Residential road traffic and railway noise and risk of childhood cancer: A nationwide register-based case-control study in Denmark

BACKGROUND

The aetiology of most childhood cancers remains poorly understood. We conducted a nationwide register-based case-control study to assess the association between residential road traffic and railway noise exposure and risk of childhood cancers.

METHODS

We identified all cases of first cancers diagnosed in children aged 0-19 years in 1985-2013 from the Danish Cancer Registry (N = 3962) and sampled four individually matched (by sex and date of birth) controls per case (N = 14,790) using the Central Population Register. We estimated time-weighted exposure averages of residential road traffic and railway noise at the most (Lden max) and least (Lden min) exposed façades from birth to index-date (for additional analysis: in utero period) based on the individual address history for the respective time windows. We fitted conditional logistic regression models to estimate odds ratios (OR) and their 95% confidence intervals (CI).

RESULTS

ORs varied by noise estimate and cancer type, with generally wide CIs mostly including 1.00. We found a tendency of higher ORs with increasing railway and road traffic noise for Hodgkin lymphoma (ORs for railway and road Lden min were 1.63 (95% CI 1.00; 2.66) and 1.14 (95% CI 0.87; 1.48) per 10 dB), as well as a tendency of higher ORs with increasing railway noise for non-Hodgkin lymphoma. For embryonal CNS tumours and astrocytoma and other glioma we observed also some weak suggestions of a positive association. Analysing exposure to traffic noise in utero revealed similar patterns to those of the main analyses.

CONCLUSIONS

This nationwide study with minimal risk of bias suggests no strong associations between traffic noise and risk of most childhood cancers. We found however some suggestive evidence for a positive association with Hodgkin lymphoma, non-Hodgkin lymphoma and some CNS tumours. Further research is warranted to confirm these associations in other populations and elucidate the underlying biological mechanisms.

Bovine Meat and Milk Factors (BMMFs): Their Proposed Role in Common Human Cancers and Type 2 Diabetes Mellitus

Simple Summary

This manuscript emphasizes the mechanistic differences of infectious agents contributing to human cancers either by “direct” or “indirect” interactions. The epidemiology of cancers linked to direct carcinogens differs (e.g., response to immunosuppression) from those cancers linked with indirect infectious interactions. We discuss their role in colon, breast, and prostate cancers and type II diabetes mellitus. A brief discussion covers the potential role of BMMF (bovine meat and milk factor) infections in acute myeloid leukemia.

Abstract

Exemplified by infections with bovine meat and milk factors (BMMFs), this manuscript emphasizes the different mechanistic aspects of infectious agents contributing to human cancers by “direct” or “indirect” interactions. The epidemiology of cancers linked to direct carcinogens (e.g., response to immunosuppression) differs from those cancers linked with indirect infectious interactions. Cancers induced by direct infectious carcinogens commonly increase under immunosuppression, whereas the cancer risk by indirect carcinogens is reduced. This influences their responses to preventive and therapeutic interferences. In addition, we discuss their role in colon, breast and prostate cancers and type II diabetes mellitus. A brief discussion covers the potential role of BMMF infections in acute myeloid leukemia.

Family history of any cancer for childhood leukemia patients in Sweden

Acute lymphoblastic leukemia (ALL) is the most common childhood leukemia, while the other types, acute myeloid leukemia (AML), chronic lymphocytic leukemia (CLL), and chronic myeloid leukemia (CML) are much rarer. While data on familial risks for childhood ALL have been emerging, such data for the other childhood leukemias are hardly available. We aim to fill in the gap of knowledge by assessing familial clustering of each childhood leukemia with childhood and adult leukemia and with any cancer. We identified 4461 childhood leukemias from the Swedish Cancer Registry and obtained their family members from the Multigeneration Register. Standardized incidence ratios (SIRs) were 3.34 for singleton siblings both diagnosed with ALL before age 20 years and 1.64 for those who had a family member diagnosed with ALL in adult age. Other childhood leukemias showed no familial risk, but childhood ALL risk was increased to 1.40 when adult family members were diagnosed with CLL. Childhood ALL was associated with endometrial cancer, and female ALL patients showed increased risk when family members were diagnosed with testicular cancer, melanoma, and skin squamous cell carcinoma. Childhood CLL was associated with rectal cancer, and childhood AML was associated with pancreatic and bladder cancers. As most of these associations are reported for the first time, there is a need to replicate the findings from independent sources.

