No association of mouse mammary tumor virus-related retrovirus with Japanese cases of breast cancer

Prevalence of MMTV-like sequences in breast cancer samples in Romanian patients-there is a geographic difference compared to the Western world

BACKGROUND

Breast cancer, although the most frequently diagnosed malignant tumor in humans, has a less clear etiology compared to other frequent cancer types. Mouse-mammary tumor virus (MMTV) is involved in breast cancer in mice and dogs and might play a role in the etiology of some breast cancers in humans, since an MMTV-like sequence was identified in 20-40% of breast cancer samples in Western Europe, USA, Australia and some other parts of the world. The purpose of our study was to identify MMTV-like DNA sequences in breast tissue samples from breast cancer patients who underwent curative surgery in our regional academic center in Romania, EU.

METHODS

We selected 75 patients with non-metastatic breast cancer treated surgically with curative intent, who did not undergo any neoadjuvant treatment. Out of these patients, 50 underwent radical lumpectomy and 25 modified radical mastectomy. Based on previous reports in the literature we searched using PCR the MMTV-like DNA env sequence in the breast cancer tissue and normal breast tissue obtained from the same patients.

RESULTS

None of the examined samples was positive for MMTV-like target sequences on PCR.

CONCLUSIONS

We could not prove that MMTV plays a role in the etiology of breast cancer in our patient group. This finding is similar to those from publications of other geographically related research groups.

The Viral Origin of Human Breast Cancer: From the Mouse Mammary Tumor Virus (MMTV) to the Human Betaretrovirus (HBRV)

A Human Betaretrovirus (HBRV) has been identified in humans, dating as far back as about 4500 years ago, with a high probability of it being acquired by our species around 10,000 years ago, following a species jump from mice to humans. HBRV is the human homolog of the MMTV (mouse mammary tumor virus), which is the etiological agent of murine mammary tumors. The hypothesis of a HMTV (human mammary tumor virus) was proposed about 50 years ago, and has acquired a solid scientific basis during the last 30 years, with the demonstration of a robust link with breast cancer and with PBC, primary biliary cholangitis. This article summarizes most of what is known about MMTV/HMTV/HBRV since the discovery of MMTV at the beginning of last century, to make evident both the quantity and the quality of the research supporting the existence of HBRV and its pathogenic role. Here, it is sufficient to mention that scientific evidence includes that viral sequences have been identified in breast-cancer samples in a worldwide distribution, that the complete proviral genome has been cloned from breast cancer and patients with PBC, and that saliva contains HBRV, as a possible route of inter-human infection. Controversies that have arisen concerning results obtained from human tissues, many of them outdated by new scientific evidence, are critically discussed and confuted.

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.

Presence of high-risk HPVs, EBV, and MMTV in human triple-negative breast cancer

Breast cancer, the most frequent disease amongst women worldwide, accounts for the highest cancer-related mortality rate. Triple-negative breast cancer (TNBC) subtype encompasses ~15% of all breast cancers and lack estrogen, progesterone, and HER2 receptors. Although risk factors for breast cancer are well-known, factors underpinning breast cancer onset and progression remain unknown. Recent studies suggest the plausible role of oncoviruses including human papillomaviruses (HPVs), Epstein-Barr virus (EBV), and mouse mammary tumor virus (MMTV) in breast cancer pathogenesis. However, the role of these oncoviruses in TNBC is still unclear. In the current study, we explored the status of high-risk HPVs, EBV, and MMTV in a well-defined TNBC cohort from Croatia in comparison to 16 normal/non TNBC samples (controls) using polymerase chain reaction assay. We found high-risk HPVs and EBV present in 37/70 (53%) and 25/70 (36%) of the cases, respectively. The most common HPV types are 52, 45, 31, 58 and 68. We found 16% of the samples positive for co-presence of high-risk HPVs and EBV. Moreover, our data revealed that 5/70 (7%) samples are positive for MMTV. In addition, only 2/70 (3%) samples had co-presence of HPVs, EBV, and MMTV without any significant association with the clinicopathological variables. While, 6/16 (37.5%) controls were positive for HPV (p = .4), EBV was absent in all controls (0/16, 0%) (p = .01). In addition, we did not find the co-presence of the oncoviruses in the controls (p > .05). Nevertheless, further investigations are essential to understand the underlying mechanisms of multiple-oncogenic viruses' interaction in breast carcinogenesis, especially TNBC.

