Mouse mammary tumor virus-like sequences in human breast cancer

The association between infectious agents and breast cancer: a review of the epidemiologic evidence

PURPOSE

Several viruses have been casually linked to human cancers, including cervical, nasopharyngeal, liver, sarcoma, and Merkel cell carcinomas. However, the etiologic contribution of viral infections to breast cancer, the number one incident cancer among women worldwide, is not well established. Among studies exploring associations of viruses with breast cancer, potential linkages have been identified between breast cancer and five viruses: beta retrovirus, (i.e., mouse mammary tumor virus), human papillomavirus, Epstein Barr virus. bovine leukemia virus, and human cytomegalovirus.

METHODS

In this review, we provide a comprehensive evaluation of epidemiological ecologic, case-control, case-only, and cohort studies investigating these associations. We discuss results from several existing reviews and meta-analyses, evaluate epidemiological studies published in the past five years, and assess the relationship between these viruses and breast tumor clinicopathological factors.

RESULTS

The strongest epidemiological evidence for a viral role in breast cancer exists for MMTV and HPV, though limitations include lack of prospective studies for MMTV and potential detection bias in HPV studies. Viral detection challenges have limited studies of EBV and HCMV. Fewer studies have evaluated BLV, and though it has been associated with higher risk of breast cancer, sample sizes are quite small.   CONCLUSION: While epidemiologic evidence exists for an association between these five viruses and breast cancer, various methodological issues and lack of prospective studies preclude robust conclusions. Future research should prioritize establishing a temporal relationship between infection and disease, minimizing misclassification of detection assays, and further exploring the influence of co-infections.

Special Issue "Human Betaretrovirus and Related Diseases"

A betaretrovirus resembling mouse mammary tumor virus (MMTV) was first linked with human breast cancer over 50 years ago [...]

Life after Cleavage: The Story of a β-Retroviral (MMTV) Signal Peptide-From Murine Lymphoma to Human Breast Cancer

An increasing body of evidence in recent years supports an association of the betaretrovirus mouse mammary tumor virus (MMTV) with human breast cancer. This is an issue that still raises heated controversy. We have come to address this association using the signal peptide p14 of the MMTV envelope precursor protein as a key element of our strategy. In addition to its signal peptide function, p14 has some significant post endoplasmic reticulum (ER)-targeting characteristics: (1) it localizes to nucleoli where it binds key proteins (RPL5 and B23) involved (among other activities) in the regulation of nucleolar stress response, ribosome biogenesis and p53 stabilization; (2) p14 is a nuclear export factor; (3) it is expressed on the cell surface of infected cells, and as such, is amenable to, and successfully used, in preventive vaccination against experimental tumors that harbor MMTV; (4) the growth of such tumors is impaired in vivo using a combination of monoclonal anti-p14 antibodies or adoptive T-cell transfer treatments; (5) p14 is a phospho-protein endogenously phosphorylated by two different serine kinases. The phosphorylation status of the two sites determines whether p14 will function in an oncogenic or tumor-suppressing capacity; (6) transcriptional activation of genes (RPL5, ErbB4) correlates with the oncogenic potential of MMTV; (7) finally, polyclonal anti-p14 antibodies have been applied in immune histochemistry analyses of breast cancer cases using formalin fixed paraffin-embedded sections, supporting the associations of MMTV with the disease. Taken together, the above findings constitute a road map towards the diagnosis and possible prevention and treatment of MMTV-associated breast cancer.

Isolation of a Human Betaretrovirus from Patients with Primary Biliary Cholangitis

A human betaretrovirus (HBRV) has been linked with the autoimmune liver disease, primary biliary cholangitis (PBC), and various cancers, including breast cancer and lymphoma. HBRV is closely related to the mouse mammary tumor virus, and represents the only exogenous betaretrovirus characterized in humans to date. Evidence of infection in patients with PBC has been demonstrated through the identification of proviral integration sites in lymphoid tissue, the major reservoir of infection, as well as biliary epithelium, which is the site of the disease process. Accordingly, we tested the hypothesis that patients with PBC harbor a transmissible betaretrovirus by co-cultivation of PBC patients’ lymph node homogenates with the HS578T breast cancer line. Because of the low level of HBRV replication, betaretrovirus producing cells were subcloned to optimize viral isolation and production. Evidence of infection was provided by electron microscopy, RT-PCR, in situ hybridization, cloning of the HBRV proviral genome and demonstration of more than 3400 integration sites. Further evidence of viral transmissibility was demonstrated by infection of biliary epithelial cells. While HBRV did not show a preference for integration proximal to specific genomic features, analyses of common insertion sites revealed evidence of integration proximal to cancer associated genes. These studies demonstrate the isolation of HBRV with features similar to mouse mammary tumor virus and confirm that patients with PBC display evidence of a transmissible viral infection.

Mouse Mammary Tumour Virus (MMTV) in Human Breast Cancer—The Value of Bradford Hill Criteria

For many decades, the betaretrovirus, mouse mammary tumour virus (MMTV), has been a causal suspect for human breast cancer. In recent years, substantial new evidence has been developed. Based on this evidence, we hypothesise that MMTV has a causal role. We have used an extended version of the classic A. Bradford Hill causal criteria to assess the evidence. 1. Identification of MMTV in human breast cancers: The MMTV 9.9 kb genome in breast cancer cells has been identified. The MMTV genome in human breast cancer is up to 98% identical to MMTV in mice. 2. Epidemiology: The prevalence of MMTV positive human breast cancer is about 35 to 40% of breast cancers in Western countries and 15 to 20% in China and Japan. 3. Strength of the association between MMTV and human breast cancer: Consistency—MMTV env gene sequences are consistently five-fold higher in human breast cancer as compared to benign and normal breast controls. 4. Temporality (timing) of the association: MMTV has been identified in benign and normal breast tissues up to 10 years before the development of MMTV positive breast cancer in the same patient. 5. Exposure: Exposure of humans to MMTV leads to development of MMTV positive human breast cancer. 6. Experimental evidence: MMTVs can infect human breast cells in culture; MMTV proteins are capable of malignantly transforming normal human breast epithelial cells; MMTV is a likely cause of biliary cirrhosis, which suggests a link between MMTV and the disease in humans. 7. Coherence—analogy: The life cycle and biology of MMTV in humans is almost the same as in experimental and feral mice. 8. MMTV Transmission: MMTV has been identified in human sputum and human milk. Cereals contaminated with mouse fecal material may transmit MMTV. These are potential means of transmission. 9. Biological plausibility: Retroviruses are the established cause of human cancers. Human T cell leukaemia virus type I (HTLV-1) causes adult T cell leukaemia, and human immunodeficiency virus infection (HIV) is associated with lymphoma and Kaposi sarcoma. 10. Oncogenic mechanisms: MMTV oncogenesis in humans probably differs from mice and may involve the enzyme APOBEC3B. Conclusion: In our view, the evidence is compelling that MMTV has a probable causal role in a subset of approximately 40% of human breast cancers.