The glycosphingolipid GD2 as an effective but enigmatic target of passive immunotherapy in children with aggressive neuroblastoma (HR-NBL)

Neuroblastoma (NBL), the most frequent and lethal pediatric cancer of children in pre-school age, is considered enigmatic in view of its extreme heterogeneity, from spontaneous regression in the IV-S form to incurable disease in approx. 40% of cases (High Risk, HR-NBL). It has an embryonal origin and a very heterogeneous genomic landscape, hampering the success of targeted strategies. The glycosphingolipid GD2 was shown to be expressed on NBL cells and utilized as target for passive immunotherapy with anti-GD2 antibodies (GD2-IMT). An international protocol was established with GD2-IMT, which increases remission length and survival in HR-NBL. By reviewing the different biological and molecular aspects of NBL and GD2-IMT, this mini-review questions the present lack of association between GD2-IMT and the underlying molecular landscape. The alternative model of Micro-Foci inducing virus (MFV) is presented, since MFV infection can induce extensive genomic aberrations (100X NMYC DNA-amplification). Since this family of viruses uses molecules for cell penetration similar to GD2 (i.e., GM2), it is hypothesized that GD2 is the port-of-entry for MFV and that success of anti-GD2 therapies is also associated to inhibition of this clastogenic virus in HR-NBL.

Increased Risk of Chronic Myeloid Leukemia Following Gastric Conditions Indicating Helicobacter pylori Infection: A Case-Control Study

BACKGROUND

On the basis of a previous report of increased chronic myeloid leukemia (CML) risk following peptic ulcer, we hypothesized that chronic Helicobacter pylori infection could serve as a risk factor for CML.

METHODS

In a population-based, retrospective case-control study, we used Swedish registry data on 980 patients with CML and 4,960 age- and sex-matched controls to investigate associations between markers of previous infection with Helicobacter pylori and CML incidence.

RESULTS

Previous diagnoses of dyspepsia, gastritis or peptic ulcers, as well as previous proton pump inhibitor (PPI) medication, were all associated with a significantly increased risk of CML (RRs, 1.5-2.0; P = 0.0005-0.05). Meanwhile, neither inflammatory bowel disease nor intake of NSAIDs were associated with CML, indicating that it is not gastrointestinal ulcer or inflammation per se that influences risk.

CONCLUSIONS

The consistent associations suggest a shared background between gastric conditions and CML, and strengthen the case that Helicobacter pylori could constitute this common risk factor.

IMPACT

As the etiology of CML is practically unknown, and Helicobacter pylori could potentially be a therapeutic target, even this indirect evidence encourages further studies on the potential involvement of Helicobacter pylori in CML etiology.

Childhood infectious diseases and risk of non-Hodgkin's lymphoma according to the WHO classification: A reanalysis of the Italian multicenter case-control study

Since 1960, incidence of non-Hodgkin's lymphoma (NHL) has been increasing in most industrialized countries, but causes of this trend remain unclear. A role of the decreased exposure to infectious agents during childhood has been proposed. Our study evaluates the association between common childhood infectious diseases and the risk of NHL and its major subtypes by a reanalysis of the Italian multicenter case-control study. After exclusion of next-of-kin interviews, 1,193 cases, diagnosed between 1990 and 1993, and 1,708 population-based controls were included in the analyses. OR estimates were obtained by logistic regression, adjusting for gender, age, residence area, education, smoking habit and exposure to radiations, pesticides and aromatic hydrocarbons. Among B-cell lymphomas (n = 1,102) an inverse association was observed for rubella (OR = 0.80, 95% CI: 0.65-0.99), pertussis (OR = 0.74, 95% CI: 0.62-0.88) and any infection (OR = 0.75, 95% CI: 0.61-0.93). A negative trend by number of infections was observed, which was more evident among mature B-cell lymphoma (OR = 0.66 for three infections or more, 95% CI: 0.48-0.90). Our results indicate a potential protective role of common childhood infections in the etiology of B-cell NHL.

