The role of infectious agents in urogenital cancers

Chlamydia muridarum Associated Pulmonary and Urogenital Disease and Pathology in a Colony of Enzootically Infected Il12rb2 Deficient and Stat1 Knockout Mice

Chlamydia muridarum (Cm), an intracellular bacterium of historical importance, was recently rediscovered as moderately prevalent in research mouse colonies. Cm was first reported as a causative agent of severe pneumonia in mice about 80 y ago, and while it has been used experimentally to model Chlamydia trachomatis infection of humans, there have been no further reports of clinical disease associated with natural infection. We observed clinical disease and pathology in 2 genetically engi- neered mouse (GEM) strains, Il12rb2 KO and STAT1 KO, with impaired interferon-γ signaling and Th1 CD4+ T cell responses in a colony of various GEM strains known to be colonized with and shedding Cm. Clinical signs included poor condition, hunched posture, and poor fecundity. Histopathology revealed disseminated Cm with lesions in pulmonary, gastrointestinal, and urogenital tissues. The presence of Cm was confirmed using both immunohistochemistry for Cm major outer membrane protein-1 antigen and in situ hybridization using a target probe directed against select regions of Cm strain Nigg. Cm was also found in association with a urothelial papilloma in one mouse. These cases provide additional support for excluding Cm from research mouse colonies.

The Role of the Human Microbiome in Epithelial Ovarian Cancer

Ovarian cancer is the fifth-leading cause of cancer deaths among women due to the absence of available screening methods to identify early disease. Thus, prevention and early disease detection investigations are of high priority, surrounding a critical window of opportunity to better understand important pathogenic mechanisms of disease progression. Microorganisms modulate molecular interactions in humans that can influence states of health and disease, including ovarian cancer. While the mechanisms of infectious microbial invasion that trigger the immune-inflammatory axis are well studied in cancer research, the complex interactions that promote the transition of noninfectious healthy microbes to pathobiont expansion are less understood. As traditional research has focused on the influences of infectious pathogens on ovarian cancer development and progression, the impact of noninfectious microbes has gained scientific attention. The objective of this chapter is to summarize current evidence on the role of microbiota in epithelial ovarian cancer throughout disease.

Chlamydial and Gonococcal Genital Infections: A Narrative Review

Sexually transmitted infections (STIs) constitute one of the leading causes of disease burden worldwide, leading to considerable morbidity, mortality, health expenditures, and stigma. Of note are the most common bacterial STIs, chlamydial and gonococcal infections, whose etiological agents are Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (NG), respectively. Despite being usually asymptomatic, in some cases these infections can be associated with long-term severe complications, such as pelvic inflammatory disease, chronic pelvic pain, infertility, ectopic pregnancy, and increased risk of other STIs acquisition. As the symptoms, when present, are usually similar in both infections, and in most of the cases these infections co-occur, the dual-test strategy, searching for both pathogens, should be preferred. In line with this, herein we focus on the main aspects of CT and NG infections, the clinical symptoms as well as the appropriate state-of-the-art diagnostic tests and treatment. Cost-effective strategies for controlling CT and NG infections worldwide are addressed. The treatment for both infections is based on antibiotics. However, the continuing global rise in the incidence of these infections, concomitantly with the increased risk of antibiotics resistance, leads to difficulties in their control, particularly in the case of NG infections. We also discuss the potential mechanism of tumorigenesis related to CT infections. The molecular bases of CT and NG infections are addressed, as they should provide clues for control or eradication, through the development of new drugs and/or effective vaccines against these pathogens.

The role of miRNA-128 in the development and progression of gastrointestinal and urogenital cancer

Increasing data have shown the significance of various miRNAs in malignancy. In this regard, parallel to its biological role in normal tissues, miRNA-128 (miR-128) has been found to play an essential immunomodulatory function in the process of cancer initiation and development. The occurrence of the aberrant expression of miR-128 in tumors and the unique properties of miRNAs raise the prospect of their use as biomarkers and the next generation of molecular anticancer therapies. The function of miR-128 in malignancies such as breast, prostate, colorectal, gastric, pancreatic, esophageal, cervical, ovarian and bladder cancers and hepatocellular carcinoma is discussed in this review. Finally, the effect of exosomal miR-128 on cancer resistance to therapeutics and cancer immunotherapy in certain malignancies is highlighted.