Prevalence and characteristics of mouse mammary tumor virus-like virus associated breast cancer in China

BACKGROUND

Despite extensive molecular epidemiological studies, the prevalence and characteristics of Mouse Mammary Tumor Virus-Like Virus (MMTV-LV) in Chinese women breast cancer are still unclear. Besides, the prevalence of MMTV-LV in women breast cancer tissue varies in different countries and its dependent factors remain inconclusive.

METHODS

In the first part of the study, a case-control study was performed. 119 breast cancer samples (84 from Northern China and 35 from Southern China) and 50 breast fibroadenoma specimens were collected from Chinese women patients. MMTV-like env sequence and the homology to MMTV env gene were analysed by semi-nested polymerase chain reaction (PCR). We also explored the association of MMTV-LV prevalence with sample sources (Southern and Northern China) and patients' clinicopathological characteristics. To investigate the dependent factors of the prevalence of MMTV-LV in breast cancer worldwide, a meta-analysis was conducted in the second part of the study.

RESULTS

We found that the prevalence of MMTV-LV was much higher in breast cancer tissues (17.65%) than that in breast fibroadenoma specimens (4.00%) (P < 0.05). MMTV-LV prevalence in Chinese women breast cancer tissues was significantly different between Southern China (5.71%) and Northern China (22.62%) (P < 0.05). The prevalence of MMTV-LV also associates significantly with expression of HER2, but shows no significant correlation with other parameters. In the meta-analysis, we found that MMTV-LV prevalence in breast cancer tissue was dependent on the distribution of M. domesticus mouse (M. d), M. musculus mouse (M.m) and M.castaneus mouse (M.c) worldwide (P < 0.05).

CONCLUSION

The distribution of house mice may be a crucial environmental factor that explains the geographic differences in human breast cancer incidence. Our findings may provide a potential avenue of prevention, diagnosis and treatment for breast cancer.

Catching viral breast cancer

Abstract

We have considered viruses and their contribution to breast cancer.

Mouse mammary tumour virus

The prevalence of mouse mammary tumour virus (MMTV) is 15-fold higher in human breast cancer than in normal and benign human breast tissue controls. Saliva is the most plausible means of transmission. MMTV has been identified in dogs, cats, monkeys, mice and rats. The causal mechanisms include insertional oncogenesis and mutations in the protective enzyme ABOBEC3B.

Human papilloma virus

The prevalence of high risk human papilloma viruses (HPV) is frequently six fold higher in breast cancer than in normal and benign breast tissue controls. Women who develop HPV associated cervical cancer are at higher than normal risk of developing HPV associated breast cancer. Koilocytes have been identified in breast cancers which is an indication of HPV oncogenicity. The causal mechanisms of HPVs in breast cancer appear to differ from cervical cancer. Sexual activity is the most common form of HPV transmission. HPVs are probably transmitted from the cervix to the breast by circulating extra cellular vesicles.

Epstein Barr virus

The prevalence of Epstein Barr virus (EBV) is five fold higher in breast cancer than in normal and benign breast tissue controls. EBV is mostly transmitted from person to person via saliva. EBV infection predisposes breast epithelial cells to malignant transformation through activation of HER2/HER3 signalling cascades. EBV EBNA genes contribute to tumour growth and metastasis and have the ability to affect the mesenchymal transition of cells.

Bovine leukemia virus

Bovine leukemia virus (BLV) infects beef and dairy cattle and leads to various cancers. The prevalence of BLV is double in human breast cancers compared to controls. Breast cancer is more prevalent in red meat eating and cow’s milk consuming populations. BLV may be transmitted to humans from cattle by the consumption of red meat and cow’s milk.

Conclusion

The evidence that MMTV, high risk HPVs and EBVs have causal roles in human breast cancer is compelling. The evidence with respect to BLV is more limited but it is likely to also have a causal role in human breast cancer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13027-021-00366-3.

Prevalence of MMTV-Like env Sequences and Its Association with BRCA1/2 Genes Mutations Among Egyptian Breast Cancer Patients

Background

Mouse mammary tumor virus (MMTV) is thought to have a role in human breast cancer (BC) pathogenesis. BRCA1 and 2 genes mutations are well-established risk factors for BC. The purpose of this study was to evaluate the presence of MMTV in familial and non-familial Egyptian breast cancer patients. We also aimed to establish a correlation between BRCAs genes mutations and MMTV infection in those patients.

Patients and Methods

The study was included 80 BC patients and 10 healthy women were included as a control group. We used PCR to amplify a 250-bp MMTV-like env sequence. We also used PCR followed by direct sequencing to identify the genetic variation of exons 2, 13, 19 of BRCA1 gene and exon 9 and region f of exon 11 of BRCA2 gene. High resolution melting (HRM) analysis was used to screen the selected exons of BRCA1/2 genes in order to detect different variants.

Results

MMTV DNA-like env sequences were detected in 70%, 76% of familial and non-familial BC patients, respectively, and it was not detected in any of the control subjects. The presence of viral sequences was associated with larger tumor size in the sporadic patients. Seventy BC patients showed variations in BRCA1/2 genes according to HRM analysis and sequencing analysis showed two different sequences of polymorphism among 22 familial and non-familial BC patients.

Conclusion

MMTV DNA was present among BC patients and it was associated with increased tumor growth. This indicates a potential role for MMTV in BC patients with and without deleterious mutation in BRCA1/2 genes.

Evidence for a causal role by mouse mammary tumour-like virus in human breast cancer

We have reviewed the evidence relevant to mouse mammary tumour viruses (MMTV) and human breast cancer. The prevalence of MMTV- like gene sequences is 15-fold higher in human breast cancer than in normal human breast tissue controls and is present in up to 40% of human breast cancers. MMTV-like gene sequences can be identified in benign breast tissues 1-11 years before the development of positive MMTV-like breast cancer in the same women. The prevalence of MMTV antibodies in sera from women with breast cancer is 5-fold higher than in normal women. MMTV can infect human breast epithelial cells and integrate at random into the human genome located in those cells. MMTV-like gene sequences are present in human milk from normal lactating women and with increased prevalence in milk from women at risk of breast cancer. MMTV-like virus associated human breast cancer has strikingly similar features to MMTV-associated mouse mammary tumours. These features include almost identical nucleotide sequences and structure of the MMTV genome, histology, superantigen expression, MMTV infection of B and T lymphocytes and hormone dependence. MMTV-like gene sequences have also been identified in dogs, cats, monkeys, mice and rats. Saliva has been identified as the most plausible means of transmission from human to human and possibly from dogs to humans. The evidence meets the classic causal criteria. A causal role for MMTV-like viruses in human breast cancer is highly likely.