Mouse Mammary Tumor Virus (MMTV)-Like env Sequence in Brazilian Breast Cancer Samples: Implications in Clinicopathological Parameters in Molecular Subtypes

Background: Breast cancer (BC) is a complex disease in which susceptibility and clinical course depend on multiple factors. Evidence suggests that a mouse mammary tumor virus (MMTV)-homolog may be present in human BCs; however, little is known about its clinical implications. Methods: MMTV-like env nucleotide-sequence was searched in tumor and tumor-adjacent tissues from 217 Brazilian BC patients through nested-PCR and confirmed through PCR-sequencing. Blood samples were also tested for patients with MMTV-like env gene-positive tumors. Correlations with clinicopathological parameters were evaluated. Results: MMTV-like env sequence was detected in tumor and tumor-adjacent tissue samples from 41/217 and 30/196 patients, respectively. In blood, MMTV-like was detected in 17/32 patients. In Luminal-B tumors, MMTV-like in tumor tissue was negatively correlated with tumor size and disease stage, whereas in HER2 tumors it anti-correlated with lymph node metastasis (LNM) and disease stage. Considering blood, MMTV-like env gene positivity negatively correlated with age in general BC, while in Luminal-A tumors it positively correlated with Ki67 but negatively correlated with age and LNM. The associations with decreased LNM frequency were independent of other prognostic factors. Conclusion: MMTV-like env positivity is associated with better prognostic parameters in BC subtypes, which might be explainable by its anti-metastatic potential and by putative activation of immune milieu.

Seroprevalence of Human Betaretrovirus Surface Protein Antibodies in Patients with Breast Cancer and Liver Disease

Mouse mammary tumor virus (MMTV) is a betaretrovirus that plays a causal role in the development of breast cancer and lymphoma in mice. Closely related sequences that share 91-99% nucleotide identity with MMTV have been repeatedly found in humans with neoplastic and inflammatory diseases. Evidence for infection with a betaretrovirus has been found in patients with breast cancer and primary biliary cholangitis and referred to as the human mammary tumor virus and the human betaretrovirus (HBRV), respectively. Using the gold standard technique of demonstrating retroviral infection, HBRV proviral integrations have been detected in cholangiocytes, lymph nodes, and liver of patients with primary biliary cholangitis. However, the scientific biomedical community has not embraced the hypothesis that MMTV like betaretroviruses may infect humans because reports of viral detection have been inconsistent and robust diagnostic assays are lacking. Specifically, prior serological assays using MMTV proteins have produced divergent results in human disease. Accordingly, a partial HBRV surface (Su) construct was transfected into HEK293 to create an ELISA. The secreted HBRV gp52 Su protein was then used to screen for serological responses in patients with breast cancer and liver disease. A greater proportion of breast cancer patients (n = 98) were found to have serological reactivity to HBRV Su as compared to age- and sex-matched control subjects (10.2% versus 2.0%, P=0.017, OR = 5.6 [1.25-26.3]). Similarly, the frequency of HBRV Su reactivity was higher in patients with primary biliary cholangitis (n  =  156) as compared to blood donors (11.5% vs. 3.1%, P=0.0024, OR = 4.09 [1.66-10.1]). While the sensitivity of the HBRV Su ELISA was limited, the assay was highly specific for serologic detection in patients with breast cancer or primary biliary cholangitis, respectively (98.0% [93.1%-99.7%] and 97.0% [93.4%-98.6%]). Additional assays will be required to link immune response to betaretrovirus infection and either breast cancer or primary biliary cholangitis.

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.

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.

High prevalence of mouse mammary tumor virus-like gene sequences in breast cancer samples of Iranian women

Mouse mammary tumor virus (MMTV) is considered to be responsible for breast tumor development in mice. In several instances sequences homologous to the genome of this virus have been reported in human breast cancer samples. Here we aimed to evaluate MMTV involvement in human breast cancer development. DNA was extracted from 118 formalin fixed and paraffin embedded malignant (n = 59) and benign (n = 59) breast lesions. Using two sets of outer and inner MMTV-like envelope specific primers, in a nested PCR setup, MMTV genome was detected in 19 samples out of 59 (%32.2) cases of breast carcinomas, while in non-malignant breast tissue samples, only 3 samples out of 59 (%5) were positive. The difference was statistically highly significant (p < 0.001). Alignment of PCR amplified sequences with BR6, GR and C3H mouse mammary tumor virus strains emerged to be around 99% identical which is indicative of tumor tissue infection by an exogenous mouse MMTV genome.

Low prevalence of human mammary tumor virus (HMTV) in breast cancer patients from Myanmar

BACKGROUND

Human mammary tumor virus (HMTV) is 90-95% homologous to mouse mammary tumor virus (MMTV), one of the causal agents of murine mammary tumors. HMTV (MMTV-like) sequences were reported to be present in human breast cancers from several populations with a prevalence range of 0-78%; however, the prevalence of HMTV in breast cancers from Myanmar remains unknown.

