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 drug-resistant 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.

To correlate Helicobacter pylori (H. pylori), Epstein-Barr virus (EBV) and human papillomavirus (HPV) with gastric cancer (GC) cases in Pará State, Brazil. Tissue 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. The 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. HPV 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.