ICRP Publication 131: Stem Cell Biology with Respect to Carcinogenesis Aspects of Radiological Protection

This report provides a review of stem cells/progenitor cells and their responses to ionising radiation in relation to issues relevant to stochastic effects of radiation that form a major part of the International Commission on Radiological Protection's system of radiological protection. Current information on stem cell characteristics, maintenance and renewal, evolution with age, location in stem cell 'niches', and radiosensitivity to acute and protracted exposures is presented in a series of substantial reviews as annexes concerning haematopoietic tissue, mammary gland, thyroid, digestive tract, lung, skin, and bone. This foundation of knowledge of stem cells is used in the main text of the report to provide a biological insight into issues such as the linear-no-threshold (LNT) model, cancer risk among tissues, dose-rate effects, and changes in the risk of radiation carcinogenesis by age at exposure and attained age. Knowledge of the biology and associated radiation biology of stem cells and progenitor cells is more developed in tissues that renew fairly rapidly, such as haematopoietic tissue, intestinal mucosa, and epidermis, although all the tissues considered here possess stem cell populations. Important features of stem cell maintenance, renewal, and response are the microenvironmental signals operating in the niche residence, for which a well-defined spatial location has been identified in some tissues. The identity of the target cell for carcinogenesis continues to point to the more primitive stem cell population that is mostly quiescent, and hence able to accumulate the protracted sequence of mutations necessary to result in malignancy. In addition, there is some potential for daughter progenitor cells to be target cells in particular cases, such as in haematopoietic tissue and in skin. Several biological processes could contribute to protecting stem cells from mutation accumulation: (a) accurate DNA repair; (b) rapidly induced death of injured stem cells; (c) retention of the DNA parental template strand during divisions in some tissue systems, so that mutations are passed to the daughter differentiating cells and not retained in the parental cell; and (d) stem cell competition, whereby undamaged stem cells outcompete damaged stem cells for residence in the niche. DNA repair mainly occurs within a few days of irradiation, while stem cell competition requires weeks or many months depending on the tissue type. The aforementioned processes may contribute to the differences in carcinogenic radiation risk values between tissues, and may help to explain why a rapidly replicating tissue such as small intestine is less prone to such risk. The processes also provide a mechanistic insight relevant to the LNT model, and the relative and absolute risk models. The radiobiological knowledge also provides a scientific insight into discussions of the dose and dose-rate effectiveness factor currently used in radiological protection guidelines. In addition, the biological information contributes potential reasons for the age-dependent sensitivity to radiation carcinogenesis, including the effects of in-utero exposure.

Childhood acute lymphoblastic leukemia and indicators of early immune stimulation: a Childhood Leukemia International Consortium study

The associations between childhood acute lymphoblastic leukemia (ALL) and several proxies of early stimulation of the immune system, that is, day-care center attendance, birth order, maternally reported common infections in infancy, and breastfeeding, were investigated by using data from 11 case-control studies participating in the Childhood Leukemia International Consortium (enrollment period: 1980-2010). The sample included 7,399 ALL cases and 11,181 controls aged 2-14 years. The data were collected by questionnaires administered to the parents. Pooled odds ratios and 95% confidence intervals were estimated by unconditional logistic regression adjusted for age, sex, study, maternal education, and maternal age. Day-care center attendance in the first year of life was associated with a reduced risk of ALL (odds ratio = 0.77, 95% confidence interval: 0.71, 0.84), with a marked inverse trend with earlier age at start (P < 0.0001). An inverse association was also observed with breastfeeding duration of 6 months or more (odds ratio = 0.86, 95% confidence interval: 0.79, 0.94). No significant relationship with a history of common infections in infancy was observed even though the odds ratio was less than 1 for more than 3 infections. The findings of this large pooled analysis reinforce the hypothesis that day-care center attendance in infancy and prolonged breastfeeding are associated with a decreased risk of ALL.

