Introducing infectious agents and cancer (original) (raw)
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Annals of Ibadan Postgraduate Medicine, 2007
The epidemiology of several types of cancers indicate the involvement of several transmissible agents in their development, and in most cases, these seem to be viruses. The classic examples are Burkitt's lymphoma, nasopharyngeal carcinoma (EBV), hepatocellular carcinoma (HBV), and cervical carcinoma (HPV). Most of these cancers show substantial variations in their incidence in different parts of the world and in particular countries, they present significant health problems. Worldwide, infections account for up to 20% of all cancers. Also, there is now ample evidence implicating infection with the Helicobacter pylori in the occurrence of gastric carcinoma and gastric lymphoma, and infection with Schistosoma haematobium in the occurrence of the squamous cell carcinoma of the urinary bladder.The impact of these infections on the burden of cancer worldwide is becoming increasingly evident because they are largely responsible for the cascade of opportunistic malignancies associated with AIDS. The burden is heaviest among populations in developing countries, reflecting the impact of very early infection with these agents on subsequent risk of cancer. There are currently no vaccines available to prevent these chronic infections, other than for HBV. As a result, changes in behaviour hold the most promise for prevention.
Causal role of infectious agents in cancer: An overview
Caspian Journal of Internal Medicine, 2017
Cancer is a complex group of diseases with multiple eventual causes. The underlying causes are not fully known. Thus, learning more about the known causes of cancer is an important issue. Moreover, among these factors, infection and its association to cancers is controversial. Although, it seems that the genome instability of the cells can initiate cancer development. The purpose of this review was to present the role of infection in the development of cancer. Infectious agents, such as hepatitis B (HBV) and C viruses (HCV), Epstein-Barr virus (EBV), human papillomavirus (HPV), human immunodeficiency virus type 1 (HIV-1), Helicobacter pylori (H. pylori) and Streptococcus bovis (S. bovis) contribute to the pathogenesis of different cancers. These cancers include hepatocellular carcinoma, Burkitt's lymphoma, nasopharyngeal carcinoma, cervical cancers, non-Hodgkin lymphoma, Kaposi sarcoma, adenocarcinoma and lymphoma. Screenings of infectious diseases in cancer patients may open up areas of research in the identification of optimizing cancer control strategies.
Springer eBooks, 2022
Infectious agents play an aetiologic role in approximately 20% of cancer cases worldwide. At least, more than ten pathogens, including viruses, parasites, and bacteria are known to contribute to oncogenesis either directly via the expression of their protein products or indirectly via chronic inflammation (Table 1). To date, there are seven oncogenic viruses [human papillomavirus (HPV), Epstein-Barr virus (EBV), hepatitis virus B and C (HBV and HCV), human T-cell lymphoma virus 1 (HTLV-1), Merkel cell polyomavirus (MCPyV), and Kaposi's sarcoma virus (KSVH or HHV8)], one oncogenic bacterium (Helicobacter pylori), and three oncogenic parasites (Schistosoma haematobium, Opithorchis viverrini, and Clonorchis sinensis), identified as cancer-related pathogens. HBV, HCV, HPV, and H. pylori account for approximately 5% of all cancer cases by leading to hepatocellular carcinoma, cervical cancer and stomach cancer, respectively (Vandeven and Nghiem 2014). Pathogens can generally be divided into direct and indirect carcinogens (Figure 1). The direct carcinogenic pathogens HPV, HTLV-1, EBV, MCPyV and KSVH share several similarities. At least a critical portion of the viral genome can generally be detected in each cancer cell resulting in the expression of viral oncogenes that disrupt cell-cycle checkpoints, inhibit apoptosis and contribute to cell immortalisation. In contrast, the indirect carcinogenic pathogens (HBV, HCV, H. pylori, S. haematobium, O. viverrini, and C. sinensis) do not induce expression of oncogenes, but instead their persistent infection leads to a chronic inflammatory state or immunosuppression that limits the antitumour immune surveillance mechanisms. Because persistent infection is a hallmark of oncogenic pathogens, there is a window of opportunity for cancer prevention by treating the pathogen before malignant progression. Viral oncogenic mechanisms generally include: genomic instability, high rates of cell proliferation, resistance to apoptosis, abnormal DNA repair mechanisms, cell polarity changes and interference with telomere shortening, which often coexist with evasion of the antiviral immune response (Morales-Sánchez and Fuentes-Pananá 2014). Viral persistence and/or latency, in which there is no or little production of viral particles are biologically compatible with the carcinogenic process, due to avoiding of cell death while maintaining the infectious agent hidden from the immune system. Viral persistence in the host is achieved by integrating the viral genome into the cell genome or by expressing viral proteins that equally segregate the viral genome into daughter cells during cell partitioning. The net balance between virus and host preserve the integrity of both. Cell transformation is probably not an evolutionary viral strategy, but rather a biological accident that rarely occurs in the virus-host interaction. All virus-associated tumours result from the cooperation of various events, involving more than persistent infection and viral transformation mechanisms.