Characterization of an integrated, endogenous mouse mammary tumor virus-like (MMTV) betaretrovirus genome in a black Syrian hamster (Mesocricetus auratus)

Retroviruses (family Retroviridae) are important agents of humans and animals. This study reports the detection and complete genome characterization of a novel endogenous retrovirus from the black Syrian hamster (Mesocricetus auratus) with a squamous cell skin tumor. The proviral genome, tentatively named black Syrian hamster retrovirus (BSHRV/2013/HUN, MK304634), was 8784 nucleotide in length with typical full-length betaretrovirus genome organization of 5'LTR-gag-pro-pol-env-3'LTR and with a characteristic mouse mammary tumor virus-like (MMTV) betaretrovirus dUTPase domain but without a sag gene. The BSHRV gag (534aa), pro/pol (~1099aa) and env (672aa) proteins had 56%/63%/50% aa identity to the corresponding proteins of MMTV (AF228552). The proviral DNA is detectable in tumor as well as in tumor-free cells by conventional PCR and qPCR but only visible in the tumor cells by in situ hybridization. Low level retroviral RNA expression was found only in the DNase-treated RNA tumor samples using RT/nested PCR. BSHRV/2013/HUN-like betaretrovirus DNA was also identified from a faecal and tissue samples from 1 of the further 3 tested individuals by nested-PCR and qPCR. Further research is needed to investigate the distribution, activity and etiological role of this novel MMTV-like betaretrovirus species in hamster.

Involvement of a mouse mammary tumor virus (MMTV) homologue in human breast cancer: Evidence for, against and possible causes of controversies

Breast cancer (BC) is a complex and heterogeneous disease whose evolution depends on the tumor-host interaction. This type of cancer occurs when the mammary cells begin to grow wildly and become able to invade nearby tissues and/or promote metastases. Mouse mammary tumor virus (MMTV) is the accepted etiological agent of mammary tumors in mice. The identification of MMTV-like sequences and antigens in human mammary carcinoma has supported the theory that a virus homologous to MMTV (namely, HMTV) may be involved in human BC, but the role of retroviral elements in this disease remains elusive, as results from different research groups were contradictory. In the present review we present works for and against the involvement of HMTV in BC and discuss possible causes of divergences among studies. In the final section we fit current data regarding this issue to stablished causality criteria. We conclude that there is convincing data supporting the association of HMTV with BC, however there is still a need for epidemiological and basic research studies focusing on carcinogenic mechanisms for this virus in humans to fully understand its role in BC. This knowledge may open the way for the development of new preventive and therapeutic approaches in human BC.

Association of Mouse Mammary Tumor Virus With Human Breast Cancer: Histology, Immunohistochemistry and Polymerase Chain Reaction Analyses

Purpose

The purpose of this study is to determine whether mouse mammary tumor virus (MMTV)-associated human breast cancer has the same or similar histology to MMTV-associated mouse mammary tumors. Such associations may indicate a role for MMTV in human breast cancer.

Methods

Immunohistochemical techniques (using antibodies directed against the signal peptide p14 of the envelope precursor protein of MMTV) and polymerase chain reaction (PCR) analyses were used to identify MMTV proteins and MMTV-like envelope gene sequences in a series of breast cancers from Australian women. The histological characteristics of these human breast cancer specimens were compared with MMTV positive mouse mammary tumors. The same methods were used to study benign breast tissues which 1–11 years later developed into breast cancer.

Results

MMTV p14 proteins were identified in 27 (54%) of 50 human breast cancers. MMTV env gene sequences were identified by PCR in 12 (27%) of 45 human breast cancers. There was a significant correlation between the presence of MMTV (identified by p14 immunohistochemistry) in human breast cancers and histological characteristics similar to MMTV positive mouse mammary tumors (p = 0.001). There was a non-significant correlation between the presence of MMTV env gene sequences (identified by PCR) in human breast cancers and histological characteristics similar to MMTV positive mouse mammary tumors (p = 0.290). MMTV p14 proteins were identified in 7 (54%) of 13 benign breast specimens that later developed into human breast cancers. MMTV by PCR was identified in two benign specimens one of whom later developed MMTV positive breast cancer.

Discussion

These observations offer evidence that MMTV may be associated with characteristic human breast cancer histology. p14-based immunohistochemistry appears to be a more reliable technique than PCR for the identification of MMTV in human breast cancer. Identification of MMTV-associated p14 proteins in benign breast tissues confirms prior PCR-based studies that MMTV infection occurs before the development of MMTV positive breast cancer.

Conclusion

Many MMTV positive human breast cancers have similar histology to MMTV positive mouse mammary tumors. MMTV infection identified in benign breast tissues precedes development of MMTV positive human breast cancer. When considered in the context of prior studies, these observations indicate a likely role for MMTV in human breast cancer.

Viral infections and breast cancer - A current perspective

Sporadic human breast cancer is the most common cancer to afflict women. Since the discovery, decades ago, of the oncogenic mouse mammary tumour virus, there has been significant interest in the potential aetiologic role of infectious agents in sporadic human breast cancer. To address this, many studies have examined the presence of viruses (e.g. papillomaviruses, herpes viruses and retroviruses), endogenous retroviruses and more recently, microbes, as a means of implicating them in the aetiology of human breast cancer. Such studies have generated conflicting experimental and clinical reports of the role of infection in breast cancer. This review evaluates the current evidence for a productive oncogenic viral infection in human breast cancer, with a focus on the integration of sensitive and specific next generation sequencing technologies with pathogen discovery. Collectively, the majority of the recent literature using the more powerful next generation sequencing technologies fail to support an oncogenic viral infection being involved in disease causality in breast cancer. In balance, the weight of the current experimental evidence supports the conclusion that viral infection is unlikely to play a significant role in the aetiology of breast cancer.

Prevalence of Mouse Mammary Tumor Virus (MMTV)-like sequences in human breast cancer tissues and adjacent normal breast tissues in Saudi Arabia

BACKGROUND

Breast cancer is considered the most common cancer in women worldwide and is the leading cause of cancer mortality. Sequences similar to Mouse Mammary Tumor Virus (MMTV) were detected in human breast cancer in several studies from different geographical areas. However, the role played by this virus in breast cancer tumorigenesis is not completely understood. These MMTV-like sequences were found to be associated with breast cancer of more malignant types. The aim of this study is to determine the prevalence of MMTV-like envelope gene (env) positivity in breast cancer and non-cancerous breast tissue from Saudi Arabia.

