Biomedical subjects

M Partridge

Publications and source records attributed to M Partridge.

At least 37 records · Page 2Linked to original sources

PubMed2001

Profiling clonality and progression in multiple premalignant and malignant oral lesions identifies a subgroup of cases with a distinct presentation of squamous cell carcinoma.

A cohort of head and neck cancer patients, without exposure to tobacco and alcohol, presented with multiple preneoplastic and neoplastic lesions, the natural history of which may span several decades. Examination of these cases provides an opportunity to study the relationship between genetic, morphological, and clonal progression in these fields and establish whether they represent a unique presentation of squamous cell carcinoma. The presence of a common novel microsatellite allele, a common breakpoint or concordant allelic imbalance at multiple loci, reveals that a high proportion of these serial lesions arise due to spread of a precursor. The tumors arising in these patients were typically nonaggressive, although metastases developed at a late stage, supporting the notion that the genotype results in a phenotype with a propensity for lateral spread, rather than invasion. Different genetic aberrations were detected in morphologically similar phenotypes such that no consistent early or late events were associated with development of premalignant lesions. Combining information about the clinicopathological features and histological examination of the margins with that derived from clonality analysis reveals that a subgroup of patients, without exposure to the traditional risk factors associated with this disease, developed multiple clonally related oral lesions and represents a unique presentation of head and neck squamous cell carcinoma. We suggest the term clonal cancerization to describe multiple premalignant and malignant lesions when there is conclusive evidence that they arise due to lateral spread from a common precursor.

Adult↗

PubMed2000

A case-control study confirms that microsatellite assay can identify patients at risk of developing oral squamous cell carcinoma within a field of cancerization.

Distinguishing true precursor lesions on the basis of clinical or histological features alone is unreliable but is important so that appropriate intervention can be instigated. Preliminary studies have shown that a microsatellite assay may provide important new prognostic information. To build on these observations, we have performed a case-control study to establish whether we can be confident about incorporating this new information into clinical practice. We have determined the frequency of allelic imbalance (AI) within key chromosomal regions, by matching 39 cases with dysplastic oral lesions that developed a tumor on the same side of the mouth, for as many variables as possible, with controls presenting with similar lesions that did not progress to malignancy when followed for the same period. Our findings confirm that the group that developed tumor had precursor lesions that harbor AI at more loci (P = 0.002). However, no consistent patterns of AI were associated with the three grades of dysplasia: mild, moderate, and severe. One-third of the tumors developed at the same site as the dysplastic lesion and two-thirds at a different site, which revealed that the presence of these aberrations in a dysplastic lesion provided information about the risk of malignant change within a larger field. This suggests that the process of field cancerization is more widespread than previously recognized. On the basis of these findings, we advocate complete excision of all suspicious areas that show AI at two or more key loci, regardless of the degree of dysplasia. However, because the remaining mucosa is also "at risk," these cases should also be targeted to receive dietary advice and chemoprevention, to minimize their risk of tumor formation at a distant site.

Adult↗

PubMed2000

The delivery of intensity modulated radiotherapy to the breast using multiple static fields.

BACKGROUND AND PURPOSE: To develop a method of using a multileaf collimator (MLC) to deliver intensity modulated radiotherapy (IMRT) for tangential breast fields, using an MLC to deliver a set of multiple static fields (MSFs). MATERIALS AND METHODS: An electronic portal imaging device (EPID) is used to obtain thickness maps of medial and lateral tangential breast fields. From these IMRT deliveries are designed to minimize the volume of breast above 105% of prescribed dose. The deliveries are universally-wedged beams augmented with a set of low dose shaped irradiations. Dosimetric and planning QA of this method has been compared with the standard, wedged treatment and the corresponding treatment using physical compensators. Several options for delivering the MSF treatment are presented. RESULTS: The MSF technique was found to be superior to the standard technique (P value=0.002) and comparable with the compensated technique. Both IMRT methods reduced the volume of breast above 105% dose from a mean value of 12.0% of the total breast volume to approximately 2.8% of the total breast volume. CONCLUSIONS: This MSF method may be used to reduce the high dose volume in tangential breast irradiation significantly. This may have consequences for long-term side effects, particularly cosmesis.

Breast Neoplasms↗

PubMed2000

The FHIT gene in oral squamous cell carcinoma: allelic imbalance is frequent but cDNA aberrations are uncommon.