Target-dependent enrichment of virions determines the reduction of high-throughput sequencing in virus discovery

Viral infections cause many different diseases stemming both from well-characterized viral pathogens but also from emerging viruses, and the search for novel viruses continues to be of great importance. High-throughput sequencing is an important technology for this purpose. However, viral nucleic acids often constitute a minute proportion of the total genetic material in a sample from infected tissue. Techniques to enrich viral targets in high-throughput sequencing have been reported, but the sensitivity of such methods is not well established. This study compares different library preparation techniques targeting both DNA and RNA with and without virion enrichment. By optimizing the selection of intact virus particles, both by physical and enzymatic approaches, we assessed the effectiveness of the specific enrichment of viral sequences as compared to non-enriched sample preparations by selectively looking for and counting read sequences obtained from shotgun sequencing. Using shotgun sequencing of total DNA or RNA, viral targets were detected at concentrations corresponding to the predicted level, providing a foundation for estimating the effectiveness of virion enrichment. Virion enrichment typically produced a 1000-fold increase in the proportion of DNA virus sequences. For RNA virions the gain was less pronounced with a maximum 13-fold increase. This enrichment varied between the different sample concentrations, with no clear trend. Despite that less sequencing was required to identify target sequences, it was not evident from our data that a lower detection level was achieved by virion enrichment compared to shotgun sequencing.

Reprint of: cancer "causation" by infections--individual contributions and synergistic networks

The search for infectious agents playing a role in human carcinogenesis and their identification remain important issues. This could provide clues for a broader spectrum of cancers preventable by vaccination and accessible to specific therapeutic regimens. Yet, the various ways of interacting among different factors functioning synergistically and their different modes of affecting individual cells should bring to question the validity of the term "causation". It also should put a word of caution into all attempts to summarize criteria for "causality" of infectious agents in cancer development. At least in the opinion of these authors, we would be much better off avoiding these terms, replacing "causal factor" by "risk factor" and grading them according to their contribution to an individual's cancer risk.

Cancer "causation" by infections--individual contributions and synergistic networks

The search for infectious agents playing a role in human carcinogenesis and their identification remain important issues. This could provide clues for a broader spectrum of cancers preventable by vaccination and accessible to specific therapeutic regimens. Yet, the various ways of interacting among different factors functioning synergistically and their different modes of affecting individual cells should bring to question the validity of the term "causation". It also should put a word of caution into all attempts to summarize criteria for "causality" of infectious agents in cancer development. At least in the opinion of these authors, we would be much better off avoiding these terms, replacing "causal factor" by "risk factor" and grading them according to their contribution to an individual's cancer risk.

Virus infection and human cancer: an overview

It is now estimated that approximately 10 % of worldwide cancers are attributable to viral infection, with the vast majority (>85 %) occurring in the developing world. Oncogenic viruses include various classes of DNA and RNA viruses and induce cancer by a variety of mechanisms. A unifying theme is that cancer develops in a minority of infected individuals and only after chronic infection of many years duration. The viruses associated with the greatest number of cancer cases are the human papillomaviruses (HPVs), which cause cervical cancer and several other epithelial malignancies, and the hepatitis viruses HBV and HCV, which are responsible for the majority of hepatocellular cancer. Other oncoviruses include Epstein-Barr virus (EBV), Kaposi's sarcoma-associated herpes virus (KSHV), human T-cell leukemia virus (HTLV-I), and Merkel cell polyomavirus (MCPyV). Identification of the infectious cause has led to several interventions that may reduce the risk of developing these tumors. These include preventive vaccines against HBV and HPV, HPV-based testing for cervical cancer screening, anti-virals for the treatment of chronic HBV and HCV infection, and screening the blood supply for the presence of HBV and HCV. Successful efforts to identify additional oncogenic viruses in human cancer may lead to further insight into etiology and pathogenesis as well as to new approaches for therapeutic and prophylactic intervention.

Childhood cancers: what is a possible role of infectious agents?

The etiology of childhood cancers has been studied for more than 40 years. However, most if not all cancers occurring in children are attributed to unknown causes. This review is focused on the role of infections in cancer development and progression in children. The main infectious agents include human herpesviruses, polyoma viruses, and human papilloma viruses. It is known that infections can lead to carcinogenesis through various mechanisms, and most likely act in addition to genetic and environmental factors. Given the importance of the infectious etiology of childhood cancers, clinical implications and possible prevention strategies are discussed.