METHODS

Detection of MMTV-like env proviral sequences was done using newly designed primers for conventional polymerase chain reaction (PCR). One hundred nighty four samples were collected from 103 females with breast cancer in addition to 51 control breast tissue obtained from individuals without cancer. We additionally investigated the association of proviral positivity with age of the patients, grade of breast cancer and presence of lymph node metastasis. The results were confirmed by sequencing.

RESULTS

The prevalence of MMTV-like env proviral positivity was 8.7% (9/103). MMTV env proviral sequences were detected in 5.9% (6/101) of breast cancer tissues and 9.7% (9/93) of non-cancerous adjacent tissues obtained from the same patients. None of the 51 control sample showed positive result for the MMTV env gene. No significant association was found between detection of the virus and the age of the patient, grade of the cancer or presence of metastasis.

CONCLUSION

We document the presence of low frequency of MMTV env provirus sequence among breast cancer patients from Saudi Arabia. Further studies are needed to explore the role of the MMTV in breast cancer.

Oncogenic Viruses and Breast Cancer: Mouse Mammary Tumor Virus (MMTV), Bovine Leukemia Virus (BLV), Human Papilloma Virus (HPV), and Epstein-Barr Virus (EBV)

Background

Although the risk factors for breast cancer are well established, namely female gender, early menarche and late menopause plus the protective influence of early pregnancy, the underlying causes of breast cancer remain unknown. The development of substantial recent evidence indicates that a handful of viruses may have a role in breast cancer. These viruses are mouse mammary tumor virus (MMTV), bovine leukemia virus (BLV), human papilloma viruses (HPVs), and Epstein–Barr virus (EBV-also known as human herpes virus type 4). Each of these viruses has documented oncogenic potential. The aim of this review is to inform the scientific and general community about this recent evidence.

The evidence

MMTV and human breast cancer—the evidence is detailed and comprehensive but cannot be regarded as conclusive. BLV and human breast cancer—the evidence is limited. However, in view of the emerging information about BLV in human breast cancer, it is prudent to encourage the elimination of BLV in cattle, particularly in the dairy industry. HPVs and breast cancer—the evidence is substantial but not conclusive. The availability of effective preventive vaccines is a major advantage and their use should be encouraged. EBV and breast cancer—the evidence is also substantial but not conclusive. Currently, there are no practical means of either prevention or treatment. Although there is evidence of genetic predisposition, and cancer in general is a culmination of events, there is no evidence that inherited genetic traits are causal.

Conclusion

The influence of oncogenic viruses is currently the major plausible hypothesis for a direct cause of human breast cancer.

Multiple oncogenic viruses are present in human breast tissues before development of virus associated breast cancer

Background

Multiple oncogenic viruses including, mouse mammary tumor virus, bovine leukemia virus, human papilloma virus, and Epstein Barr virus, have been identified as separate infectious pathogens in human breast cancer. Here we demonstrate that these four viruses may be present in normal and benign breast tissues 1 to 11 years before the development of same virus breast cancer in the same patients.

Methods

We combined the data we developed during investigations of the individual four oncogenic viruses and breast cancer. Patients who had benign breast biopsies 1–11 years prior to developing breast cancer were identified by pathology reports from a large Australian pathology service (Douglas Hanly Moir Pathology). Archival formalin fixed specimens from these patients were collected. The same archival specimens were used for (i) investigations of mouse mammary tumour virus (also known as human mammary tumour virus) conducted at the Icahn School of Medicine at Mount Sinai, New York and at the University of Pisa, Italy, (ii) bovine leukemia virus conducted at the University of California at Berkeley,(iii) human papilloma virus and Epstein Barr virus conducted at the University of New South Wales, Sydney, Australia.

Seventeen normal breast tissues from cosmetic breast surgery conducted on Australian patients were used as controls. These patients were younger than those with benign and later breast cancer.

Results

Standard and in situ polymerase chain reaction (PCR) methods were used to identify the four viruses. The detailed methods are outlined in the separate publications.: mouse mammary tumor virus, human papilloma virus and Epstein Barr virus (Infect Agent Cancer 12:1, 2017, PLoS One 12:e0179367, 2017, Front Oncol 5:277, 2015, PLoS One 7:e48788, 2012).

Epstein Barr virus and human papilloma virus were identified in the same breast cancer cells by in situ PCR.

Mouse mammary tumour virus was identified in 6 (24%) of 25 benign breast specimens and in 9 (36%) of 25 breast cancer specimens which subsequently developed in the same patients.

Bovine leukemia virus was identified in 18 (78%) of 23 benign breast specimens and in 20 (91%) of 22 subsequent breast cancers in the same patients.

High risk human papilloma viruses were identified in 13 (72%) of 17 benign breast specimens and in 13 (76%) of 17 subsequent breast cancers in the same patients.

Epstein Barr virus was not identified in any benign breast specimens but was identified in 3 (25%) of 12 subsequent breast cancers in the same patients.

Mouse mammary tumour virus 3 (18%), bovine leukemia virus 6 (35%), high risk human papilloma virus 3 (18%) and Epstein Barr virus 5 (29%) were identified in 17 normal control breast specimens.

Conclusions

These findings add to the evidence that multiple oncogenic viruses have potential roles in human breast cancer. This is an important observation because evidence of prior infection before the development of disease is a key criterion when assessing causation.

Prevalence of EBV, HPV and MMTV in Pakistani breast cancer patients: A possible etiological role of viruses in breast cancer

BACKGROUND

Breast cancer being a multifactorial disease, the role of infectious agent in development of disease is of great interest. The high incidence of breast cancer around the world has woken the interest in a viral etiology of breast cancer. Despite decades of research, no etiologic factor(s) for human breast cancer has been known and the quest for a contributing cause has all but been abandoned during the past years. Recent investigations have linked breast cancer to viral infections, such as Epstein-Barr virus (EBV), Human papillomavirus (HPV) and mouse mammary tumor virus.

AIM

To investigate the possible association of EBV, HPV and MMTV infection with breast cancer development and progression.

METHODS

Screening of isolated genomic DNA from FFPE breast cancer tissue biopsies (n=250) using standard polymerase chain reaction and correlation of virus prevalence with BC disease outcomes using statistical analysis software (SPSS 16.0).