Expression of RPL9 predicts the recurrence of non-muscle invasive bladder cancer with BCG therapy

Numerous biomarkers and risk tables can be used to predict recurrence or progression of patients with primary or recurrent non-muscle invasive bladder cancer (NMIBC) receiving Bacillus Calmette-Guerin (BCG). However, few are suitable for BCG-unresponsive disease (i.e., recurrence or progression after BCG treatment). Therefore, identification of a novel marker that allows accurate prediction of prognosis, particularly risk of recurrence, is critically important in clinical practice. In the current study, gene ontology and gene set enrichment analyses of microarray datasets (GSE13507, n = 47) revealed that differentially expressed genes in recurred NMIBC patients after BCG treatment were associated with virus and ribosomal pathways. Among the core-enrichment genes, the expression of RPL9, a putative tumor suppressor, was lower in recurred NMIBC patients after BCG therapy than in patients without recurrence (P = 0.033) from the E-MTAT-4321 European cohort (n = 84). Data from The Cancer Genome Atlas (n = 406) showed that bladder cancer patients with higher RPL9 expression had a longer overall survival probability than patients with lower RPL9 expression (P = 0.011). Moreover, we used the latest digital PCR platform to examine 59 NMIBC patients and identified downregulation of RPL9 in patients with recurrence after BCG therapy (P = 0.031). The Kaplan-Meier survival estimator showed that NMIBC patients with higher expression of RPL9 had longer recurrence-free survival (log-rank test, P = 0.015). Therefore, we conclude that RPL9 expression is a prospective predictor of recurrence after BCG therapy in NMIBC patients.

Gut Microbiota and Gynecological Cancers: A Summary of Pathogenetic Mechanisms and Future Directions

Over the past 20 years, important relationships between the microbiota and human health have emerged. A link between alterations of microbiota composition (dysbiosis) and cancer development has been recently demonstrated. In particular, the composition and the oncogenic role of intestinal bacterial flora has been extensively investigated in preclinical and clinical studies focusing on gastrointestinal tumors. Overall, the development of gastrointestinal tumors is favored by dysbiosis as it leads to depletion of antitumor substances (e.g., short-chain fatty acids) produced by healthy microbiota. Moreover, dysbiosis leads to alterations of the gut barrier, promotes a chronic inflammatory status through activation of toll-like receptors, and causes metabolic and hormonal dysregulations. However, the effects of these imbalances are not limited to the gastrointestinal tract and they can influence gynecological tumor carcinogenesis as well. The purpose of this Review is to provide a synthetic update about the mechanisms of interaction between gut microbiota and the female reproductive tract favoring the development of neoplasms. Furthermore, novel therapeutic approaches based on the modulation of microbiota and their role in gynecological oncology are discussed.

Epstein-Barr Virus and Human Adenovirus Viremia in Renal Tumors Is Associated with Histological Features of Malignancy

Background: There is growing evidence that viral infections may impact the risk and clinical course of malignancies, including solid tumors. The aim of this study was to assess the possible association of selected chronic/latent viral infections with the clinical course of renal cell carcinoma (RCC). Methods: In this prospective study we enrolled 27 patients undergoing partial or radical nephrectomy due to the histologically confirmed RCC and followed them up for one year post-operation. Isolation of the nucleic acids was performed using the NucleoSpin Tissue Kit (Macherey-Nagel, Düren, Germany) from tumor tissue and using the EZ1 Virus Mini Kit v2.0 from plasma. The number of viral copies of human adenovirus (ADV), herpes simplex virus HSV-1 and HSV-2, Epstein-Barr virus (EBV), cytomegalovirus (CMV), BK virus (BKV) and John Cunningham virus (JCV) in the tissue and plasma was assessed with real-time PCR. Results: Viral infections were diagnosed in ten patients (37.0%), including three ADV cases (11.1%) and eight EBV cases (29.6%). Infected patients tended to be significantly older (71.3 vs. 57.6 years, p < 0.05), more commonly presented with chronic renal disease (OR 2.4, p < 0.05), diabetes (OR 4.2, p < 0.05) and overweight (OR 2.0, p < 0.05). Regarding oncological data, infected patients were found to have a higher rate of high-grade cancers (OR 5.0, p < 0.05) and a higher rate of papillary RCCs (OR 8.3, p < 0.05). Status of viral infections had no influence on the clinical cancer stage, surgical procedure or survival. Conclusions: EBV and ADV infections are common in renal cancer patients and increase the risk of high-grade RCC presence. While there is no significant impact on short term survival, further studies are needed to assess the relevance of these findings in a long run.

