Browsing by Autor "Hsieh, Ricardo"

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MAP Kinase Pathways: Molecular Roads to Primary Acral Lentiginous Melanoma.
(2015) Fernandes, Juliana D; Hsieh, Ricardo; de Freitas, Luiz A R; Brandao, Miguel A R; Lourenço, Silvia V; Sangueza, Martin; Nico, Marcello M S
The etiology and pathogenesis of lentiginous acral melanomas are poorly understood. Recent studies have postulated that DNA repair mechanisms and cell growth pathways are involved in the development of melanoma, particularly changes in the MAPK pathways (RAS, BRAF, MEK 1/2, and ERK 1/2). The aim of this study is to assess the status of the MAP kinase pathways in the pathogenesis of acral melanomas. The authors examined the components of the RAS-RAF-MEK-ERK cascades by immunohistochemistry in a series of 16 primary acral melanomas by tissue microarray. The expression of MAP kinase cascade proteins changed in most cases. The authors observed that 57.14% of cases were BRAF positive and that 61.53%, 71.42%, and 71.42% of cases were positive for MEK2, ERK1, and ERK2, respectively; RAS was not expressed in 92.31%, and all cases were negative for MEK1. The absence of RAS and positivity for MEK2, ERK1, and ERK2 were most seen in invasive cases with high thickness. These aspects of the MAPK pathway require further examination in acral melanomas between different populations. Nevertheless, the results highlight significant alterations in the MAP kinase cascades that are related to histological indicators of prognosis in primary acral melanomas.
Mutational Status of NRAS and BRAF Genes and Protein Expression Analysis in a Series of Primary Oral Mucosal Melanoma.
(2017) Hsieh, Ricardo; Nico, Marcello M S; Camillo, Cláudia M C; Oliveira, Kátia K; Sangueza, Martin; Lourenço, Silvia V
Primary oral mucosal melanoma is an extremely rare and aggressive tumor arising from melanocytes located in the mucosal epithelium of the oral cavity. Although malignant melanoma of oral mucosa shares some clinical features with its cutaneous counterpart, it has been associated with a worst prognosis; its etiopathogenesis are still only partially unraveled as there is no influence of UV radiation. It is known that the mitogen-activated protein kinase pathway mediates cellular responses to growth signals and its activation is an important phenomenon in melanoma. The aim of this study was to evaluate NRAS and BRAF genes, both components of mitogen-activated protein kinase molecular pathway, and compare with their protein expression. Point mutations of NRAS (codons 12, 13, and 61) and BRAF (codon 600) were screened by pyrosequencing method, and its results were associated to the protein expression of RAS and BRAF performed by immunohistochemistry. The authors observed mutation in BRAF 600 (3/14), NRAS codons 12 and 13 (2/14), and NRAS codon 61 (2/8). One case showed positive RAS protein expression, but no mutation was observed. Twelve in 14 cases showed positive BRAF protein expression: 3 cases showed BRAF mutation; 2 cases showed NRAS codon 61 mutation; 2 cases showed NRAS codons 12 and 13 mutation but not simultaneously. Although NRAS and BRAF mutation frequency and RAS protein expression are low, BRAF protein expression was intense; probably, NRAS and BRAF mutations are independent events and alternative molecular mechanisms in the primary oral mucosal melanoma tumorigenesis.