22 days (95% PI 5 to 39) days at age 60. Chemoprevention with tamoxifen cost $46,619 (95% PI $27,928 to $98,796) per life year life saved for women who started at age 35; for women over age 50, it cost more than $50,000 per life year saved. DISCUSSION: Tamoxifen use may improve long-term survival and quality-adjusted survival among women who are at increased risk of breast cancer, but this benefit diminishes with age. Tamoxifen is cost-effective in comparison with other cancer treatment strategies for younger women only.

Adult↗

PubMedDate not supplied

Time until first significant difference in in vivo tumor growth experiments.

In in vivo tumor growth experiments it is common to report the tumor measurement time at which the volume distributions of the treatment groups become significantly different. This method of analysis, as commonly practiced, is deficient in that its type I error rate exceeds the usual nominal rate of 5%, unless one specifically corrects for multiple comparisons. A second problem is that many investigators evidently interpret the time of first significance as a statistical parameter--i.e., a fixed but unknown property of the model that one can estimate by experimentation. In fact the time until first significance, like the power of the test, depends both on true model parameters (such as mean growth curves and experimental variability) and on features of the experimental design, such as the sample size and the spacing of the measurement times. We argue that investigators would do better to compare treatment groups by modeling tumor growth curves or estimating volume doubling times.

Animals↗

PubMedDate not supplied

Treatment of human glioblastoma cells with the staurosporine derivative CGP 41251 inhibits CDC2 and CDK2 kinase activity and increases radiation sensitivity.

CGP, 41251, a staurosporine derivative, is a potent inhibitor of protein kinase C (PKC). In recent studies we found that this compound causes growth inhibition and induces apoptosis in human glioblastoma cell lines and also inhibits the growth of xenografts of a human astrocytoma. In this study we investigate its effects on cell cycle control. Treatment of glioblastoma or gliosarcoma cells with CGP 41251 lead to a time and dose dependent increase of the percentage of cells in the G2-M phase of the cell cycle. This correlated with a decrease of CDC2- and CDK2-associated histone H1 kinase activities as well as a decrease in the cellular level of the CDC2 protein. The decrease of CDC2- associated histone H1 kinase activity was detected within 5 hours, and there was complete inhibition after 24 hours. Assays of mixtures of cell extracts obtained from cultures treated with CGP 41251, the inactive analog CGP 42700, or untreated cultures indicated that this decrease was due to a decrease in the CDC2 kinase itself rather than the accumulation of an inhibitor of this kinase. In vitro assays in which CGP 41251 was added directly to the in vitro assay system revealed marked inhibition of both CDC2- and CDK2-associated kinase activity at about 1 microM. Thus CGP 41251 inhibits CDC2- and CDK2-associated kinase activities both in vivo and in vitro. Its biologic effects may, therefore, not be due simply to inhibition of PKC. Since cells in the G2-M phase of the cell cycle are relatively more sensitive to killing by gamma- radiation than cells in other phases of the cell cycle, we carried out radiosensitization studies. We found that CGP 41251 was a radiation sensitizer in two glioblastoma cell lines. Therefore, this compound may be useful in the treatment of glioblastomas, possibly in combination with radiation therapy.

Antineoplastic Agents↗

PubMedDate not supplied

Growth inhibition induced by Ro 31-8220 and calphostin C in human glioblastoma cell lines is associated with apoptosis and inhibition of CDC2 kinase.

Protein kinase C (PKC) is a central component in signal transduction and growth control and might be an appropriate target for the chemotherapy of human brain tumors. This study demonstrates that the staurosporine derivative Ro 31-8220, a potent PKC inhibitor, inhibited the growth of 7 human brain tumor cell lines with an IC50 of about 2 microM. Calphostin C, a structurally unrelated PKC inhibitor, inhibited the growth of two of these cell lines with an IC50 of about 100 to 300 nM. Drug withdrawal and clonogenicity assays indicated that the growth inhibition by both of these compounds was irreversible. Morphologic studies, DNA fragmentation studies and flow cytometric assays showed that the treated glioblastoma cells underwent apoptosis. Treatment of glioblastoma cells with Ro 31-8220 lead to a rapid decline in the level of the anti-apoptosis protein bcl-2. At least three of the glioblastoma cell lines carried mutant p53 alleles with missense mutations in the DNA binding domain of p53. Therefore, the induction of apoptosis in these cell lines occurred through a p53-independent mechanism. Furthermore treatment of these glioblastoma cell lines with Ro 31-8220 or calphostin C led to an increase of cells in the G2-M phase of the cell cycle. This correlated with a decrease in CDC2-associated histone H1 kinase activity, as well as a decrease in the level of the CDC2 protein as shown by immunoblotting. When added to subcellular assays Ro 31-8220 markedly inhibited CDC2 histone H1 kinase activity with an IC50 of 100 nM, but calphostin C directly inhibited this kinase activity only at very high concentrations (above 100 microM). Thus these compounds inhibit the growth of glioblastoma cells through novel mechanisms. Ro 31-8220, in particular, might be a useful agent for the treatment of human brain tumors.

Anticarcinogenic Agents↗