Infection as a causal factor of cancer
2012
By 2030 nearly one in five of all new cases of cancer in the world, and nearly one in six cancer deaths, will occur in Commonwealth member states (Ferley et al., 2010). Projections of the International Agency for Research on Cancer (IARC) indicate that the number of new cases of cancer in the Commonwealth will rise by more than 77 per cent – from 2,263,427 to 4,003,875 – and cancer deaths by more than 81 per cent – from 1,455,050 to 2,592,240 (ibid.). Lowand middle-income member states, particularly those in South Asia, will bear the brunt of this unfolding cancer pandemic where it is estimated that the number of new cancer cases will rise by 72 per cent and cancer deaths by more than 80 per cent (ibid.). Only effective prevention can reduce the incidence of cancer. A first step towards this is an understanding of the factors that predispose to cancer. These factors differ, often quite markedly, between the more and less developed countries and across different geographical regions....
Cancer Epidemiology Biomarkers & Prevention
Various estimates of the proportion of all cancers attributable to infections have been proposed but none have been numerically justified. We have reviewed the evidence for "causality" with respect to infectious agents linked with cancer and estimated the fraction of all cancer cases concerned that are aUributable to it. The etiological fraction was applied to the estimated annual incidence of cancer at each specific site in 1990, and the number of attributable cases was obtained. We estimate that 15.6% (1,450,000 cases) of the worldwide incidence of cancer in 1990 can be attributed to infection with either the hepatitis B and C viruses, the human papillomaviruses, EBV, human T-cell lymphotrophic virus I, HIV, the bacterium Helicobacter pylon, schistosomes, or liver flukes. There would be 21% fewer cases of cancer in developing countries (1,000,000 fewer cases per year) and 9% fewer cases in developed countries (375,000 fewer cases per year) if these infectious diseases were prevented. The attributable fraction at the specific sites varies from 89% of cervix cancers attributable to the papillomaviruses to 1 % of all leukemias attributable to human T-cell lymphotrophic virus I.
Cancers Attributable to Infectious Agents: an Ecological Study in Asia
Asian Pacific Journal of Environment and Cancer
Infections are a major contributor to cancer, especially in developing countries. Infections through the virus, bacteria and parasites are the most and most preventable causes of cancer in the world. The aim of the current study was to investigate the epidemiology of cancer-related infections in Asia. We considered 4 infectious agents classified as carcinogenic to human beings by the International Agency for Research on Cancer. We calculated the number of new cancer cases in 2012 attributable to infections by country, by combining cancer incidence estimates (from GLOBOCAN 2012) with the estimates of attributable fraction (AF) for the infectious agents. AF estimates were calculated from the prevalence of infection in cancer cases for the infection (for some sites). According to data registered in 2012, about 14 million new cases of cancer were detected worldwide of which 2. 2 million people (15.4%) diagnosed with cancer due to infection. The highest incidence of infectious cancers re...