MMTV-like Env Research Articles

Decoding the mystery of MMTV-like virus and its relationship with breast cancer metastasis

BackgroundMMTV causes mammary tumors in mice, and it is associated with invasive and aggressive forms of breast cancer in humans. However, the underlying mechanisms are yet unknown. We aimed to determine the MMTV-like virus (MMTV-LV) association with histological types of breast cancer, nodal involvement, and metastasis. MethodsFirst, 105 breast cancer biopsies and 15 disease-free biopsies were collected. Details of clinicopathological characteristics were retrieved from patients’ records. The status of MMTV-LV was already known for these biopsy samples. Associations of MMTV-LV prevalence with LNM status and metastatic history were determined. Next, quantitative PCR (qPCR) was used to quantify env gene mRNA in biopsies positive for MMTV-LV. Expression of the env gene was compared against different histopathological types of mammary tumor, LNM status, and metastasis by performing Ordinary One Way ANOVA followed by Tukey’s multiple comparisons test. ResultsMMTV-LV prevalence was found to have no significant association with LNM or metastatic history. As compared to normal control, expression of the env gene was significantly higher (>2.8 folds) in invasive samples (P-value: < 0.01). Expression was also higher (3.28 and 2.89 folds) in patient samples with LNM (P-value: 0.0006) or metastatic history (P-value: < 0.0001), respectively. ConclusionWe conclude that MMTV-LV prevalence is not associated with LNM status or breast cancer metastasis; samples with invasive phenotypes, nodal involvement, and metastasis exhibit significantly higher expression of the MMTV-like env gene.

Interferon-gamma plasma levels and presence of mouse mammary tumor virus-like env gene: Implications on the pathogenesis of breast cancer

Mouse mammary tumor virus (MMTV) is a retrovirus that has been associated with the development of breast cancer (BC) in mice. The identification of a 95% homologous gene sequence to MMTV in human BC samples has increased interest in this hypothesis. This virus in humans received the name of mouse mammary tumor virus-like (MMTV-like). Several cytokines may be involved in the interactions between MMTV and the immune system, such as interferon-gamma (IFN-γ), which can enhance Th1-mediated antitumor immune response but it can also play a protumorigenic role by transmitting antiapoptotic and proliferative signals. Little is known about the antiviral immune response in a microenvironment with the presence of MMTV-like in BC patients. Therefore, the purpose of the present study was to quantify the plasma levels of IFN-γ in the peripheral blood of 123 neoplasia-free donors and 98 BC patients of different molecular subtypes, by enzyme-linked immunosorbent assay (ELISA), and evaluate the association of these plasma levels with the detection of the MMTV-like env gene in tumor tissue. Correlation analyzes involving IFN-γ plasma levels and clinical-pathological parameters were performed by Kendall Tau-c test. In our study, a decrease in IFN-γ levels was observed in the group of BC patients (30.85 ± 57.49 pg/ml) compared to the control group (115.00 ± 176.80 pg/ml) (p < 0.0001). In the analysis by stratified BC molecular subtypes, Luminal-A (30.79 ± 61.04 pg/ml; p < 0.0001), Luminal-B (24.74 ± 25.78 pg/ml; p = 0.0188) and triple-negative (23.95 ± 40.45 pg/ml; p = 0.0005) had a lower plasma level compared to control group. There was no significant difference between IFN-γ plasma levels of MMTV-like DNA positive samples compared to MMTV-negative samples (p = 0.2056). In general BC, patients with larger tumor size had higher IFN-γ plasma levels (Tau-c = 0.202; p = 0.019). By analyzing the MMTV-like env negative samples, we could identify that IFN-γ plasma levels were higher in larger tumor size (Tau-c = 0.222; p = 0.020) and with greater lymph node involvement (Tau-c = 0.258; p = 0.042). Also, higher IFN-γ plasma levels were observed in patients with higher histopathological grades (Tau-c = 0.384; p = 0.019) in MMTV-like env positive samples. For the first time, we assessed the association between plasma levels of IFN-γ and the presence of the MMTV-like env gene in BC samples. However, more studies are needed to clarify whether the high levels of IFN-γ in MMTV-like env positive samples are reflecting a possible antiviral immune response or whether this cytokine is promoting tumor growth.

