Biomedical subjects

Stephen A Roberts

Publications and source records attributed to Stephen A Roberts.

11 recordsLinked to original sources

PubMed2007

Models for assisted conception data with embryo-specific covariates.

Assisted conception routinely involves multiple embryo implantation within each recipient mother, with the outcome of interest being the number and multiplicity of live births. Here we consider the situation in which covariate information, potentially predictive of outcome, is available at the embryo level for each individual implanted embryo. This presents two challenges: firstly the outcome is measured at a higher, recipient, level than the covariates of interest; and secondly it is generally not known which of the implanted embryos developed to give a successful pregnancy. In practice such data have usually been analysed by aggregation of the embryo-level covariates to the recipient-level. Here we consider and compare two alternative approaches which respect the structure of the data alongside the aggregated approach. The first is a deterministic model with separate embryo and recipient success probabilities, each determined by a set of covariates, as first proposed by Spiers and extended by Zhou and Weinberg. The second is based on a multilevel model with the correlations between embryos in the same recipient modelled by a recipient level random effect. These models are compared using two real data sets, and the model properties further explored in a simulation study.

Analysis of Variance↗

PubMed2006

Why oral histopathology suffers inter-observer variability on grading oral epithelial dysplasia: an attempt to understand the sources of variation.

The present study attempted to assess the reasons behind the inter-observer variation in grading oral epithelial dysplasia (OED). Three oral pathologists and one general pathologist examined 68 histological slides of OED lesions of variable grade for scoring the presence of each individual characteristic of the architecture and cytology changes that were established by the 2005 WHO classification. The assigned features in each case were correlated with clinical outcomes to understand which features are more commonly associated with malignant transformation. Interestingly, for all individual characteristics, the pairwise inter-examiner and group kappa values ranged from poor to moderate. It appeared that for each characteristic separately there was much dissension. Despite these observations, comparing these data with that from our previous paper on the same slides showed that the inter-observer agreement on the degree of dysplasia either by using the new binary system of "low-risk" or "high-risk" or by using the 2005 WHO classification turned out to be better than the agreement on the individual characteristics of architecture and cytology changes. Certain features show significant association with the clinical outcomes. In the discussion, some explanations to help understanding the sources of variation in grading OED are put forward. In conclusion, grading dysplasia is not an exact science and pathologists are doing their best to reach optimal results. Improvement in the standard of the histopathology reporting of OED lesions could be achieved by consideration of several issues. Of these, there is need for a universal definition of the architectural and cytological features that are the basis of any OED grading process. A minimum dataset for reporting OED lesions should be set up. Also, the use of a consensus scoring process between two or more observers should be encouraged as this would improve inter-observer agreement.

Carcinoma in Situ↗

PubMed2006

Evaluation of a new binary system of grading oral epithelial dysplasia for prediction of malignant transformation.

The aim of this paper is to assess the reproducibility of a novel binary grading system (high/low risk) of oral epithelial dysplasia and to compare it with the WHO classification 2005. The accuracy of the new system for predicting malignant transformation was also assessed. Ninety-six consecutive oral epithelial dysplasia biopsies with known clinical outcomes were retrieved from the Oral Pathology archives. A pilot study was conducted on 28 cases to determine the process of classification. Four observers then reviewed the same set of H&E stained slides of 68 oral dysplastic lesions using the two grading systems blinded to the clinical outcomes. The overall inter-observer unweighted and weighted kappa agreements for the WHO grading system were Ks = 0.22 (95% CI: 0.11-0.35), Kw = 0.63 (95% CI: 0.42-0.78), respectively, versus K = 0.50 (95% CI: 0.35-0.67) for the new binary system. Interestingly, all pathologists showed satisfactory agreement on the distinction of mild dysplasia from severe dysplasia and from carcinoma in situ using the new WHO classification. However, assessment of moderate dysplasia remains problematic. The sensitivity and specificity of the new binary grading system for predicting malignant transformation in oral epithelial dysplasia were 85% and 80%, respectively and the accuracy was 82%. The new binary grading system complemented the WHO Classification 2005 and may have merit in helping clinicians to make critical clinical decisions particularly for the cases of moderate dysplasia. Histological grading of dysplasia using established criteria is a reproducible prognosticator in oral epithelial dysplasia. Furthermore, the present study showed that more consensus scoring on either the degree of dysplasia, assessment of risk or the presence of each morphological characteristic by a panel should be encouraged.

