Detection of Epstein–Barr virus in breast carcinoma in Egyptian women
Introduction
Epstein–Barr virus (EBV) is a ubiquitous DNA virus of the herpes family that infects > 90% of humans and is usually carried lifelong as an asymptomatic infection. It is the causative agent of infectious mononucleosis (IM) and has been associated with a growing list of malignancies of both lymphoid and epithelial origin including Burkitt's lymphoma, B-cell lymphoma in immunocompromised, Hodgkin's lymphoma, and nasopharyngeal carcinoma (NPC). Based on this association, the WHO International Agency for Research on Cancer (IARC) has classified EBV among group I carcinogens which are agents that definitely cause neoplasm in humans [1], [2].
Over the past decade several investigators have raised the possibility that EBV may also be involved in the pathogenesis of breast carcinoma (BC), the most common carcinoma in females [3].
Early studies addressing this issue focused on medullary carcinomas since these are morphologically similar to NPC. However, these studies consistently failed to detect EBV using various techniques [4], [5]. The possibility that invasive ductal and invasive lobular BC might be EBV-associated was raised by Labrecque et al. [6], triggering a large number of follow up studies. However, this association has been constantly debated and the results of different studies are controversial [3]. Proof beyond a reasonable doubt that EBV had anything to do with the development of BC requires substantial additional evidence, that can only be obtained through further research.
In addition, various characteristics make the association of EBV with BC deserves to be further studied. First, IM affects mainly the teenagers, a period of strong proliferation of the mammary glands in girls [7]. Second, in vitro, mammary epithelial cells can be infected by direct contact with lymphoblastoid cellular lines infected by EBV [8]. Third, the transfection of subfragment of EBV-DNA stimulates the growth of normal human breast epithelial cells [9]. Fourth, BC has epidemiologic similarities with young adulthood Hodgkin's disease (YAHD) that has an established causal association with EBV [10]. Fifth, EBV has been identified in benign tumors of the breast among immunosuppressed females [11]. Sixth, in vitro, EBV-infected cells are resistant to paclitaxel (taxol), a chemotherapy commonly used in the treatment of BC, and the virus provokes overexpression of a multidrug resistance gene (MDR1) [12]. Finally, immunotherapeutic and antiviral strategies are currently being developed for the treatment of EBV-positive Hodgkin's lymphoma and NPC [13], [14], and they could potentially also be applied to EBV-associated BC.
Based on these considerations and in view of the high incidence of female BC in Egypt [15] this association required clarification as it could profoundly shape the clinical diagnosis, disease management and, potentially, patient outcome.
Before undertaking this study, it was important to establish criteria for the definition of EBV-associated tumors. PCR is a method potentially very significant and specific to detect EBV-DNA, however, it leaves unanswered the question of the cellular source of any viral genomes detected [16]. It has been strongly argued that infiltrating EBV-infected lymphocytes might explain the presence of EBV in breast tumors [17]. Unequivocal localization of the virus is best achieved by in situ techniques [18]. Immunohistochemical methods are available for the detection of viral proteins in paraffin sections. However, some of these proteins are not consistently expressed in latent EBV infection. Only EBV nuclear antigen-1 (EBNA-1) is expressed in all known forms of viral latency and in all EBV-associated malignancies. EBNA-1 is required for viral DNA replication and the maintenance of the EBV episome in infected cells. Therefore it is considered to be a good marker for the presence of the virus [19]. Thus we aimed in this work to assess the association of EBV with BC in Egyptian females employing a combination of two methods; screening for the presence of EBV by both EBNA-1 immunostaining and by PCR for EBV-DNA detection.
Section snippets
Subjects and methods
This is a prospective study that included a total number of 60 female patients who were classified into 2 groups; group with BC (40 patients) and a control group (20 patients).
Results
This study included 60 female patients divided into 2 groups, BC group; (40 patients) with primary unilateral invasive BC with no other primary cancer and 20 age matched females with fibrocystic disease of breast as a control group.
Different clinical characteristics of the patients with BC, histopathologic types of the tumors and association with the presence of EBV-DNA as determined by PCR, are reported in Table 2.
Discussion
Over the past decade, the EBV association with BC has been constantly debated despite the well-documented presence of EBV genetic material in up to 51% of breast tumors. This controversy is due to the failure of some investigators to identify EBV in BC [3]. This might be due in part to epidemiological variation in EBV infections, like difference in the age at which the studied patients had acquired primary EBV infection; as populations with higher incidence rates of BC correspond to those with
Acknowledgment
The authors thank Dr. Samar K. Kassim, Oncology Diagnostic Unit, Biochemistry Department, Faculty of Medicine, Ain Shams University, Cairo, Egypt, for generously providing the positive control.
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