Sensitive detection of viral transcripts in human tumor transcriptomes

In excess of % of human cancer incidents have a viral cofactor. Epidemiological studies of idiopathic human cancers indicate that additional tumor viruses remain to be discovered. Recent advances in sequencing technology have enabled systematic screenings of human tumor transcriptomes for viral transcripts. However, technical problems such as low abundances of viral transcripts in large volumes of sequencing data, viral sequence divergence, and homology between viral and human factors significantly confound identification of tumor viruses. We have developed a novel computational approach for detecting viral transcripts in human cancers that takes the aforementioned confounding factors into account and is applicable to a wide variety of viruses and tumors. We apply the approach to conducting the first systematic search for viruses in neuroblastoma, the most common cancer in infancy. The diverse clinical progression of this disease as well as related epidemiological and virological findings are highly suggestive of a pathogenic cofactor. However, a viral etiology of neuroblastoma is currently contested. We mapped transcriptomes of neuroblastoma as well as positive and negative controls to the human and all known viral genomes in order to detect both known and unknown viruses. Analysis of controls, comparisons with related methods, and statistical estimates demonstrate the high sensitivity of our approach. Detailed investigation of putative viral transcripts within neuroblastoma samples did not provide evidence for the existence of any known human viruses. Likewise, de-novo assembly and analysis of chimeric transcripts did not result in expression signatures associated with novel human pathogens. While confounding factors such as sample dilution or viral clearance in progressed tumors may mask viral cofactors in the data, in principle, this is rendered less likely by the high sensitivity of our approach and the number of biological replicates analyzed. Therefore, our results suggest that frequent viral cofactors of metastatic neuroblastoma are unlikely.

Many human cancers are caused by infections with tumor viruses and identification of these pathogens is considered a critical contribution to cancer prevention. Deep sequencing enables us to systematically investigate viral nucleotide signatures in order to either verify or exclude the existence of viruses in idiopathic human cancers. We have developed Virana, a novel computational approach for identifying tumor viruses in human cancers that is applicable to a wide variety of tumors and viruses. Virana firstly addresses several important biological confounding factors that may hinder successful detection of these pathogens. We applied our approach in the first systematic search for cancer-causing viruses in metastatic neuroblastoma, the most common form of cancer in infancy. Although the heterogeneous clinical progression of this disease as well as epidemiological and virological findings are suggestive of a pathogenic cofactor, the viral etiology of neuroblastoma is currently contested. We conducted an analysis of experimental controls, comparisons with related approaches, as well as statistical analyses in order to validate our method. In spite of the high sensitivity of our approach, analyses of neuroblastoma transcriptomes did not provide evidence for the existence of any known or unknown human viruses. Our results therefore suggest that frequent viral cofactors of metastatic neuroblastoma are unlikely.

Multiple infections and cancer: implications in epidemiology

Approximately 18% of the global cancer burden has been attributed to infectious agents, with estimates ranging from 7% in developed countries to about 22% in developing countries. Chronic infections caused by the hepatitis B and C viruses, human papilloma viruses (HPV), and Helicobacter pylori (H. pylori) are reported to be responsible for approximately 15% of all human cancers. Interestingly, although many of the infectious agents that have been associated with cancer--such as HPV, Epstein-Barr virus (EBV), and H. pylori--are highly prevalent in the world, most infected individuals do not develop cancer but remain lifelong carriers. Malignancies associated with infectious agents may result from prolonged latency as a result of chronic infections. Pathogenic infections are necessary but are not sufficient for cancer initiation or progression. Cancer initiation may require additional cofactors, including secondary infections. Therefore, in patients with chronic infection with one agent, secondary co-infection with another agent may serve as an important co-factor that may cause cancer initiation and progression. Additionally, opportunistic co-infections could significantly inhibit response to cancer treatment and increase cancer mortality. Co-infections are relatively common in areas with a high prevalence of infectious agents, especially in developing countries. These co-infections can cause an imbalance in the host immune system by affecting persistence of and susceptibility to malignant infections. Several articles have been published that focus on infectious agents and cancer. In this article, we discuss the role of infectious agents in malignancies, highlight the role of multiple/co-infections in cancer etiology, and review implications for cancer epidemiology.