Association of human papilloma virus (HPV) infection with oncological outcomes in urothelial bladder cancer

Background

Bladder cancer is one of the leading causes of cancer death in adults worldwide. There are various risk factors described for the bladder cancer development including genetic background as well as environmental exposure. Currently, infectious agents such as human papilloma virus (HPV) has also been linked to bladder cancer risk. The current study aimed to evaluate the potential correlation between HPV infection and the oncological outcome in urothelial bladder cancer.

Methods

Totally 106 tissue samples of histopathologically confirmed transitional cell carcinoma (TCC) of the urinary bladder were included in this study. The presence of high risk (types 16 and 18) and low risk (types 11 and 6) types of HPV was evaluated using polymerase chain reaction (PCR) followed by in situ hybridization.

Results

Out of 106 bladder cancer patients, a total of 24 cases (22.6%) were positive HPV infection. The most common type of HPV detected was type 16 followed by types 11 and 18, and 6. According to independent T-test results, there was a significant association between mean age and HPV infection (P = 0.015). Moreover, our findings showed a significant relation between infection with HPV and tumor stage, tumor grade, muscle invasion of the tumor, as well as tumor recurrence. The results of Chi-square Test indicated that there is significant statistical association between types of HPV and tumor grade (P-Value = 0.044).

Conclusion

Our findings indicated that a family history of cancer and HPV infection can be potential independent predictive factors for tumor recurrence in bladder cancer. Overall, the results of this study strongly indicate a significant relationship between HPV infection and an aggravated outcome of the disease and a higher risk of recurrence in patients with bladder cancer.

Factors in Oncogenesis: Viral Infections in Ovarian Cancer

Ovarian cancer (OC) is one of the leading causes of cancer death in women, with high-grade serous ovarian cancer (HGSOC) being the most lethal gynecologic malignancy among women. This high fatality rate is the result of diagnosis of a high number of new cases when cancer implants have already spread. The poor prognosis is due to our inadequate understanding of the molecular mechanisms preceding ovarian malignancy. Knowledge about the site of origination has been improved recently by the discovery of tube intraepithelial cancer (TIC), but the potential risk factors are still obscure. Due to high tumoral heterogeneity in OC, the establishment of early stage biomarkers is still underway. Microbial infection may induce or result in chronic inflammatory infection and in the pathogenesis of cancers. Microbiome research has shed light on the relationships between the host and microbiota, as well as the direct roles of host pathogens in cancer development, progression, and drug efficacy. While controversial, the detection of viruses within ovarian malignancies and fallopian tube tissues suggests that these pathogens may play a role in the development of OC. Genomic and proteomic approaches have enhanced the methods for identifying candidates in early screening. This article summarizes the existing knowledge related to the molecular mechanisms that lead to tumorigenesis in the ovary, as well as the viruses detected in OC cases and how they may elevate this process.

Comprehensive analysis of mRNA-level and miRNA-level subpathway activities for identifying robust ovarian cancer prognostic signatures

Ovarian cancer (OvCa) causes the highest mortality among all gynaecologic cancers. A large number of mRNA‐ or miRNA‐based signatures were identified for OvCa patient prognosis. However, the comprehensive analysis of function‐level prognostic signatures is currently not considered in OvCa. In the present study, we respectively inferred subpathway activities from mRNA and miRNA levels based on high‐throughput expression profiles and reconstructed subpathways. Firstly, the activities of two tumour pathways were calculated and the difference between normal and tumour samples were analysed using multiple tumour types. Then, we calculated subpathway activities for OvCa based on the expression profiles from both mRNA and miRNA levels. Furthermore, based on these subpathway activity matrices, we performed bootstrap analysis to obtain sub‐training sets and utilized univariate method to identify robust OvCa prognostic subpathways. A comprehensive comparison of subpathway results between these two levels was performed. As a result, we observed subpathway mutual exclusion trend between the levels of mRNA and miRNA, which indicated the necessary of combining mRNA‐miRNA levels. Finally, by using ICGC data as testing sets, we utilized two strategies to verify survival predictive power of the mRNA‐miRNA combined subpathway signatures and performed comparisons with results from individual levels. It was confirmed that our framework displayed application to identify robust and efficient prognostic signatures for OvCa, and the combined signatures indeed exhibited advantages over individual ones. In the study, we took a step forward in relevant novel integrated functional signatures for OvCa prognosis.