METHODS

Fifty-eight breast cancer samples from Myanmar women were examined in this study. DNA was isolated from formalin-fixed paraffin-embedded specimens, and HMTV envelope sequences were detected by semi-nested PCR. The sequence of the PCR products was also confirmed.

RESULTS

Only 1.7% (1 of 58) of the breast cancers were positive for HMTV, and the sequence of PCR products was 98.9% identical to the reference HMTV sequence (GenBank accession No. AF243039). The tumor with HMTV was grade III invasive ductal carcinoma, 7.0 cm in size with lymph node metastasis (T3, N1, M0).

CONCLUSIONS

We, for the first time, investigated the presence of HMTV in Myanmar breast cancer patients. In accordance with other Asian studies, the prevalence of HMTV in Myanmar was quite low, supporting the hypothesis that Asian breast cancers have different etiologies than in Western countries, where HMTV is more prevalent.

Evaluation Frequency of Merkel Cell Polyoma, Epstein-Barr and Mouse Mammary Tumor Viruses in Patients with Breast Cancer in Kerman, Southeast of Iran

Breast cancer is the most common cancer among women worldwide. Roles of the Epstein-Barr, Merkel cell polyoma and mouse mammary tumor viruses in breast carcinogenesis are still controversial although any relationship would clearly be important for breast cancer etiology, early detection and prevention. In the present study associations between EBV, MMTV and Merkel cell polyoma virus and breast cancer in 100 Iranian patients were evaluated using paraffin-embedded tissues. EBER RNA and expression of p53 and large T antigen were evaluated by real time PCR and CD34, p63, HER2, PR and ER markers were studied by immunohistochemistry. EBV was detected in 8/100 (8%), MMTV in 12/100 (12%), MPy in 3/100 (3%) and EBER RNA in 18/100 (18%) cases. None of the control samples demonstrated any of the viruses. p53 was suppressed in EBV, MPy and MMTV positive samples. The large T antigen rate was raised in MPy positive samples. Our results showed that EBV, MMTV and the Merkel cell polyoma virus are foundwith some proportion of breast cancers in our patients, suggesting that these viruses might have a significant role in breast cancer in Kerman, southeast of Iran.

Prevalence of HMTV in breast carcinomas and unaffected tissue from Mexican women

Background

Breast cancer is a complex multifactorial genetic disease. Among other factors, race and, to an even greater extent, viruses are known to influence the development of this heterogeneous disease. It has been reported that MMTV-like (HMTV) gene sequences with a 90 to 98% homology to mouse mammary tumor virus are found in several populations with a prevalence range of 0 to 74%. In the Mexican population, 4.2% of patients with breast cancer exhibit the presence of HMTV (MMTV-like) sequences. The aim of this study was to evaluate the presence and current prevalence of retroviral HMTV (MMTV-like) sequences in breast cancer in Mexican women.

Methods

We used nested PCR and real-time PCR with a TaqMan probe. As a positive control, we used the C3H MMTV strain inserted into pBR322 plasmid. To confirm that we had identified the HMTV sequences, we sequenced the amplicons and compared these sequences with those of MMTV and HMTV (GenBank AF033807 and AF346816).

Results

A total of 12.4% of breast tumors were HMTV-positive, and 15.7% of the unaffected tissue samples from 458 patients were HMTV-positive. A total of 8.3% of the patients had both HMTV-positive tumor and adjacent tissues. The HMTV-positive samples presented 98% similarity to the reported HMTV sequence.

Conclusions

These results confirm that the HMTV sequence is present in breast tumors and non-affected tissues in the Mexican population. HMTV should be considered a prominent causative agent of breast 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.

No association between Epstein-Barr Virus and Mouse Mammary Tumor Virus with breast cancer in Mexican women

Breast cancer is the most frequent malignancy affecting women worldwide. It has been suggested that infection by Epstein Barr Virus (EBV), Mouse Mammary Tumor Virus or a similar virus, MMTV-like virus (MMTV-LV), play a role in the etiology of the disease. However, studies looking at the presence of these viruses in breast cancer have produced conflicting results, and this possible association remains controversial. Here, we used polymerase chain reaction assay to screen specific sequences of EBV and MMTV-LV in 86 tumor and 65 adjacent tissues from Mexican women with breast cancer. Neither tumor samples nor adjacent tissue were positive for either virus in a first round PCR and only 4 tumor samples were EBV positive by a more sensitive nested PCR. Considering the study's statistical power, these results do not support the involvement of EBV and MMTV-LV in the etiology of breast cancer.