The FHIT (fragile histidine triad) gene at chromosome 3p14.2 spans the FRA3B fragile site and encodes for a diadenosine triphosphate hydrolase-type protein. FHIT is frequently abnormal in solid tumours including those of the upper aerodigestive tract (UAT) and has therefore been proposed as a tumour-suppressor gene. This proposition was evaluated here for oral squamous cell carcinoma (SCC) using microsatellite analysis, reverse transcription-polymerase chain reaction (RT-PCR), FHIT exon 5 PCR and direct sequencing. Fifty-eight primary oral SCCs were examined with two FHIT gene microsatellite markers (D3S4103 and D3S1300) and two markers flanking FHIT. Allelic imbalance (AI) occurred in 28 of 52 informative cases (54%) at one or both FHIT markers (D3S4103: 53%; D3S1300: 42%). A significant association was noted between frequency of AI and advanced stage tumours for D3S4103 but not between AI frequency and smoking. AI frequency at D3S1300 and at a flanking marker correlated with low survival. Of eight oral/UAT SCC cell lines examined, six produced abundant wild-type transcript and one yielded mostly truncated transcripts, the most abundant of which lacked exons 5-7. A double deletion was also detected in one of 11 primary oral SCCs. Our microsatellite assay results show that the FHIT gene is frequently disrupted in oral SCC. However, as FHIT was shown to be expressed normally in the great majority of oral/UAT SCCs studied, its likely involvement in the molecular pathogenesis of the disease as a tumour suppressor remains doubtful.

Acid Anhydride Hydrolases↗

PubMed2000

Reconstruction of megavoltage photon spectra from electronic portal imager derived transmission measurements.

Three variants of the Schiff equation are investigated to model the spectra produced by megavoltage linear accelerators. These models are tested against well-validated Monte Carlo (MC) generated spectra on the central axis of large-area fields, and show excellent agreement. Numerical reconstructions of 6 and 10 MV spectra using the same models are then presented, using experimental attenuation data derived from an electronic portal imager. The process of deriving spectra from experimental attenuation data is shown to be inherently badly constrained mathematically, with the derived spectrum being highly sensitive to noise in the source data, and non-unique. By placing a priori constraints on the Schiff model from both physical knowledge of the construction of the accelerator and MC data, physically useful results are gained and presented for both the energy dependence and off-axis behaviour of photon spectra.

Calibration↗

PubMed2000

IMRT verification with a camera-based electronic portal imaging system.

An evaluation of the capabilities of a commercially available camera-based electronic portal imaging system for intensity-modulated radiotherapy verification is presented. Two modifications to the system are demonstrated which use a novel method to tag each image acquired with the delivered dose measured by the linac monitor chamber and reduce optical cross-talk in the imager. A detailed performance assessment is presented, including measurements of the optical decay characteristics of the system. The overall geometric accuracy of the system is determined to be +/-2.0 mm, with a dosimetric accuracy of +/-1.25 MU. Finally a clinical breast IMRT treatment, delivered by dynamic multileaf collimation, is successfully verified both by tracking the position of each leaf during beam delivery and recording the integrated intensity observed over the entire beam.

Breast Neoplasms↗

PubMed2000

A method of improving the spatial resolution of treatments that involve a multileaf collimator.

In this paper we present a novel method of reducing the dosimetric effects of the finite leaf width of a multileaf collimator (MLC) in conformal and intensity modulated radiotherapy (IMRT). This is achieved by decomposing the required high-resolution fluence distribution into two orthogonal components, which are delivered with two leaf sweeps with head-twists differing by 90 degrees. Before the decomposition stage, a filter is applied to the required beam to force it to have a constant gradient in the two delivery directions. The component deliveries were found to be very spiky in nature, resulting in very inefficient delivery with the scanning leaves of our MLC. This method was evaluated using film dosimetry of four idealized beams: a 45 degree edge, a circle, a hemispherical intensity modulated beam (IMB) and a sine-like IMB. The measurements showed that this method had significantly reduced the effects of the 1 cm leaf width of our MLC at the 50% isodose level, but there was significant overdosage at the edge of the field and immediately inside the held edge. This method shows promise but further work is required before it may find clinical utility.

Algorithms↗

PubMed2000

Direct measurement and analytical modeling of scatter in portal imaging.

In this study a direct measurement of scatter in portal imaging for various air gaps and scatterer thicknesses at a beam energy of 6 MV is presented. The experimental data are compared with results from a Monte Carlo (MC) scatter model. In the regime where the air gap is larger than 9.3 cm the MC and the experiment agree. Based on this MC model an analytical model is developed, which takes all important interaction processes into account. It comprises a rigorous treatment of first order scattering and an estimation of photons scattered more than once within the phantom. This estimation is based on the assumption that higher order scattering can be considered as isotropically distributed around a certain scatter origin located in the midplane of the phantom. It is found that relative deviations between the MC model and the analytical model are of 2% to 3% in regions where scattering is very large.