Renal Cell Carcinoma (RCC) Tumors Display Large Expansion of Double Positive (DP) CD4+CD8+ T Cells With Expression of Exhaustion Markers

Checkpoint inhibitors target the inhibitory receptors expressed by tumor-infiltrating T cells in order to reinvigorate an anti-tumor immune response. Therefore, understanding T cell composition and phenotype in human tumors is crucial. We analyzed by flow cytometry tumor-infiltrating lymphocytes (TILs) from two independent cohorts of patients with different cancer types, including RCC, lung, and colon cancer. In healthy donors, peripheral T cells are usually either CD4+ or CD8+ with a small percentage of CD4+ CD8+ DP cells (<5%). Compared to several other cancer types, including lung, and colorectal cancers, TILs from about a third of RCC patients showed an increased proportion of DP CD4+CD8+ T cells (>5%, reaching 30–50% of T cells in some patients). These DP T cells have an effector memory phenotype and express CD38, 4-1BB, and HLA-DR, suggesting antigen-driven expansion. In fact, TCR sequencing analysis revealed a high degree of clonality in DP T cells. Additionally, there were high levels of PD-1 and TIM-3 expression on DP T cells, which correlated with higher expression of PD-1 and TIM-3 in conventional single positive CD8 T cells from the same patients. These results suggest that DP T cells could be dysfunctional tumor-specific T cells with the potential to be reactivated by checkpoint inhibitors.

Distribution of Chlamydia Trachomatis Genotypes in Infective Diseases of the Female Lower Genital Tract

The purpose of this study was to investigate the distribution of Chlamydia trachomatis (CT) genotypes in infective diseases of the female lower genital tract, especially in cervical diseases.

This study included 128 CT-positive women. DNA was extracted from cervical swabs. Omp1 gene PCR-RFLP and sequencing were used to confirm the subtypes of CT. The association of subtypes with age, clinical symptoms, cervical cytology, and biopsy results was further analyzed.

Omp1 gene PCR-RFLP and sequencing showed that the order of prevalent CT genotypes in the female lower genital tract was D (n=38, 29.69%), followed by E (n=28, 21.88%), G (n=21, 16.41%), and F (n=16,12.50%). Genotypes J, H, and K were comparatively rare. Genotype I was not identified in our samples. Further analysis showed that patients with genotype G were more frequently co-infected with other bacteria. Genotype G was also associated with mucopurulent cervicitis (MPC) and cervical intraepithelial neoplasia (CIN). Patients with genotype E were commonly co-infected with HR-HPV. Although genotype D was the most prevalent, it was a relatively low-risk type.

These results provide information on distribution of CT genotypes in infective diseases of the female lower genital tract, which is instrumental to developing a vaccine for CT.

Detection of HPV genotypes and their association with p53 codon 72 polymorphism in prostate cancer

Aim: In this study, we focused on the p53 codon 72 polymorphism and HPV infections as a possible contributing factor in susceptibility to prostate cancer (PCa). Methods: Eighty histopathologically confirmed prostate biopsies comprising of 40 cancer cases and 40 benign prostate hyperplasia cases were used. Results: A significant difference was not observed between HPV presence and PCa progression. Our results showed that the p53 protein with Arg (p53-Arg72) variant contributes to the development of PCa. Conclusion: There is a near-significant association between Arg/Arg polymorphism and PCa.

High-risk HPV is not associated with epithelial ovarian cancer in a Caucasian population

Background

High-risk human papillomavirus (HPV) has been suspected to play a role in the carcinogenesis of epithelial ovarian cancer (EOC). However, results from previous studies are conflicting. In most of these studies, the number of tissue samples was small. The current study was therefore undertaken to examine the prevalence of high-risk HPV DNA in EOC in a large series of patients.