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

BackgroundBreast 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.MethodsWe 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.ResultsNone of the examined samples was positive for MMTV-like target sequences on PCR.ConclusionsWe 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.

Involvement of APOBEC3A/B Deletion in Mouse Mammary Tumor Virus (MMTV)-like Positive Human Breast Cancer.

The association between mouse mammary tumor virus (MMTV)-like sequences and human breast cancer (BC) is largely documented in the literature, but further research is needed to determine how they influence carcinogenesis. APOBEC3 cytidine deaminases are viral restriction factors that have been implicated in cancer mutagenesis, and a germline deletion that results in the fusion of the APOBEC3A coding region with the APOBEC3B 3'-UTR has been linked to increased mutagenic potential, enhanced risk of BC development, and poor prognosis. However, little is known about factors influencing APOBEC3 family activation in cancer. Thus, we hypothesized that MMTV infection and APOBEC3-mediated mutagenesis may be linked in the pathogenesis of BC. We investigated APOBEC3A/B genotyping, MMTV-like positivity, and clinicopathological parameters of 209 BC patients. We show evidence for active APOBEC3-mediated mutagenesis in human-derived MMTV sequences and comparatively investigate the impact of APOBEC3A/B germline deletion in MMTV-like env positive and negative BC in a Brazilian cohort. In MMTV-like negative samples, APOBEC3A/B deletion was negatively correlated with tumor stage while being positively correlated with estrogen receptor expression. Although APOBEC3A/B was not associated with MMTV-like positivity, samples carrying both MMTV-like positivity and APOBEC3A/B deletion had the lowest age-at-diagnosis of all study groups, with all patients being less than 50 years old. These results indicate that APOBEC3 mutagenesis is active against MMTV-like sequences, and that APOBEC3A/B deletion might act along with the MMTV-like presence to predispose people to early-onset BC.

MMTV-like Env sequences from human breast cancer patients cannot yet be considered as a separate species

Background: Mouse mammary tumour virus (MMTV), a betaretrovirus, causes breast cancer in mice. Since its discovery, scores of studies have reported the detection of MMTV-like antigens and sequences primarily in human breast cancer, but not normal tissues. The presence of these sequences in humans has been hypothesised to be possibly due to zoonosis of MMTV into humans, named human mammary tumour virus (HMTV). However, many groups have not been able to repeat these findings, making these observations controversial. Over the years, an increasing number of HMTV env gene sequences from human breast cancer patients worldwide have been deposited in GenBank and other repositories. Aims and Objectives: The aim of this study was to use the current bioinformatic tools to analyse these highly homologous sequences to determine if any signature sequences could be associated specifically with HMTV. Materials and Methods: We first built an MMTV env gene consensus sequence (MMTV_CON) from the 41 MMTV sequences available in the database that was used to align the reported HMTV sequences (n = 333). Results: As expected, the MMTV envs showed 4-5% genetic variation within the mouse isolates. Alignment of MMTV_CON with those from HMTV revealed ten nucleotide variations that were like those observed within MMTV env, showing that the two viral strains could not be distinguished. Conclusion: Thus, we conclude that despite extensive data, inadequate env coverage, conservation of MMTV and HMTV envs and limitations in HMTV study design suggest that HMTV cannot be considered a separate species until the availability of more data covering full-length env or HMTV genome.

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

BackgroundDespite 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.MethodsIn 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.ResultsWe 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).ConclusionThe 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.

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

BackgroundMouse 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 MethodsThe 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.ResultsMMTV 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.ConclusionMMTV 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.

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.