Biophysical Phenomena↗

PubMed2000

Leaf position verification during dynamic beam delivery: a comparison of three applications using electronic portal imaging.

The use of a dynamic multileaf collimator (MLC) to deliver intensity-modulated beams presents a problem for conventional verification techniques. The use of electronic portal imaging to track MLC leaves during beam delivery has been shown to provide a solution to this problem. An experimental comparison of three different verification systems, each using a different electronic portal imaging technology, is presented. Two of the systems presented are commercially available imagers with in-house modifications, with the third system being an in-house built experimental system. The random and systematic errors present in each of the verifications systems are measured and presented, together with the study of the effects of varying dose rate and leaf speed on verification system performance. The performance of the three systems is demonstrated to be very similar, with an overall accuracy in comparing measured and prescribed collimator trajectories of approximately +/-1.0 mm. Systematic errors in the percentage delivered dose signal provided by the accelerator are significant and must be corrected for good performance of the current systems. It is demonstrated that, with suitable modifications, commercially available portal imaging systems can be used to verify dynamic MLC beam delivery.

Algorithms↗

PubMed2000

Oral cancer: 1. The genetic basis of the disease.

This article is in two parts. The first describes recent advances in our understanding of the biology of oral cancer and the potential to utilize this new information to make better predictions about outcome and devise new treatments. The second part describes the clinical presentation and the development of a new generation of ultra-sensitive diagnostics to identify occult tumour and precancer, to investigate why cancer may recur.

Apoptosis↗

PubMed2000

Detection of minimal residual cancer to investigate why oral tumors recur despite seemingly adequate treatment.

Improvements in surgery and radiotherapy techniques have led to only a modest increase in the 5-year survival rate for patients with head and neck cancer. This is because the pattern of clinical disease is changing, such that locoregional recurrence now accounts for fewer treatment failures, but more patients develop a second primary cancer or distant metastatic disease. In this study, we have used the p53 phage plaque assay, immunocytochemistry, and mutational analysis to assess the contribution of minimal residual cancer and genetic aberrations in clinically normal upper aerodigestive tract mucosa to treatment failure. Eighteen consecutive patients with oral tumors, with conventional clear margins, have been followed for a minimum of 36 months. Molecular assessment identified tumor-positive surgical margins for 6 of 11 assessable patients and additional tumor-positive lymph nodes for three cases. Disseminated malignant cells were detected in the hematopoietic cell compartment for six cases, and one patient had molecular evidence of field cancerization. Locoregional recurrence developed in five patients with tumors harboring a p53 gene mutation; four of these were associated with tumor-positive surgical margins, and one was associated with molecular evidence of field cancerization. Radiotherapy to the primary site did not prevent development of local recurrence when the residual tumor harbored a p53 gene mutation. Three of six cases with a tumor-positive bone marrow aspirate developed distant metastases. These findings reveal that molecular and immunocytochemical detection of minimal residual cancer and field cancerization can help identify patients who may develop locoregional or distant recurrence and justify further studies to evaluate the contribution of these remaining malignant cells to treatment failure.

Adult↗

PubMed1999

Location of candidate tumour suppressor gene loci at chromosomes 3p, 8p and 9p for oral squamous cell carcinomas.

To help define the location of tumour suppressor genes implicated in the pathogenesis of oral squamous cell carcinoma (SCC), we have used microsatellite assay and restriction fragment length polymorphism (RFLP) analysis to screen 48 primary SCC for allelic imbalance (AI) with 32 polymorphic markers at chromosome 3p, and prepared a detailed deletion map. The finding of a high frequency of AI at specific regions, together with the presence of multiple small interstitial deletions involving these loci, identifies 5 areas at this chromosome arm that may harbour tumour suppressor genes. No sequence aberrations affecting the von Hippel Lindau (VHL) and fragile histidine triad (FHIT) genes, which reside within the candidate tumour suppressor gene areas at this chromosome arm, were identified. A more limited analysis of polymorphic sequences at 8p and 9p supports the existence of at least 2 areas that harbour tumour suppressor genes at 8p and evidence that additional targets for deletion reside centromeric and telomeric to the p16 gene at 9p21.

Acid Anhydride Hydrolases↗

PubMed1999

Patient-specific mutation databases for oral cancer.