Method

Formalin-fixed, paraffin-imbedded tumor tissue samples from 198 cases consecutively included in the Danish Pelvic Mass Study were analyzed. The material included 163 serous adenocarcinomas, 15 endometrioid adenocarcinomas, 11 mucinous adenocarcinomas and nine clear-cell carcinomas. Genotyping for high-risk HPV DNA was performed by real-time Polymerase chain reaction (PCR) using an in-house TaqMan singleplex assay targeting the E6/E7 region of the HPV 16 and 18 genomes. Additionally, 20 random samples without HPV 16 and/or 18 infections were reanalyzed for HPV subtypes 31, 33, 35, 39, 45, 51 and 52.

Results

The quality criteria were fulfilled in 191 samples. HPV 18 DNA was detected in one sample only, while the rest tested negative. The subgroup analysis for seven additional high-risk HPV subtypes was also negative.

Conclusions

Only one in 191 samples was positive for HPV DNA. We therefore conclude that high risk HPV is unlikely to be associated with EOC in a Caucasian population. Future studies should focus on other microorganisms as possible etiological factors in EOC carcinogenesis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13027-016-0087-4) contains supplementary material, which is available to authorized users.

Role of the microbiome in non-gastrointestinal cancers

“The forgotten organ”, the human microbiome, comprises a community of microorganisms that colonizes various sites of the human body. Through coevolution of bacteria, archaea and fungi with the human host over thousands of years, a complex host-microbiome relationship emerged in which many functions, including metabolism and immune responses, became codependent. This coupling becomes evident when disruption in the microbiome composition, termed dysbiosis, is mirrored by the development of pathologies in the host. Among the most serious consequences of dysbiosis, is the development of cancer. As many as 20% of total cancers worldwide are caused by a microbial agent. To date, a vast majority of microbiome-cancer studies focus solely on the microbiome of the large intestine and the development of gastrointestinal cancers. Here, we will review the available evidence implicating microbiome involvement in the development and progression of non-gastrointestinal cancers, while distinguishing between viral and bacterial drivers of cancer, as well as “local” and “systemic”, “cancer-stimulating” and “cancer-suppressing” effects of the microbiome. Developing a system-wide approach to cancer-microbiome studies will be crucial in understanding how microbiome influences carcinogenesis, and may enable to employ microbiome-targeting approaches as part of cancer treatment.

Human papillomavirus 16 infection as a potential risk factor for prostate cancer: an adaptive meta-analysis

OBJECTIVES

Although an expert review published in 2013 concluded that an association between human papillomavirus (HPV) infection and prostate cancer (PCa) risk had not yet been firmly established, a 2011 systematic review of 14 articles revealed an increased prevalence of HPV-16 DNA in PCa tissues. Another meta-analysis of the related articles is needed to evaluate the potential link between HPV infection and PCa risk.

METHODS

A snowballing search strategy was applied to the previously cited articles in the above-mentioned expert review and systematic review. Additional articles selected for this meta-analysis should fulfill all following inclusion criteria: (a) evaluation of detected HPV-16 DNA in tissue samples and the PCa risk and (b) report of the HPV-16 prevalence in both cancer and control tissues. Estimated summary odds ratios (sOR) with 95% confidence intervals (CI) were calculated using fixed effect or random-effect models.

RESULTS

Hand searching identified 16 new articles. The sOR of the total 30 articles indicated a significant HPV-16 infection-related increase in the PCa risk (sOR, 1.851; 95% CI, 1.353 to 2.532, I(2)=37.82%).

CONCLUSIONS

These facts provide additional supportive evidence for a causal role of HPV-16 infection in prostate carcinogenesis. As the PCa incidence rates have increased rapidly in Asian countries, including Korea, during the last several decades, further studies of HPV-related PCa carcinogenesis may be necessary.