Mouse mammary tumour virus-like env nucleotide and p14 signal peptide are present in feline mammary carcinomas, but not in neoplastic or dysplastic canine mammary lesions.

Mouse mammary tumour virus-like (MMTV-like) is suspected to be involved in human breast cancer and it has been hypothesized that companion animals might have a role in viral transmission. The aim of our study was to investigate the presence of MMTV-like nucleotide sequences and viral protein in a larger number of feline (FMCs) and canine mammary carcinomas (CMCs) by nested PCR and immunohistochemistry. Results showed that the presence of MMTV-like env sequence in FMCs was 7% (6/86), while all the CMCs and canine dysplastic lesions scored negative. All PCR-positive FMCs scored positive for the MMTV p14 signal peptide of the envelope precursor protein of the virus. In contrast, all PCR-negative FMCs and canine mammary lesions were also negative for immunohistochemistry analysis. Canine and feline normal mammary gland tissues scored negative for both PCR and MMTV-p14 protein. Multiple nucleotide alignment of MMTV-like env gene sequences isolated from cat showed 97% and 99% similarity with HMTV and MMTV, respectively, while the others two presented some polimorphisms. Particularly the sequences of one of these two tumors showed a polymorphism (c.7575 A> G), that causes a previously unreported amino acid substitution (Thr > Ala). In conclusion, the results of our study showed the presence of MMTV-like sequences and viral protein in some FMCs. Further studies are needed to understand whether this virus does play a role in the development of FMCs, if MMTV-like is an exogenous virus as these data suggest and, in such a case, how and from whom this virus was acquired.

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

BackgroundBreast 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.MethodsDetection 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.ResultsThe 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.ConclusionWe 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.

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

BackgroundThere 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.MethodsPolymerase 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.ResultsMMTV-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.ConclusionsThe 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.

Detection of MMTV-Like sequences in Moroccan breast cancer cases

IntroductionThe 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.MethodsIn 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.ResultsSpecific 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).ConclusionsThis 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.

Detection and identification of mouse mammary tumor virus-like DNA sequences in blood and breast tissues of breast cancer patients.

Mouse mammary tumor virus (MMTV) is a well-known cause of mammary tumors in mice transmitted as endogenous proviruses or exogenously as infectious virions. The hypothesis that a retrovirus homologous to MMTV is involved in human breast cancers has resulted in renewed interest in the etiology of human breast cancer. Therefore, the detection of MMTV-like exogenous sequences in 30-40 % of invasive breast cancer has increased attention towards this hypothesis. To detect the prevalence of MMTV in Pakistani population, 666-bp-long MMTV envelop and 630-bp LTR sequences were amplified from breast cancer patient samples (tissue biopsies and peripheral blood) using mouse with mammary tumor as control. MMTV-like virus env and LTR DNA sequences were detected in 20 and 26 % of breast tumor samples, respectively, from the total of 80 breast cancer patients' blood and tissue samples. No significant association was observed between age, grade of disease, and lymph node involvement with the prevalence of MMTV-like sequences. Our data add to the growing number of studies implicating MMTV-like virus in human breast cancer, but still clear causal association of MMTV to breast cancer remains to be reputable.

Lack of Detection of the Mouse Mammary Tumor-like Virus (MMTV) Env Gene in Iranian Women Breast Cancer using Real Time PCR

Mouse mammary tumor virus (MMTV) is the major cause of mammary tumors in mice. There is limited controversial evidence about the probable etiologic role of MMTV- like virus in human breast cancer. A total of 40 Formalin fixed paraffin embedded samples with diagnosis of breast cancer were collected in a period of 3 years from cancer institute of Iran. We selected both pre-menopausal and post-menopausal patients with different histologic grades and different ethnic groups. We evaluated presence of MMTV-like virus env gene through real time PCR method. Forty patients (20 pre and 20 post- menopausal women) were evaluated with the mean age of 49.67. The average tumor size was 39 mm. None of the studied samples were positive for MMTV-like virus env gene target sequences. We found no evidence on the potential role of MMTV-like virus in the carcinogenicity of breast cancer among Iranian women.