Genomic DNA of MCF-7 breast cancer cells not an ideal choice as positive control for PCR amplification based detection of Mouse Mammary Tumor Virus-Like Sequences

The identification of the etiology of breast cancer is a crucial research issue for the development of an effective preventive and treatment strategies. Researchers are exploring the possible involvement of Mouse Mammary Tumor Virus (MMTV) in causing human breast cancer. Hence, it becomes very important to use a consistent positive control agent in PCR amplification based detection of MMTV-Like Sequence (MMTV-LS) in human breast cancer for accurate and reproducible results. This study was done to investigate the feasibility of using genomic DNA of MCF-7 breast cancer cells to detect MMTV-LS using PCR amplification based detection. MMTV env and SAG gene located at the 3' long terminal repeat (LTR) sequences were targeted for the PCR based detection. No amplification was observed in case of the genomic DNA of MCF-7 breast cancer cells. However, the 2.7 kb DNA fragment comprising MMTV env and SAG LTR sequences yielded the products of desired size. From these results it can be concluded that Genomic DNA of MCF-7 cell is not a suitable choice as positive control for PCR or RT-PCR based detection of MMTV-LS. It is also suggested that plasmids containing the cloned genes or sequences of MMTV be used as positive control for detection of MMTV-LS.

Are viruses associated with human breast cancer? Scrutinizing the molecular evidence

The three viruses most studied as possible causes of human breast cancer are mouse mammary tumor virus-like sequences (MMTV-LS), Epstein-Barr virus (EBV), and oncogenic (high risk) types of human papilloma virus (HPV). The first step in fulfilling traditional criteria for inferring that a cancer is caused by a virus is to demonstrate the virus in the affected tissue. Molecular techniques, compared to host antibody assessment and immunohistochemistry, are the most definitive in establishing viral presence. Results of 85 original molecular research investigations to detect one or more of the three viruses have been extremely divergent with no consensus reached. We evaluated the methodology of these studies for the following: type of molecular assay, DNA/RNA quality control, positive and negative assay controls, type of fixation, genome targets, methods for preventing and detecting molecular contamination, pathology of specimens processed, sample size, and proportion of specimens positive for the viral genome region targeted. Only seven of the studies convincingly demonstrated the presence of an oncogenic virus biomarker (EBV: 4/30 studies (13%); HPV 3/29 studies (10%), whereas 25 convincingly demonstrated absence of the virus studied (MMTV-LS: 4/25 (16%); EBV: 15/30 (50%); 6/29 (21%). The remainder of the studies suffered shortcomings, which, in our opinion, prevented a definitive conclusion. Only one of the studies compared frequency of the virus in breast tissue of breast cancer patients versus appropriate normal control subjects with no history of breast cancer. None of the studies were designed as epidemiologic studies to determine if the presence of the virus was significantly associated with breast cancer. Based on our evaluation, the data in the publications reviewed here remain preliminary, and do not justify a conclusion that MMTV-LS, HPV, or EBV are causally associated with breast cancer. However, they form a valuable basis for redirecting future studies.

Mouse mammary tumor virus-like nucleotide sequences in canine and feline mammary tumors

Mouse mammary tumor virus (MMTV) has been speculated to be involved in human breast cancer. Companion animals, dogs, and cats with intimate human contacts may contribute to the transmission of MMTV between mouse and human. The aim of this study was to detect MMTV-like nucleotide sequences in canine and feline mammary tumors by nested PCR. Results showed that the presence of MMTV-like env and LTR sequences in canine malignant mammary tumors was 3.49% (3/86) and 18.60% (16/86), respectively. For feline malignant mammary tumors, the presence of both env and LTR sequences was found to be 22.22% (2/9). Nevertheless, the MMTV-like LTR and env sequences also were detected in normal mammary glands of dogs and cats. In comparisons of the MMTV-like DNA sequences of our findings to those of NIH 3T3 (MMTV-positive murine cell line) and human breast cancer cells, the sequence similarities ranged from 94 to 98%. Phylogenetic analysis revealed that intermixing among sequences identified from tissues of different hosts, i.e., mouse, dog, cat, and human, indicated the MMTV-like DNA existing in these hosts. Moreover, the env transcript was detected in 1 of the 19 MMTV-positive samples by reverse transcription-PCR. Taken together, our study provides evidence for the existence and expression of MMTV-like sequences in neoplastic and normal mammary glands of dogs and cats.