Biopsy↗

PubMed2006

Future acceptance of adolescent human papillomavirus vaccination: a survey of parental attitudes.

The main target group for vaccination against human papillomavirus (HPV), the sexually transmitted virus that causes cervical cancer, will be young adolescents. We undertook a population-based survey to assess parental consent and potential HPV vaccine uptake in eight secondary schools using stratified randomisation according to school type and ethnicity. Our results suggest that in socially and ethnically mixed populations such as Manchester, an HPV vaccine uptake rate of 80% may be achievable if the vaccine is perceived to be safe and effective. However, most parents lack knowledge about HPV and some are concerned about sexual health issues that would arise as part of a HPV vaccine programme. It will be important to raise general awareness of the role of HPV in cervical cancer without stigmatizing the vaccine.

Adolescent↗

PubMed2005

Ultrasound assessment of caudal catheter position in infants.

The positioning of caudally inserted epidural catheters is crucial to their effectiveness. However, level assessment can be difficult and time consuming. We report the use of ultrasound to assess the catheter position in three patients aged between 1 and 10 months. The advantages and disadvantages of this technique are discussed in relation to other methods of assessing caudal catheter placement.

Adenoma↗

PubMed2005

Design and analysis of clinical trials with clustering effects due to treatment.

Where patients receive therapy as a group, there are good theoretical reasons to believe that variation in the outcome will be smaller for patients treated in the same group than for patients treated in different groups. Similarly, where different therapists treat different groups of patients, outcome for patients treated by the same therapist may differ less than outcome for patients treated by different therapists. Clinical trials evaluating such therapies need to consider this potential lack of independence. As with cluster-randomized trials, this has implications for the precision of treatment effects estimates and statistical power. There are nevertheless differences between clustering due to the organization of treatment and that due to randomization. In cluster-randomized trials the distribution of cluster sizes in each treatment arm should be similar as a consequence of randomization unless there is differential loss to follow-up. With clustering due to therapy group or therapist, cluster size may differ systematically between treatment arms, due to size of therapy groups or differing health professional caseload. Intra-cluster correlation may also differ between treatment arms. The implications of differential cluster size and intracluster correlation for design and analysis will be illustrated by data from two trials, the first comparing nurse practitioner care with general practitioner care, and the second comparing a group therapy with individual treatment as usual. The special case where a group therapy or therapist is compared with an unclustered treatment is examined in detail using a simulation study. The implications of differential clustering effects for sample size and power are addressed. It is argued that the design and analysis of this type of trial should take account of possible heterogeneity in cluster size and intracluster correlation.

Cluster Analysis↗

PubMed2004

Hypoxia-inducible factor 1alpha expression as an intrinsic marker of hypoxia: correlation with tumor oxygen, pimonidazole measurements, and outcome in locally advanced carcinoma of the cervix.