RESULTS

Our findings suggest the prevalence of EBV (24.4%), HPV (18.1%) and MMTV (29.3%), while coinfection of HPV and EBV was detected in 9.2% (23/250), co infection of HPV and MMTV in 3.2% (8/250) and coinfection of EBV and MMTV in 6% (15/250) of breast cancer samples. No virus was detected in 59.5% of the breast cancer samples. Mono infection of EBV and HPV do not statistically co-relate with the clinico-pathological outcomes of breast cancer disease, though MMTV infection does co-relate with age and grade of breast cancer disease. In our study, the prevalence of coinfection of HPV, EBV and MMTV in Pakistani breast cancer patients is rare, still there is a possibility of synergistic carcinogenic effect of different viruses in the development of breast cancer disease.

CONCLUSION

The significant percentage of virus prevalence shows potential role in breast cancer development. However, this study provides substantial but not conclusive evidence for the involvement of viruses in BC disease development and progressiveness.

Mouse mammary tumour virus (MMTV) and human breast cancer with neuroendocrine differentiation

Background

Mouse mammary tumour viruses (MMTVs) may have a role in a subset of human breast cancers. MMTV positive human breast cancers have similar histological characteristics to neuroendocrine breast cancers and to MMTV positive mouse mammary tumours. The purpose of this study was to investigate the expression of neuroendocrine biomarkers – synaptophysin and chromogranin, to determine if these histological characteristics and biomarker expression were due to the influences of MMTV.

Methods

Immunohistochemistry analyses to identify synaptophysin and chromogranin were conducted on a series of human breast cancers in which (i) MMTV had been previously identified and had similar histological characteristics to MMTV positive mouse mammary tumours and (ii) MMTV positive mouse mammary tumours.

Results

The expression of synaptophysin and chromogranin in MMTV positive mouse mammary tumors were all positive (7 of 7 specimens – 100% positive). The expression of synaptophysin and chromogranin in MMTV positive human breast cancers was much less prevalent (3 of 22 – 14%). There was no expression of synaptophysin and chromogranin in the normal breast tissue control specimens.

Discussion

It is not possible to draw any firm conclusions from these observations. However, despite the small numbers of MMTV positive mouse mammary tumours in this study, the universal expression in these specimens of synaptophysin and chromogranin proteins is striking. This pattern of synaptophysin and chromogranin expression is very different from their expression in MMTV positive human breast cancers. The reason for these differences is not known.

Conclusions

The high prevalence of positive expression of synaptophysin and chromogranin in MMTV positive mouse mammary tumours and low expression of synaptophysin and chromogranin in MMTV positive human breast cancers indicates that MMTV is not usually associated with neuroendocrine human breast cancers.

Electronic supplementary material

The online version of this article (doi:10.1186/s13027-017-0135-8) contains supplementary material, which is available to authorized users.

Lessons Learned from Mouse Mammary Tumor Virus in Animal Models

Mouse mammary tumor virus (MMTV), which was discovered as a milk-transmitted, infectious, cancer-inducing agent in the 1930s, has been used as an animal model for the study of retroviral infection and transmission, antiviral immune responses, and breast cancer and lymphoma biology. The main target cells for MMTV infection in vivo are cells of the immune system and mammary epithelial cells. Although the host mounts an immune response to the virus, MMTV has evolved multiple means of evading this response. MMTV causes mammary tumors when the provirus integrates into the mammary epithelial and lymphoid cell genome during viral replication and thereby activates cellular oncogene expression. Thus, tumor induction is a by-product of the infection cycle. A number of important oncogenes have been discovered by carrying out MMTV integration site analysis, some of which may play a role in human breast cancer.

Mouse mammary tumor-like virus (MMTV) is present in human breast tissue before development of virally associated breast cancer

Background

There is substantial evidence that a virus homologous to mouse mammary tumor virus (MMTV) may have a role in human breast cancer. The present study indicates that those who developed breast cancer associated with an MMTV-like virus had this virus in their non-cancerous breast tissues years before the cancer developed.

Methods

Polymerase chain reaction (PCR) techniques and sequencing were used to identify MMTV-like envelope gene sequences (MMTV-like env sequences) in Australian benign breast biopsy specimens from women who several years later developed breast cancer. Murine contamination was excluded by stringent laboratory procedures, and the absence of intracisternal A particle sequences and mitochondrial cyclooxygenase sequences.

Results

MMTV-like env sequences (also called HMTV sequences to denote their source) were found in 9 of 25 breast cancer specimens (36%). Among 25 non-cancerous breast biopsies of these same patients taken 1 to 11 years earlier, six contained MMTV-like sequences (24%). Five of the six were among the nine virally-associated breast cancers. In two pairs of specimens, benign and malignant, env sequences were 97% identical.

Conclusions

The identification of MMTV (MMTV-like) sequences in breast tissues prior to the development of MMTV positive breast cancer fulfills a key criterion for a possible causal role for the MMTV-like virus in human breast cancer.

BST-2: at the crossroads of viral pathogenesis and oncogenesis

BST-2 is a moonlight protein with several protective and deleterious functions. Regulation of virus restriction and tumor aggressiveness are the most studied aspects of BST-2 function and thus, the main focus of this perspective. Virus inhibition roles of BST-2 have therapeutic potential that, if properly harnessed, could result in near broad spectrum antiviral. However, the involvement of BST-2 in cancer calls for additional studies on BST-2 biology and re-evaluation of the overall role of BST-2 in host protection, as it appears that BST-2 has pleiotropic effects in the host. Here, we analyze the antiviral and protumor roles of BST-2. We also discuss potential therapeutic options for BST-2 against viral infection and cancer.

Detection of MMTV-Like sequences in Moroccan breast cancer cases

Introduction

The mouse mammary tumor virus (MMTV) like sequences have been reported to be present in some human breast cancers, but their association with breast cancer development is still controversial.

Methods

In this retrospective study, we investigated the status of MMTV-like in 42 tumor biopsies and 18 paired normal tissues from Moroccan patients with breast cancer. MMTV-like env sequences were identified by PCR and confirmed by direct DNA sequencing.

Results

Specific MMTV-like env sequences were found in 24 (57.14%) cases of breast carcinomas, and 6 (33.3%) cases of matched normal breast tissues. Comparison to sociologic and clinicopathological parameters showed no significant association between the presence of MMTV-like sequences and age, menopausal status, histological subtype, histological grade, tumor size and the expression of hormone receptors (estrogen ER and/or progesterone PgR) and Her 2. However, a significant correlation was found between MMTV-like presence and parity (p = 0.024).

Conclusions

This present study confirms the presence of MMTV-like env sequences in breast cancer in Moroccan women, prompting further evaluation, on large sampling, to elucidate the probable causal roles of MMTV-like in breast cancer development.

