AIMTo correlate Helicobacter pylori (H. pylori), Epstein-Barr virus (EBV) and human papillomavirus (HPV) with gastric cancer (GC) cases in Pará State, Brazil.METHODSTissue samples were obtained from 302 gastric adenocarcinomas. A rapid urease test was used to detect the presence of H. pylori, and the presence of the cagA gene in the HP-positive samples was confirmed by PCR. An RNA in situ hybridization test designed to complement Eber1 RNA was used to detect the presence of EBV in the samples, and the L1 region of HPV was detected using nested PCR. Positive HPV samples were genotyped and analyzed for E6 and E7 viral gene expression. Infections were also correlated with the clinical and pathological characteristics of the patients.RESULTSThe majority of the 302 samples analyzed were obtained from men (65%) aged 55 years or older (67%) and were classified as the intestinal subtype (55%). All three pathogens were found in the samples analyzed in the present study (H. pylori: 87%, EBV: 20%, HPV: 3%). Overall, 78% of the H. pylori-positive (H. pylori+) samples were cagA+ (H. pylori-cagA+), and there was an association between the cytotoxic product of this gene and EBV. Coinfections of H. pylori-cagA+ and EBV were correlated with the most advanced tumor stages. Although only 20% of the tumors were positive for EBV, infection with this virus was associated with distant metastasis. Only the HPV 16 and 18 strains were found in the samples, although no expression of the E6 and E7 oncoproteins was detected. The fundus of the stomach was the region least affected by the pathogens.CONCLUSIONHPV was not involved in gastric tumorigenesis. Prophylactic and therapeutic measures against H. pylori and EBV may prevent the development of GC, especially the more aggressive forms.

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Many types of cancer are initially susceptible to chemotherapy, but during treatment, patients may develop resistance to therapy. Knowing that acquisition of drug resistance is a major clinical problem in antineoplastic treatment, the present work aimed to present, through a literature review, the development of chemoresistant cells lines as a model in experimental oncology. A total of 110 drugresistant cell lines, mainly from lung tumors and leukemias, have been developed. In addition, it has been observed that the drugs used for induction of resistance represented the drugs used for first-line treatment of each neoplasia, since the ideal chemotherapeutic treatment to induce resistance in vitro aims at a better modulation of the therapeutic response in order to better study the mechanisms of resistance. Normal tissue controls the production and release of growth promoting signals that regulate the initiation and progression of the cell cycle, ensuring cellular homeostasis and maintainance of healthy tissue architecture and function. Cancer cells exhibit deregulation of these signals and may acquire the ability to maintain continuous and abnormal proliferative signaling, inhibition of growth suppressors, resistance to cell death, replicative immortality, angiogenesis and metastasis that leads to an inadequate and pathogenic functioning of the tissue in which they occur (1-4). The literature shows that, in the tumor model, cancer cells originate from a single cell that has important stem cell characteristics, including the unlimited potential for replication and mechanisms of protection from xenobiotic agents. These findings have a significant effect on cancer treatment, since traditional antineoplastic treatment was based on the assumption that all somatic cells have a similar malignant potential, and the lack of specificity in combating these characteristics has rendered the therapies ineffective in providing a lasting response to cancer (5, 6). Chemotherapy is one of the pillars of clinical cancer treatment, but its outcome usually culminates in multidrug resistance (MDR), a phenomenon that can be found in several cells present in the tumor microenvironment, drastically restricting and the curative effect of drugs for a variety of tumors (7-9). Although many types of cancer are initially susceptible to chemotherapy, over the course of the therapeutic regimen, some patients may develop therapeutic resistance, due to several intracellular mechanisms including genetic and epigenetic changes in signaling pathways of survival, drug metabolizing enzymes and drug efflux pump mechanisms. Epigenetic modifications also act as an important set of mechanisms that lead to resistance in cancer treatment, and the main ones include DNA methylation and histone acetylation that can influence carcinogenesis because they deregulate normal expression of genes (Figure 1) (10, 11). The most studied mechanism of resistance to drugs against cancer involves the reduction of the intracellular concentration of the drug by increasing drug ...

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