PURPOSE: Hypoxia-inducible factor (HIF)-1alpha expression was studied retrospectively in locally advanced carcinoma of the cervix in relation to other methods for measuring/assessing tumor hypoxia and outcome after radiotherapy. EXPERIMENTAL DESIGN: HIF-1alpha expression was examined in formalin-fixed tumor biopsies using a semiquantitative scoring system and correlated with measurements of hypoxia obtained using oxygen electrodes, pimonidazole staining, and carbonic anhydrase 9. RESULTS: High HIF-1alpha expression showed a weak correlation with low pO2 (r = -0.26; P = 0.030; n = 72). Weak significant correlations were found between HIF-1alpha and pimonidazole staining (r = 0.34; P = 0.040; n = 36) and carbonic anhydrase IX (r = 0.27; P = 0.001; n = 160). There was no relationship with surviving fraction at 2 Gy. The relationship between HIF-1alpha expression and radiotherapy outcome was examined in 99 patients. HIF-1alpha expression did not correlate with disease stage, grade, tumor size, and patient age. HIF-1alpha alone was not a significant prognostic factor for disease-free survival, metastasis-free survival, or local recurrence-free survival. High HIF-1alpha expression tended to be associated with poor outcome in small tumors but good outcome in large tumors, with statistically significant interactions between HIF-1alpha and tumor size for survival (P = 0.046) and local control (P = 0.009). CONCLUSIONS: In this study, HIF-1alpha had no prognostic significance in locally advanced carcinoma of the cervix. The possible switch in large tumors for an association between high HIF-1alpha expression and good outcome might relate to tumor size-related changes in the balance of genes up-regulated by HIF-1alpha. Whereas angiogenesis-promoting genes might be preferentially up-regulated in small tumors, proapoptotic genes might be induced in large tumors. This hypothesis needs testing in future work.

Antigens, Neoplasm↗

PubMed2004

Bone mineral density in childhood survivors of acute lymphoblastic leukemia treated without cranial irradiation.

Adult survivors of childhood acute lymphoblastic leukemia (ALL) whose treatment included cranial irradiation (XRT) have reduced bone mineral density (BMD). Fifty-three survivors of ALL (aged 6-17 yr; 22 males and 31 females), who had completed their treatment without XRT, at least 1 yr previously, and 187 (5-19 yr; 86 males and 101 females) healthy controls were examined with dual energy x-ray absorptiometry of the total body and L1-L4 vertebrae and peripheral quantitative computer tomography at the distal and midradial sites. The total body and lumbar spine BMDs did not differ between the ALL survivors and controls. Distal radial trabecular BMD (difference, -0.080 mg/cm(3); 95% confidence interval, -0.139 to -0.020; P = 0.009), but not total BMD (difference, -0.006 mg/cm(3); confidence interval, -0.051 to 0.039; P = 0.80), was lower in ALL survivors compared with controls. At the midradial site, both endosteal (11% larger; P = 0.0001) and periosteal (4% larger; P = 0.001) circumferences were greater, and cortical thickness was thinner by 6% (P = 0.006) in the ALL subjects, leading to an increase in the axial moment of inertia in the ALL subjects (difference, 13%; P = 0.008). In conclusion, BMD, except at the radius, is normal in childhood survivors of ALL treated without XRT. At the midradial site, we speculate that ALL or its treatment resulted in endosteal bone loss and cortical bone thinning, but the axial moment of inertia and, hence, strength was maintained as a result of bone gain at the periosteal surface.

Adolescent↗

PubMed2004

Blood pressure and the cystic fibrosis gene: evidence for lower pressure rises with age in female carriers.

Individuals homozygous for the autosomal recessive disorder CF are known to have low blood pressure, thought to be caused by greatly increased sweat salt loss. We examined whether carriers of the CF gene also have low blood pressure. Our pilot studies had suggested an effect limited to females, leading to 2 further studies in white females. In the first, blood pressure was measured in 232 known CF mutation carriers and compared with 246 mutation-negative control subjects. The carriers showed a significantly lower rate of increase in systolic blood pressure with age than the controls, especially after age 50 (3.5% per decade compared with 5.4% per decade, P=0.010). In a small substudy, sweat sodium and chloride levels were highest in those CF carriers with the lowest blood pressures. In the second study, CF carrier status was investigated in 563 normotensive females and in 607 women with essential hypertension diagnosed to test whether a lower incidence of carriers in the hypertensives suggested a protective effect. Twenty-five of the normotensives (4.4%) were carriers compared with 21 (3.5%) of the hypertensive group (P=0.45). Older CF carrier females had lower systolic and diastolic pressures than matched control subjects, with a tendency for blood pressure to increase less with age. This could result in significant reduction in stroke and heart disease. The effect on blood pressure is insufficient to prevent hypertension, though it remains conceivable that the severity might be ameliorated in carriers.