Recent developments linking retroviruses to human breast cancer: infectious agent, enemy within or both?

Evidence is accumulating that one or more beta-retrovirus is associated with human breast cancer. Retroviruses can exist as an infectious (exogenous) virus or as a part of the genetic information of cells due to germline integration (endogenous). An exogenous virus with a genome that is highly homologous to mouse mammary tumour virus is gaining acceptance as possibly being associated with human breast cancer, and recently furnished evidence is discussed in this article, as is the evidence for involvement of an endogenous human beta-retrovirus, HERV-K. Modes of interaction are also reviewed and linkages to the APOBEC3 family are suggested.

Inflammatory breast cancer clusters: A hypothesis

Cancer clusters have long been a focus of interest because of the possibility of identifying etiologic agents. Only on rare occasions, however, have such cluster investigations been successful. One major difficulty in cluster investigations, particularly in the area of breast cancer, is the long latent period. There have been a number of publications providing a discouraging picture regarding cancer cluster investigations. The possibility of learning from a cluster investigation, however, is greatly increased if the cancer involved is relatively rare and if it has a short latent period. Inflammatory breast cancer (IBC) fits these criteria and is worth pursuing because of the strong evidence that environmental factors play a major role. In this report we describe our experience with several clusters and the lessons learned which are now being utilized to improve investigation of future IBC clusters. The first IBC cluster that we evaluated was in 2000, when we were asked to investigate an apparent cluster of IBC in Castro Valley, California where three women in an office setting of 24 people were diagnosed with IBC in a ten month period from May 1999 to March 2000. Our investigation of this striking cluster did not yield a specific trigger for this cluster but it did indicate that the women involved all had at least two IBC risk factors that may well have made them susceptible to getting IBC. We are now investigating another apparent cluster in Texas and are aware of several others requiring careful consideration. We see a need for a consistent protocol for the evaluation of IBC clusters focusing on the laboratory investigation of environmental triggers, primarily infectious agents and chemical carcinogens.

Human Mammary Tumor Virus (HMTV) sequences in human milk

Background

Retroviral sequences 90-95% homologous to the mouse mammary tumor virus (MMTV) were present in 38% of the breast cancers studied from American women and were not detectable in non-tumor breast tissue from the same patient. The entire proviral structure was described and viral particles were isolated from primary cultures of human breast cancer. This virus was designated as human mammary tumor virus (HMTV). Hormone response elements present in the HMTV Long-Terminal-Repeat (LTR) suggest a mechanism for association of HMTV with hormonally responding tissues. In fact, the incidence of HMTV sequences is higher in gestational breast cancers, which are associated with hormonal changes. Milk epithelial cells are also under hormonal regulation and therefore are excellent specimens for HMTV sequence detection.

Methods

The HMTV sequence was studied in milk samples from lactating women recruited with increased risk of breast cancer because they had undergone breast biopsies (Biopsy-Group) and lactating women without breast biopsies (Reference-Group).

Results

HMTV-env sequences were detected by PCR in milk of 7.61% of 92 women of the Reference-Group and in 20.55% of 73 women of the Biopsy-Group (p: 0.015). The sequences were 94-98% homologous to MMTV. HMTV-env and HMTV-env/LTR junction sequences were detected in high-speed pellet RNA, implying the presence of HMTV viral particles. PCR assays to detect the murine mitochondrial cytochrome oxidase gene and intracisternal-A-type particle sequences were performed to rule out mouse mitochondrial or genomic DNA contamination. Eight women of the 73 Biopsy-Group participants had breast cancer and the milk of only one of these eight women had HMTV-env sequences. In the remaining 65 women of the Biopsy-Group, under enough clinical suspicion to lead to biopsy, HMTV was detected in 14, nearly three times the number of milks as compared to the Reference-Group (21.54% versus 7.61%; p: 0.016).

Conclusion

The significance of HMTV in milk from the Reference-Group, the greater frequency in the milk of women who had undergone a breast biopsy and its possible infectivity for infants are important questions under study. The similarity of HMTV to MMTV is striking and suggests one possible avenue for viral transmission in humans.

Joint infectious causation of human cancers

Joint infectious causation of cancer has been accepted in a few well-studied instances, including Burkitt's lymphoma and liver cancer. In general, evidence for the involvement of parasitic agents in oncogenesis has expanded, and recent advances in the application of molecular techniques have revealed specific mechanisms by which host cells are transformed. Many parasites evolve to circumvent immune-mediated detection and destruction and to control critical aspects of host cell reproduction and survival: cell proliferation, apoptosis, adhesion, and immortalization. The host has evolved tight regulation of these cellular processes-the control of each represents a barrier to cancer. These barriers need to be compromised for oncogenesis to occur. The abrogation of a barrier is therefore referred to as an essential cause of cancer. Alternatively, some aspects of cellular regulation restrain but do not block oncogenesis. Relaxation of a restraint is therefore referred to as an exacerbating cause of cancer. In this chapter, we explore past and current evidence for joint infectious causation of cancer in the context of essential and exacerbating causes. We stress that discovery of joint infectious causation may provide great improvements in controlling cancer, particularly through the identification of many additional nonhuman targets for synergistic interventions for prevention and treatment.

Carcinogenic viruses and solid cancers without sufficient evidence of causal association

Viral infections are important risk factors for tumor development in humans. Selected types of cancers, either lymphomas or carcinomas, for which there is sufficient evidence in humans of a causal association with specific viruses, have been identified. Experimental and clinical data on the possible association of other tumor types and carcinogenic viruses are presently controversial. In this article, we review the current evidence on the relationship between breast, colorectal and lung cancers and carcinogenic viruses. The majority of the publications reviewed do not provide definitive evidence that the viruses studied are associated with breast, colon and lung cancers. However, since this association may be clinically relevant for some tumor subtypes (i.e., lung cancer and papillomaviruses), there is an urgent need for further investigation on this topic. Using innovative laboratory techniques for viral detection on well-defined tumor types, National and International networks against cancer should encourage and organize concerted research programs on viruses and solid cancer association.