Development of databases, summarising the genetic events associated with oral squamous cell carcinoma (SCC), should increase our understanding of the molecular basis of these lesions. Additionally, databases will help establish whether different cancer subtypes show different growth characteristics, because the multistage carcinogenic process is different in the various tumour subtypes. This new knowledge may also provide new prognostic information, as these aberrations represent fundamental biological characteristics of each tumour. To assess the value of incorporating the results from loss of heterozygosity (LOH) analysis into patient-specific mutation databases, we have carried out microsatellite analysis with 52 polymorphic markers at 13 key chromosomal regions implicated in the pathogenesis of head and neck cancers. Altered expression of the Rb, p53 and DCC tumour suppressor genes has also been studied by immunohistology. Our results shed light on the different pathways that lead to cancer and reveal that a variety of different patterns of allelic imbalance (AI) were detected at all TNM stages, reflecting the different clinical behaviour that tumours classified as being of the same TNM stage may exhibit. Summarising the level of genetic damage as a fractional allelic loss (FAL) score and the presence of AI at 3p22-26, 3p14.3-12.1 and 9p21 was found to be a better predictor of outcome than the TNM system. This finding suggests that molecular data can be incorporated into conventional staging systems to provide more accurate prognostic information for this group of patients.

Adult↗

PubMed1999

Immunomagnetic separation for enrichment and sensitive detection of disseminated tumour cells in patients with head and neck SCC.

Screening for malignant cells in the blood and bone marrow was introduced as a strategy for the improved detection of tumour spread and may predict the development of distant metastases. The sensitivity of these approaches depends on several factors, including the choice of antibody for immunocytochemistry (ICC) and the number of cells examined. In this study criteria have been defined for scoring cells reactive with a pan-cytokeratin antibody as tumour, by comparing immunostained cells in clinical samples obtained from head and neck cancer patients and a control group without epithelial malignancy. When leucocyte subfractions are prepared by density gradient separation (DGS) from central venous blood obtained from patients with advanced head and neck squamous cell carcinoma (SCC) and screened by ICC, epithelial tumour cells sediment preferentially with the mononuclear cells but may also be detected in the granulocyte (GC) fraction. Some cases were found to have more tumour cells in the GC fraction. Similar results were seen in model experiments. To increase the sensitivity of the ICC approach, the efficiency of positive immunomagnetic selection (IMS) using Dynabeads coated with an antibody recognizing the Ber-EP4 epitope has been compared with negative IMS using anti-CD45 Dynabeads. Tumour cells were recovered from bone marrow aspirates for 2/17 cases using the positive enrichment technique and for 11/17 patients following negative IMS. These findings justify prospective studies incorporating negative IMS to establish the prognostic significance of these disseminated tumour cells for this group of patients.

Antigens, Neoplasm↗

PubMed1999

New insights into p53 protein stabilisation in oral squamous cell carcinoma.

p53 is a transcription factor which regulates cell proliferation and apoptosis to prevent division of potentially malignant cells. In many tumours mutation of the p53 gene leads to stabilisation of this protein which can be detected by immunohistochemistry (IHC). However, there are many reports describing detection of p53 by IHC in the absence of gene mutation, and in these cases other factors stabilise p53. To shed light on the mechanisms which permit detection of this protein in these mutation-negative cases we have examined 45 primary oral squamous cell carcinomas (SCCs) by IHC and gene sequencing for p53 (exons 4-8) and related the results to a FAL score (determined using microsatellite assay and expressing the number of loci showing allelic imbalance as a fraction of the total number of informative markers for each case). We also investigated the pattern of MDM2 expression in these tumours. High levels of p53 protein were detected in 24/45 cases and point mutations involving exons 4-9 were seen in 11 cases. A further four cases harboured deletions or a stop codon. For 6/48 cases there was concordance of AI within the p53 gene and mutation. However nine cases showed p53 mutation only and 5 AI without mutation, suggesting that oral tumours frequently retain one normal p53 allele. Detection of p53 by IHC correlated strongly with the FAL score. Thus whilst it is possible that some tumours harbour p53 mutations outside the open reading frames examined, or are missed due to sequencing a mixture of normal and tumour tissue, a subgroup of tumours may express high levels of wild-type p53 as a reflection of the high FAL score and ongoing genomic stress. Levels of MDM2 transcripts and protein were similar in all SCCs examined. However, MDM2 may be non-functional, or there may be defects affecting other important regulatory proteins in tumours which which express wild type p53 protein.

Adult↗

PubMed1999

The prognostic significance of allelic imbalance at key chromosomal loci in oral cancer.