Multinucleation during C. trachomatis infections is caused by the contribution of two effector pathways

Chlamydia trachomatis is an obligate intracellular bacterial pathogen and the second leading cause of sexually transmitted infections in the US. Infections cause significant morbidity and can lead to serious reproductive sequelae, including an epidemiological link to increased rates of reproductive cancers. One of the overt changes that infected cells exhibit is the development of genomic instability leading to multinucleation. Here we demonstrate that the induction of multinucleation is not conserved equally across chlamydial species; C. trachomatis L2 caused high levels of multinucleation, C. muridarum intermediate levels, and C. caviae had very modest effects on multinucleation. Our data show that at least two effector pathways together cause genomic instability during infection leading to multinucleation. We find that the highly conserved chlamydial protease CPAF is a key effector for one of these pathways. CPAF secretion is required for the loss of centrosome duplication regulation as well as inducing early mitotic exit. The second effector pathway involves the induction of centrosome position errors. This function is not conserved in three chlamydial species tested. Together these two pathways contribute to the induction of high levels of genomic instability and multinucleation seen in C. trachomatis infections.

Association of Kaposi’s sarcoma-associated herpesvirus (KSHV) with bladder cancer in Croatian patients

As the seventh most common human malignancy, bladder cancer represents a global health problem. In addition to well-recognized risk factors such as smoking and exposure to chemicals, various infectious agents have been implicated as cofactors in the pathogenesis of urothelial malignancies. The aim of the present study was to assess the possible association of viral infection and bladder cancer in Croatian patients. Biopsy specimens were collected from a total of 55 patients diagnosed with different stages of bladder cancer. Initial screening of DNA extracts for the presence of viruses on Lawrence Livermore Microbial Detection Array revealed Kaposi’s sarcoma-associated herpesvirus (KSHV) in each of three randomly chosen biopsy specimens. The prevalence of infection with KSHV among study population was then examined by KSHV-specific polymerase chain reaction (PCR) and immunoblotting. By nested PCR, KSHV DNA was detected in 55% of patients. KSHV, also known as human herpesvirus 8, is an infectious agent known to cause cancer. Its oncogenic potential is primarily recognized from its role in Kaposi’s sarcoma, but it has also been involved in pathogenesis of two lymphoproliferative disorders. A high prevalence of KSHV infection in our study indicates that KSHV may play a role in tumorigenesis of bladder cancer and warrants further studies.

Tumor viruses and replicative immortality--avoiding the telomere hurdle

Tumor viruses promote cell proliferation in order to gain access to an environment suitable for persistence and replication. The expression of viral products that promote growth transformation is often accompanied by the induction of multiple signs of telomere dysfunction, including telomere shortening, damage of telomeric DNA and chromosome instability. Long-term survival and progression to full malignancy require the bypassing of senescence programs that are triggered by the damaged telomeres. Here we review different strategies by which tumor viruses interfere with telomere homeostasis during cell transformation. This frequently involves the activation of telomerase, which assures both the integrity and functionality of telomeres. In addition, recent evidence suggests that oncogenic viruses may activate a recombination-based mechanism for telomere elongation known as Alternative Lengthening of Telomeres (ALT). This error-prone strategy promotes genomic instability and could play an important role in viral oncogenesis.

Chlamydia trachomatis-infected epithelial cells and fibroblasts retain the ability to express surface-presented major histocompatibility complex class I molecules

The obligate intracellular bacterial pathogen Chlamydia trachomatis is the causative agent of a variety of infectious diseases such as trachoma and sexually transmitted diseases. In infected target cells, C. trachomatis replicates within parasitophorous vacuoles and expresses the protease-like activity factor CPAF. Previous studies have suggested that CPAF degrades the host transcription factors RFX5 and NF-κB p65, which are involved in the regulation of constitutive and inducible expression of major histocompatibility complex class I (MHC I). It was speculated that Chlamydia suppresses the surface presentation of MHC I in order to evade an effective immune response. Nevertheless, a recent study suggested that RFX5 and NF-κB p65 may not serve as target substrates for CPAF-mediated degradation, raising concerns about the proposed MHC I subversion by Chlamydia. Hence, we investigated the direct influence of Chlamydia on MHC I expression and surface presentation in infected host cells. By using nine different human cells and cell lines infected with C. trachomatis (serovar D or LGV2), we demonstrate that chlamydial infection does not interfere with expression, maturation, transport, and surface presentation of MHC I, suggesting functional antigen processing in bacterium-infected cells. Our findings provide novel insights into the interaction of chlamydiae with their host cells and should be taken into consideration for the design of future therapies and vaccines.

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.