Role of viruses in the development of breast cancer

The most common cancer worldwide among women is breast cancer. The initiation, promotion, and progression of this cancer result from both internal and external factors. The International Agency for Research on Cancer stated that 18-20% of cancers are linked to infection, and the list of definite, probable, and possible carcinogenic agents is growing each year. Among them, biological carcinogens play a significant role. In this review, data covering infection-associated breast and lung cancers are discussed and presented as possible involvements as pathogens in cancer. Because carcinogenesis is a multistep process with several contributing factors, we evaluated to what extent infection is significant, and concluded that members of the herpesvirus, polyomavirus, papillomavirus, and retrovirus families definitely associate with breast cancer. Detailed studies of viral mechanisms support this conclusion, but have presented problems with experimental settings. It is apparent that more effort needs to be devoted to assessing the role of these viruses in carcinogenesis, by characterizing additional confounding and synergistic effects of carcinogenic factors. We propose that preventing and treating infections may possibly stop or even eliminate certain types of cancers.

Aberrant DNA methylation of miR-219 promoter in long-term night shiftworkers

The idea that shiftwork may be carcinogenic in humans has gained widespread attention since the pioneering work linking shiftwork to breast cancer over two decades ago. However, the biomolecular consequences of long-term shiftwork exposure have not been fully explored. In this study, we performed a genome-wide CpG island methylation assay of microRNA (miRNA) promoters in long-term night shiftworkers and day workers. This analysis indicated that 50 CpG loci corresponding to 31 miRNAs were differentially methylated in night shiftworkers compared to day workers, including the circadian-relevant miR-219, the expression of which has been implicated in several cancers. A genome-wide expression microarray assay was carried out in a miR-219-overexpressed MCF-7 breast cancer cell line, which identified 319 differentially expressed transcripts. The identified transcriptional targets were analyzed for network and functional interrelatedness using the Ingenuity Pathway Analysis (IPA) software. Overexpression of miR-219 in MCF-7 breast cancer cells resulted in accentuated expression of apoptosis- and proliferation-related anti-viral immunodulators of the Jak-STAT and NF-κβ pathways. These findings suggest that long-term night shiftwork exposure may lead to the methylation-dependent downregulation of miR-219, which may in turn lead to the downregulation of immunomediated antitumor activity and increased breast cancer risk.

Identification of diverse full-length endogenous betaretroviruses in megabats and microbats

BACKGROUND

Betaretroviruses infect a wide range of species including primates, rodents, ruminants, and marsupials. They exist in both endogenous and exogenous forms and are implicated in animal diseases such as lung cancer in sheep, and in human disease, with members of the human endogenous retrovirus-K (HERV-K) group of endogenous betaretroviruses (βERVs) associated with human cancers and autoimmune diseases. To improve our understanding of betaretroviruses in an evolutionarily distinct host species, we characterized βERVs present in the genomes and transcriptomes of mega- and microbats, which are an important reservoir of emerging viruses.

RESULTS

A diverse range of full-length βERVs were discovered in mega- and microbat genomes and transcriptomes including the first identified intact endogenous retrovirus in a bat. Our analysis revealed that the genus Betaretrovirus can be divided into eight distinct sub-groups with evidence of cross-species transmission. Betaretroviruses are revealed to be a complex retrovirus group, within which one sub-group has evolved from complex to simple genomic organization through the acquisition of an env gene from the genus Gammaretrovirus. Molecular dating suggests that bats have contended with betaretroviral infections for over 30 million years.

CONCLUSIONS

Our study reveals that a diverse range of betaretroviruses have circulated in bats for most of their evolutionary history, and cluster with extant betaretroviruses of divergent mammalian lineages suggesting that their distribution may be largely unrestricted by host species barriers. The presence of βERVs with the ability to transcribe active viral elements in a major animal reservoir for viral pathogens has potential implications for public health.

Cell-to-cell miRNA transfer: from body homeostasis to therapy

The role of non-protein coding RNAs (ncRNAs), microRNAs (miRNAs) in particular, as fine-tuners of both pathological and physiological processes is no longer a matter of debate. With the recent discovery of miRNAs in a wide variety of body fluids and considering them as tools employed in horizontal gene transfer between cells, a new horizon opens in the field of diagnosis and therapeutics. Circulating miRNAs not only enable the communication among cells, but also provide insight into the pathological and physiological state of the originating cells. In this review we summarize the recent advances made in this field, arguing for compelling translation of miRNAs into clinical practice. Moreover, we provide overview of their characteristics and how they impact the evolution of tumor microenvironment and cell-to-cell communication, advancing the idea that miRNAs may function as hormones.

Epstein-Barr virus, human papillomavirus and mouse mammary tumour virus as multiple viruses in breast cancer

BACKGROUND

The purpose of this investigation is to determine if Epstein Barr virus (EBV), high risk human papillomavirus (HPV), and mouse mammary tumour viruses (MMTV) co-exist in some breast cancers.

MATERIALS AND METHODS

All the specimens were from women residing in Australia. For investigations based on standard PCR, we used fresh frozen DNA extracts from 50 unselected invasive breast cancers. For normal breast specimens, we used DNA extracts from epithelial cells from milk donated by 40 lactating women. For investigations based on in situ PCR we used 27 unselected archival formalin fixed breast cancer specimens and 18 unselected archival formalin fixed normal breast specimens from women who had breast reduction surgery. Thirteen of these fixed breast cancer specimens were ductal carcinoma in situ (dcis) and 14 were predominantly invasive ductal carcinomas (idc).

RESULTS

EBV sequences were identified in 68%, high risk HPV sequences in 50%, and MMTV sequences in 78% of DNA extracted from 50 invasive breast cancer specimens. These same viruses were identified in selected normal and breast cancer specimens by in situ PCR. Sequences from more than one viral type were identified in 72% of the same breast cancer specimens. Normal controls showed these viruses were also present in epithelial cells in human milk - EBV (35%), HPV, 20%) and MMTV (32%) of 40 milk samples from normal lactating women, with multiple viruses being identified in 13% of the same milk samples.

CONCLUSIONS

We conclude that (i) EBV, HPV and MMTV gene sequences are present and co-exist in many human breast cancers, (ii) the presence of these viruses in breast cancer is associated with young age of diagnosis and possibly an increased grade of breast cancer.

Lack of association of mouse mammary tumor virus-like sequences in Iranian breast cancer patients

OBJECTIVE

The present study aimed to detect mouse mammary tumor virus (MMTV)-like sequences in Iranian breast cancer patients in the city of Shiraz, located in southwest Iran.

SUBJECTS AND METHODS

We searched for two MMTV genetic regions in the peripheral blood leukocytes of 300 women with breast cancer, 300 age-matched healthy control subjects, and 50 breast tumor tissues. Two regions of MMTV, 660 bp and 250 bp, were searched by nested polymerase chain reactions.

RESULTS

None of the above two regions were detected. There were no differences between the control group and the breast cancer group.

CONCLUSION

Our findings did not show any association of MMTV-like sequences with breast cancer development in Iranian patients in Shiraz.