Expression of MMTV-Like Env Gene in Egyptian Breast Cancer Patients

Expression of MMTV-Like Env Gene in Egyptian Breast Cancer Patients

Mouse mammary tumor virus-like gene sequences are present in lung patient specimens

BackgroundPrevious studies have reported on the presence of Murine Mammary Tumor Virus (MMTV)-like gene sequences in human cancer tissue specimens. Here, we search for MMTV-like gene sequences in lung diseases including carcinomas specimens from a Mexican population. This study was based on our previous study reporting that the INER51 lung cancer cell line, from a pleural effusion of a Mexican patient, contains MMTV-like env gene sequences.ResultsThe MMTV-like env gene sequences have been detected in three out of 18 specimens studied, by PCR using a specific set of MMTV-like primers. The three identified MMTV-like gene sequences, which were assigned as INER6, HZ101, and HZ14, were 99%, 98%, and 97% homologous, respectively, as compared to GenBank sequence accession number AY161347. The INER6 and HZ-101 samples were isolated from lung cancer specimens, and the HZ-14 was isolated from an acute inflammatory lung infiltrate sample. Two of the env sequences exhibited disruption of the reading frame due to mutations.ConclusionIn summary, we identified the presence of MMTV-like gene sequences in 2 out of 11 (18%) of the lung carcinomas and 1 out of 7 (14%) of acute inflamatory lung infiltrate specimens studied of a Mexican Population.

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.

Presence of MMTV-like env gene sequences in human breast cancer

Presence of MMTV-like env gene sequences in human breast cancer

Mouse mammary tumor-like virus and human breast cancer

Park et al. from Melbourne, Australia, report their failure toidentify by standard polymerase chain reaction (PCR)techniques, mouse mammary tumor virus (MMTV)-likeenv sequences in DNA extracted from 42 formalin-fixedinvasive breast cancer specimens, all from women living inMelbourne [1]. This negative outcome is in stark contrastto the many reports of the positive identification ofMMTV-like env sequences in breast cancers from inde-pendent laboratories in Australia, Argentina, China, Italy,Mexico, Tunisia, and the United States [2]. However, inpast years other workers have also failed to identify thesesequences in breast cancers [3–5].One reason for these differing outcomes is likely to bethe use of different primers for PCR analyses. Park et al.used primers that differ entirely from those identified ini-tially by the Pogo group from New York [6]. These latterprimers have been used in virtually all the more recentpositive identifications of MMTV-like env sequences inbreast tumors. Further, the identification and nuclearlocation of these sequences have been confirmed by in situPCR techniques which largely overcome the problem ofcontamination often associated with standard PCR [2, 7].In addition there is a concern about the ability of theprimers used by Park et al. to detect MMTV envelopesequences, since they used ‘‘fresh dilutions of p203[MMTV carrying plasmid] to yield five plasmid copiesagainst 10 ng MMTV – negative human genomic DNA’’ asa control. Clearly this plasmid has 100% complementarysequences to the primers chosen. Even though, they showin Fig. 1 the primers they used have perfect homology to anumber of MMTV’s from mice, they do not show thatthese primers are able to amplify sequences from mousegenomic DNA carrying these MMTV’s (ideally mixed withMMTV negative human genomic DNA) or more impor-tantly, carrying different (wild) isolates of MMTV that mayhave different sequences in these primer complementaryregions.The interesting question that arises from these variationsin findings is ‘‘why is it so?’’, why do primers identified byPogo give positive outcomes, but other primers also basedon MMTV envelope gene sequences give negative out-comes? The brief answer is, ‘‘we do not know’’.In our view, the evidence for a possible role of MMTV-like virus in human breast cancer is substantial. We haveoutlined this evidence in recent publications [2, 8].

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.