Forty-eight primary oral squamous cell carcinomas (SCC) were screened for allelic imbalance (AI) at 3p24-26, 3p21, 3p13, 8p21-23, 9p21, 9q22 and within the Rb, p53 and DCC tumour suppressor genes. AI was detected at all TNM stages with stage 4 tumours showing significantly more aberrations than stage 1-3. A factional allelic loss (FAL) score was calculated for all tumours and a high score was associated with development of local recurrence (P = 0.033) and reduced survival (P = 0.0006). AI at one or more loci within the 3p24-26, 3p21, 3p13 and 9p21 regions or within the THRB and DCC genes was associated with reduced survival. The hazard ratios for survival analysis revealed that patients with AI at 3p24-26, 3p13 and 9p21 have an approximately 25 times increase in their mortality rate relative to a patient retaining heterozygosity at these loci. AI at specific pairs of loci, D3S686 and D9S171 and involving at least two of D3S1296, DCC and D9S43, was a better predictor of prognosis than the FAL score or TNM stage. These data suggest that it will be possible to develop a molecular staging system which will be a better predict of outcome than conventional clinicopathological features as the molecular events represent fundamental biological characteristics of each tumour.

Adult↗

PubMed1999

Role of p16/MTS1, cyclin D1 and RB in primary oral cancer and oral cancer cell lines.

One of the most important components of G1 checkpoint is the retinoblastoma protein (pRB110). The activity of pRB is regulated by its phosphorylation, which is mediated by genes such as cyclin D1 and p16/MTS1. All three genes have been shown to be commonly altered in human malignancies. We have screened a panel of 26 oral squamous cell carcinomas (OSCC), nine premalignant and three normal oral tissue samples as well as eight established OSCC cell lines for mutations in the p16/MTS1 gene. The expression of p16/MTS1, cyclin D1 and pRB110 was also studied in the same panel. We have found p16/MTS1 gene alterations in 5/26 (19%) primary tumours and 6/8 (75%) cell lines. Two primary tumours and five OSCC cell lines had p16/MTS1 point mutations and another three primary and one OSCC cell line contained partial gene deletions. Six of seven p16/MTS1 point mutations resulted in termination codons and the remaining mutation caused a frameshift. Western blot analysis showed absence of p16/MTS1 expression in 18/26 (69%) OSCC, 7/9 (78%) premalignant lesions and 8/8 cell lines. One cell line, H314, contained a frameshift mutation possibly resulting in a truncated p16/MTS1 protein. pRB was detected in 14/25 (56%) of OSCC but only 11/14 (78%) of these contained all or some hypophosphorylated (active) pRB. In premalignant samples, 6/8 (75%) displayed pRB, and all three normal samples and eight cell lines analysed contained RB protein. p16/MTS1 protein was undetectable in 10/11 (91%) OSCCs with positive pRB. Overexpression of cyclin D1 was observed in 9/22 (41%) OSCC, 3/9 (33%) premalignant and 8/8 (100%) of OSCC cell lines. Our data suggest p16/MTS1 mutations and loss of expression to be very common in oral cancer cell lines and less frequent in primary OSCC tumours. A different pattern of p16/MTS1 mutations was observed in OSCC compared to other cancers with all the detected p16/MTS1 mutations resulting in premature termination codons or a frameshift. The RB protein was expressed in about half (44%) of OSCCs and its expression inversely correlated with p16/MTS1 expression. In conclusion, we show that abnormalities of the RB pathway are a common mechanism of oral carcinogenesis.

Carcinoma, Squamous Cell↗

PubMed1999

A large-area ionization chamber for portal image calibration.

Methods of removing the effects of linear accelerator (linac) output fluctuation from electronic portal images are described and compared. The output of the linac is measured using a specially constructed large-area ionization chamber during imaging and recorded with the image. The use of a dose-rate signal directly from the linac monitor chamber is discussed. Various versions of a quadratic thickness calibration scheme are tested, incorporating linac output data measured by the ionization chamber. Experimental results are presented showing that the incorporation of data from the ionization chamber gives improved absolute calibration accuracy and flatness. Immediately after calibration, the mean systematic thickness error in calibration of a uniform 136.8 mm water-equivalent slab was shown to be no more than 0.6 mm with a thickness variation within each image also of no more than +/-0.8 mm. This was true even when imaging with an unstable linac beam giving mean thickness errors between images of 8.8 mm and variations within each image of +/-4.9 mm without the ionization chamber correction. Up to one month after calibration, use of the ionization chamber to remove short-term linac fluctuations is shown to still keep mean thickness errors to less than 1.6 mm with variations within each image of no more than +/-1.4 mm.

Calibration↗