Navegando por Assunto "Tumores cerebrais"

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Acesso aberto (Open Access)
Análise de alterações no número de cópias envolvendo os cromossomos 1p e 22 em meningiomas de baixo grau
(Universidade Federal do Pará, 2013-12-13) SILVA, Geanny Pereira da; OLIVEIRA, Edivaldo Herculano Correa de; http://lattes.cnpq.br/0094007714707651
Meningiomas are the second most common type of primary brain tumor, originating in the meninges covering the brain and spinal cord. They show slow growth, and are found more often in the CNS, being benign in most case, although there are also cases of meningiomas classified as malignant. At the cytogenetic level, meningiomas are the most well studied tumors in humans: studies in CNS tumors have shown that most cases had chromosomal abnormalities, and the most common alterations in theis type of tumor are the loss of one copy of chromosome 22 and deletion of the short arm of chromosome 1. These alterations have been associated with the tumorigenesis process, because they are found mostly in low-grade tumors, particularly deletions involving chromosome 22. Thus, the aim of this study was to analyze the occurrence of copy number alterations (CNAs) involving chromosomes 1p and 22 meningiomas grade I and II, and in addition to verifying the existence of other recurrent rearrangements through the application of high resolution comparative genomic hybridization (array - CGH ). Tumor samples were collected from eight patients. All samples showed gains and losses of various chromosomal segments. Except for one case, all others showed, in different degrees though, more deletions than amplifications. Loss of 1p segments was observed in all samples. Some CNAs were recurrent, being found up to six out of the eight cases. Pair 22 showed CNV in all samples, but the total monosomy was observed in only two of the eight samples. The global analysis of CNAs in all samples showed that, although changes 1p and 22 were the most frequent observed alterations, as expected, other genomic regions had also alterations in various samples, indicating a possible involvement of these modifications in the process of tumorigenesis and tumor progression. For instance, alterations in pairs 9, 12 and 17, have been observed in other studies and were correlated with atypical and anaplastic meningiomas. Our data indicate the existence of a larger number of genomic alterations in low-grade meningiomas, disagreeing partly with the assumption that these tumors are characterized by a small number of changes, usually involving pair 22 and, less frquently, loss of 1p. However, the fact that these tumors present alterations that are classically found in meningiomas, even benign, such as deletions in 1p and 22q, may be an indication that these changes must be linked with the early events of origin in meningiomas, as already suggested several times by other authors . In conclusion, these alterations remain important markers in meningiomas, and the relationships of these and other CNAs with the response to different treatments and recurrences should be the next step after cytogenomic characterization based on array-CGH has been completed.
Acesso aberto (Open Access)
Classificação de tumores cerebrais: um estudo comparativo entre rede neural convolucional e rede neural convolucional com mecanismo de atenção
(Universidade Federal do Pará, 2024-09-30) SILVA, Ulrich Kauê Mendes Alencar da; CASTRO, Adriana Rosa Garcez; http://lattes.cnpq.br/5273686389382860
Brain tumors are neurological diseases with a high potential impact on the lives of affected individuals, requiring a rapid and accurate diagnosis through complementary imaging tests, such as magnetic resonance imaging, which is considered the gold standard in this process. Considering the need for faster diagnosis, classification systems based on Machine Learning have been developed and within this context, this dissertation aims to present a comparative study between a Convolutional Neural Network (CNN) and a CNN with an attention mechanism, developed for the classification of brain tumors from magnetic resonance images. The comparative study aims to identify the impact of the attention mechanism on the performance of the CNN for tumor classification. For the development and evaluation of the proposed models, a public database was used, collected from the Kaggle website and made available by Masoud Nickparvar, which is composed of 7023 brain magnetic resonance images, segmented into four classes: glioma, meningioma, no tumor and pituitary. As a result, from the performance metrics obtained, considering the image base used for testing in both CNNs, an improvement in the CNN performance was observed after the introduction of the attention mechanism, where the network with this mechanism presented an increase of 1.98% in the accuracy metric, 2.07% in the precision metric, 2.18% in the sensitivity metric and 1.72% in the F1-score metric in relation to the CNN without the attention mechanism. It is also possible to highlight the results obtained in particular for the meningioma tumor class, since the CNN without the attention mechanism presented difficulties in classifying this class and, after the integration of the attention mechanism, the model obtained an accuracy increase of 6.54% for this class.
Acesso aberto (Open Access)
Epigenetic alterations in human brain tumors in a Brazilian population
(2006) ANSELMO, Nilson Praia; BELLO, Maria Josefa; GONZALEZ-GOMEZ, Pilar; DIAS, Luis Antonio Araújo; ALMEIDA, José Reinaldo Walter de; SANTOS, Marcelo José dos; HERRANZ, Juan Antonio Rey; CASARTELLI, Cacilda
Aberrant methylation of CpG islands located in promoter regions represents one of the major mechanisms for silencing cancer-related genes in tumor cells. We determined the frequency of aberrant CpG island methylation for several tumor-associated genes: DAPK, MGMT, p14ARF, p16INK4a, TP73, RB1 and TIMP-3 in 55 brain tumors, consisting of 26 neuroepithelial tumors, 6 peripheral nerve tumors, 13 meningeal tumors and 10 metastatic brain tumors. Aberrant methylation of at least one of the seven genes studied was detected in 83.6% of the cases. The frequencies of aberrant methylation were: 40% for p14ARF, 38.2% for MGMT, 30.9% for, p16INK4a, 14.6% for TP73 and for TIMP-3, 12.7% for DAPK and 1.8% for RB1. These data suggest that the hypermethylation observed in the genes p14ARF, MGMT and p16INK4a is a very important event in the formation or progression of brain tumors, since the inactivation of these genes directly interferes with the cell cycle or DNA repair. The altered methylation rate of the other genes has already been reported to be related to tumorigenesis, but the low methylation rate of RB1 found in tumors in our sample is different from that so far reported in the literature, suggesting that perhaps hypermethylation of the promoter is not the main event in the inactivation of this gene. Our results suggest that hypermethylation of the promoter region is a very common event in nervous system tumors.