A mouse mammary tumor virus env-like exogenous sequence is strictly related to progression of human sporadic breast carcinoma

A viral etiology of human breast cancer (HBC) has been postulated for decades since the identification of mouse mammary tumor virus (MMTV). The detection of MMTV env-like exogenous sequences (MMTVels) in 30% to 40% of invasive HBCs increased attention to this hypothesis. Looking for MMTVels during cancer progression may contribute to a better understanding of their role in HBC. Herein, we analyzed HBC preinvasive lesions for the presence of MMTVels. Samples were obtained by laser microdissection of FFPE tissues: 20 usual-type ductal hyperplasias, 22 atypical ductal hyperplasias (ADHs), 49 ductal carcinomas in situ (DCISs), 20 infiltrating ductal carcinomas (IDCs), and 26 normal epithelial cells collateral to a DCIS or an IDC. Controls included reductive mammoplastic tissue, thyroid and colon carcinoma, and blood samples from healthy donors. MMTVels were detected by fluorescence-nested PCR. DNA samples from the tissues of nine patients were analyzed by real-time quantitative PCR, revealing a different viral load correlated with stage of progression. Furthermore, as never previously described, the presence of MMTVels was investigated by chromogenic in situ hybridization. MMTVels were found in 19% of normal epithelial cells collateral to a DCIS or an IDC, 27% of ADHs, 82% of DCISs, and 35% of IDCs. No MMTVels were found in the control samples. Quantitative PCR and chromogenic in situ hybridization confirmed these results. These data could contribute to our understanding of the role of MMTVels in HBC.

Genome-based and transcriptome-based molecular classification of breast cancer

PURPOSE OF REVIEW

The highly heterogeneous clinical, histological, biological and genetic nature of breast malignancies is due in part to their extreme molecular complexity.

RECENT FINDINGS

Many genetic and epigenetic alterations have been described, affecting a relatively small number of signaling pathways (PI3K, NK-κB, FGF, etc.) and thus several molecular subtypes of breast cancer have been identified.

SUMMARY

The next decade will see even more prolific developments, notably with the advent of next-generation sequencing (NGS) technologies capable of providing individual patients' constitutional and somatic genome sequences both rapidly and cheaply. Knowledge of the full catalogue of somatic genetic alterations will pave the way for fully individualized management of breast cancer patients.

Mouse mammary tumor like virus sequences in breast milk from healthy lactating women

Mouse mammary tumor virus (MMTV) has been a long standing candidate as a potential cause of some human breast cancers. Forty years ago, electron microscopic images of MMTV-like particles were identified in milk from 5% of healthy lactating women. These observations, however, have not been confirmed by modern methods. The purpose of this study was to confirm the presence of MMTV-like DNA sequences in human milk from normal lactating women. Standard and in situ PCR analyses were conducted on DNA extracted from fresh breast milk samples collected from a group of 91 healthy lactating women volunteers. The MMTV-like viral positive PCR products were sequenced and a phylogenetic tree was constructed to compare these sequences. Immunohistochemistry analyses were performed on breast milk cells using polyclonal rabbit antibodies against affinity-purified MMTV envelope glycoproteins 52/36. MMTV-like envelope gene sequences were identified by PCR in 5% (4/91) of breast milk samples from healthy lactating women volunteers. These observations were confirmed by in situ PCR and immunohistochemistry using MMTV gp52/36 antibodies. These findings confirm the presence of MMTV-like gene sequences in human milk. As MMTV is transmitted via milk from mouse mothers to their newborn pups to cause mammary tumors when they become adults, this indicates a means of transmission of this virus in humans.

Detection of human cytomegalovirus in normal and neoplastic breast epithelium

Introduction

Human cytomegalovirus (HCMV) establishes a persistent life-long infection, and can cause severe pathology in the fetus and the immunocompromised host[1]. Breast milk is the primary route of transmission in humans worldwide, and breast epithelium is thus a likely site of persistent infection and/or reactivation, though this phenomenon has not previously been demonstrated. Increasing evidence indicates HCMV infection can modulate signaling pathways associated with oncogenesis. We hypothesized that persistent HCMV infection occurs in normal adult breast epithelium and that persistent viral expression might be associated with normal and neoplastic ductal epithelium.

Methods

Surgical biopsy specimens of normal breast (n = 38) breast carcinoma (n = 39) and paired normal breast from breast cancer patients (n = 21) were obtained. Specimens were evaluated by immunohistochemistry, in situ hybridization, PCR and DNA sequencing for evidence of HCMV antigens and nucleic acids.

Results

We detected HCMV expression specifically in glandular epithelium in 17/27 (63%) of normal adult breast cases evaluated. In contrast, HCMV expression was evident in the neoplastic epithelium of 31/32 (97%) patients with ductal carcinoma in situ (DCIS) and infiltrating ductal carcinoma (IDC) cases evaluated (p = 0.0009).

Conclusions

These findings are the first to demonstrate that persistent HCMV infection occurs in breast epithelium in a significant percentage of normal adult females. HCMV expression was also evident in neoplastic breast epithelium in a high percentage of normal and neoplastic breast tissues obtained from breast cancer patients, raising the possibility that viral infection may be involved in the neoplastic process.

[Search for new genes involved in breast tumorigenesis by "Omics" analysis]

The high heterogeneity of clinical, histological, biological and genetic features in breast cancer is due in part to the extreme molecular complexity of these tumors. This review article presents the major technological advances of the past ten years, in particular the development of microarray approaches, which have enabled genome-wide ("Omics") analysis of these tumors. Numerous genetic and epigenetic alterations involving a small number of altered signalling pathways (PI3K, NK-κB, FGF, etc.) have been described. The next decade will be even more prolific in terms of discovery with the advent of next-generation sequencing (NGS) technologies that will provide fast and low cost constitutional and somatic genome sequences. The full catalogue of somatic genetic alterations will result in a completely new individual management for breast cancer patients.

Viruses and breast cancer

Viruses are the accepted cause of many important cancers including cancers of the cervix and anogenital area, the liver, some lymphomas, head and neck cancers and indirectly human immunodeficiency virus associated cancers. For over 50 years, there have been serious attempts to identify viruses which may have a role in breast cancer. Despite these efforts, the establishment of conclusive evidence for such a role has been elusive. However, the development of extremely sophisticated new experimental techniques has allowed the recent development of evidence that human papilloma virus, Epstein-Barr virus, mouse mammary tumor virus and bovine leukemia virus may each have a role in the causation of human breast cancers. This is potentially good news as effective vaccines are already available to prevent infections from carcinogenic strains of human papilloma virus, which causes cancer of the uterine cervix.