DNA of mouse mammary tumor virus-like virus is present in human tumors influenced by hormones

Mouse mammary tumor virus (MMTV) is a hormonally regulated, oncogenic virus of mice. MMTV-like virus DNA has previously been detected in human breast cancers, liver disease, and liver cancers. It is hypothesized that local hormonal effects might be of primary importance in determining MMTV-like virus detection in human tumors. MMTV-like virus envelope (env) DNA was determined using nested PCR in 89 ovarian, 147 prostate, 50 endometrial, 141 skin, and 51 lung cancers. Viral-positive sequences were compared with published MMTV-like viral sequences from human breast cancer, liver cancer and MMTV. Immunohistochemistry for estrogen receptor (ER-alpha) and progesterone receptor (PgR) was performed on a subset of tumors. MMTV-like virus env DNA was detected in ovarian cancers (14/89; 16%), prostate cancers (53/147; 36%), endometrial cancers (5/50; 10%), skin cancers (13/141; 9%) but not in lung cancers (0/51). Phylogenetic analysis of the viral-positive sequences showed no clustering of the isolates according to tissue type. A significant association was observed between the presence of hormone receptors and detection of MMTV-like virus in the human cancers screened (P = 0.01). A significant association between MMTV-like virus and PgR was noted in skin cancers (P = 0.003). Therefore, unlike the mouse model, the detection of MMTV-like env sequences in human cancers in addition to breast indicates that MMTV-like viral expression is not breast cancer-specific and may relate to hormone-dependent viral expression.

Human mammary tumor virus in inflammatory breast cancer

The authors have found that retroviral sequences with 85% to 95% homology to the mouse mammary tumor virus were present in 40% of the sporadic breast cancers of American women. These sequences were not found in normal breasts or other tumors. A whole proviral structure was detected in 2 tumors. Breast cancer cells in culture were shown to contain and shed betaretroviral particles. This virus was designated human mammary tumor virus (HMTV). The authors have investigated the presence of HMTV sequences in a variety of breast conditions and geographic locations. Here they report that inflammatory breast cancer from American women shows a higher incidence of viral sequences (71%) than sporadic breast cancers. Similar incidence has been found in inflammatory breast cancers from Tunisia, and in gestational breast cancers. Because these conditions represent highly invasive malignancies, it is concluded that HMTV is sometimes associated with a particularly malignant phenotype.

No evidence of MMTV-like env sequences in specimens from the Australian Breast Cancer Family Study

Numerous independent groups from a range of countries have reported a high prevalence of Mouse Mammary Tumour Virus (MMTV)-like env sequences in human breast cancer specimens, including a prevalence of almost 40% in Australia. MMTV-like sag sequences and a completely integrated provirus have also been described. Recently, it was reported that MMTV is capable of productive infection of human breast cells in vitro. Conclusive demonstration of an association between MMTV and human breast cancer has remained elusive, and negative findings from a number of independent studies have questioned the role of MMTV as an aetiological agent. We used breast cancer specimens from women in the Australian Breast Cancer Family Study (ABCFS) who were diagnosed with first primary invasive breast cancer before the age of 40 years. Specimens were selected for higher grade cancers and for diagnosis relatively soon after childbirth. We searched for MMTV-like env sequences in tumour-enriched DNA using a nested PCR designed to detect all MMTV variants represented in GenBank, including those reportedly detected in human breast cancers. Forty-two specimens were deemed adequate for testing based on strong β-globin PCR. Despite the MMTV nested PCR regimen consistently detecting five copies of control plasmid against a background of MMTV-negative human genomic DNA, no MMTV env sequence was detected in any of the breast cancer specimens. Our findings appear inconsistent with previous reports on Australian breast cancer specimens but consistent with a growing number of independent negative reports internationally. We recommend caution in inferring a role for MMTV or a closely related virus in human breast cancer and suggest that universally regarded alternative lines of evidence such as highly specific serology data will be required to support such an association.

The possible involvement of virus in breast cancer

It is well known that the etiology of human breast cancer is significantly affected by environmental factors. Virus-associated cancer refers to a cancer where viral infection results in the malignant transformation of the host's infected cells. Human papillomaviruses (HPV), mouse mammary tumor virus (MMTV) and Epstein-Barr (EBV) virus are prime candidate viruses as agents of human breast cancer. The precise role that viruses play in tumorigenesis is not clear, but it seems that they are responsible for causing only one in a series of steps required for cancer development. The idea that a virus could cause breast cancer has been investigated for quite some time, even though breast cancer could be a hereditary disease; however, hereditary breast cancer is estimated to account for a small percentage of all breast cancer cases. Based on current research, this review present at moment, substantial, but not conclusive, evidence that HPV, EBV and MMTV may be involved in breast cancer.