Adult↗

PubMed2004

Compensation for changes in dose-rate in radical low-dose-rate brachytherapy: a radiobiological analysis of a randomised clinical trial.

BACKGROUND AND PURPOSE: This study reanalysed the results of the Cs-137 low-dose-rate brachytherapy trials for stage I and II cervix carcinoma at the Christie Hospital, Manchester, UK, in order to quantify the clinical outcome as a function of dose, and to extract radiobiological parameter values by modelling the data for local control and morbidity. PATIENTS AND METHODS: Kaplan-Meier survival curves and Cox regression analyses were used to analyse the time to event data. Linear-quadratic (LQ) analysis was also used in a mixture model, incorporating a half-time for repair, a time factor, and a heterogeneity function between patients. Full 5-year follow-up data were available for 339 patients receiving Cs-137 doses between 60 and 75 Gy delivered at 1.4-1.8 Gy/h, and 178 patients receiving a Ra-226 dose of 75 Gy at 0.5 Gy/h, using two insertions 7-10 days apart. RESULTS: With the increased dose-rate, a dose reduction between 20 and 25% was required to achieve a similar morbidity rate. This reduction had a detrimental effect on tumour control, by about 15% points. Unexpectedly, this loss in local control did not lead to a decrease in cancer-specific survival. For both tumour control and complications a high alpha/beta and short half-time for repair best fitted the data, suggesting that consequential late reactions may be responsible for much of the bowel and urinary morbidity after these short treatments. The variability in response between patients was greater (CV 40%) for morbidity than for tumour control (CV 17%), probably reflecting the greater variation in dose at the target tissue. There was no significant dependence on overall treatment time detected over the 7-10-day range of these treatments. CONCLUSIONS: The therapeutic ratio was somewhat less for the higher dose-rate, in agreement with radiobiological expectations, although cancer-specific survival was inexplicably unchanged. The LQ-parameter analysis suggests that high alpha/beta ratios and/or short repair half-times are applicable for both tumour and normal tissue responses in these treatments.

Brachytherapy↗

PubMed2003

Maternal serum activin, inhibin, human chorionic gonadotrophin and alpha-fetoprotein as second trimester predictors of pre-eclampsia.

OBJECTIVE: To compare the serum levels of human chorionic gonadotrophin (hCG), alpha-fetoprotein, activin A, inhibin A and inhibin isoforms containing pro and alphaC in the second trimester serum of women who subsequently developed hypertensive disorders of pregnancy with those who remained normotensive throughout pregnancy. DESIGN: Retrospective case-control study of 15-20 week serum samples matched for duration of storage at -20 degrees C. SETTING: Antenatal clinics at a teaching hospital in Scotland. SAMPLE: Second trimester serum samples of 39 women who subsequently developed pre-eclampsia, 31 who subsequently developed pregnancy-induced hypertension and 155 women who remained normotensive throughout pregnancy. MAIN OUTCOME MEASURES: hCG, alpha-fetoprotein, activin A, inhibin A and inhibin pro-alphaC serum levels. RESULTS: Activin A levels in serum were significantly elevated in women who later developed pregnancy-induced hypertension (26% increase compared with controls) and hCG levels were significantly elevated in women who later developed pre-eclampsia (24% increase compared with controls). alpha-Fetoprotein, inhibin A and inhibin pro-alphaC levels were not significantly elevated in the patient groups compared with their controls. CONCLUSIONS: A combination of analyses including second trimester serum activin A and hCG may yet prove to be helpful predictors of women at risk of hypertensive disorders of pregnancy. While the results proved significant, the effects reported in this study are too modest compared with natural variability to be useful as screening tools on their own.

Activins↗