The human virome: new tools and concepts

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New sequencing technologies increase our knowledge regarding the composition of the human virome.

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There are beneficial and detrimental viruses.

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The human virome can impact upon health at body surfaces (skin or gut) and within tissues.

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Some animal viruses are transmitted via the oral route by consumption of food.

The human virome is the viral component of the microbiome. Its composition, and interindividual and temporal variability are not precisely known. Its impact on human health has received less attention than that of the bacterial microbiome, but is likely to be equally important, both in homeostasis and disease. Here we review the recent advances in this field and the questions that arise in the context of our rapidly increasing knowledge regarding the composition and function of the human virome. With the ever-extending use of next-generation sequencing (NGS) on a variety of clinical samples, rapid progress on the composition of the human virome and its impact upon human health are to be expected in the coming years.

Childhood infectious diseases and risk of leukaemia in an adult population

Our study is aimed at investigating the association between common childhood infectious diseases (measles, chickenpox, rubella, mumps and pertussis) and the risk of developing leukaemia in an adult population. A reanalysis of a large population-based case-control study was carried out. Original data included 1,771 controls and 649 leukaemia cases from 11 Italian areas. To contain recall bias, the analysis was restricted to subjects directly interviewed and with a good quality interview (1,165 controls and 312 cases). Odds ratios (ORs) and their related 95% confidence intervals (95% CIs) were estimated by unconditional polychotomous logistic regression model adjusting for age, gender and occupational and lifestyle exposures. A protective effect of at least one infection (OR = 0.66, 95% CI: 0.45-0.97), measles (OR = 0.57, 95% CI: 0.39-0.82) and pertussis (OR = 0.66, 95% CI: 0.45-0.98) was observed for chronic lymphoid leukaemia (CLL). The number of infections was strongly inversely associated with the risk of CLL (p = 0.002, test for trend). With regard to the other types of leukaemia, only a protective effect of pertussis was observed for AML (OR = 0.52, 95% CI: 0.32-0.87). Our results pointed out a protective role of childhood infectious diseases on the risk of CLL in adults. Although a specific antioncogenic effect of some infectious disease, especially measles, cannot be ruled out, the observed decrease of risk with increasing number of infections suggests that a more general "hygiene hypothesis" could be the most likely explanation of the detected association. The protective role of pertussis remains to be elucidated.

Familial risks for childhood acute lymphocytic leukaemia in Sweden and Finland: far exceeding the effects of known germline variants

Despite recent successes in the identification of genetic susceptibility loci, no familial risk has been demonstrated for childhood acute lymphoblastic leukaemia (ALL). We identified 3994 childhood ALL cases from two cancer registries; family members were obtained from population registers. The standardized incidence ratio for familial risk in singleton siblings and twins was 3·2 (95% confidence interval 1·5-5·9) and 162·6 (70·2-320·4), respectively. The present data constitute the first demonstration of familial risk for singleton siblings; the high risk for twins is believed to result from shared prenatal blood circulation. The data suggest that currently unidentified genetic loci underlie these observed familial effects.

Co-morbidity between early-onset leukemia and type 1 diabetes--suggestive of a shared viral etiology?

Background

Acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML) are common early-onset malignancies. Their causes are largely unknown but infectious etiology has been implicated. Type 1 diabetes (T1D) is an autoimmune disease for which infectious triggers of disease onset have been sought and increasing pointing to enteroviruses. Based on our previous results on co-morbidity between leukemia and T1D, we updated the Swedish dataset and focused on early onset leukemias in patients who had been hospitalized for T1D, comparing to those not hospitalized for T1D.

Methods and Findings

Standardized incidence ratios (SIRs) were calculated for leukemia in 24,052 patients hospitalized for T1D covering years 1964 through 2008. T1D patients were included if hospitalized before age 21 years. Practically all Swedish children and adolescents with T1D are hospitalized at the start of insulin treatment. SIR for ALL was 8.30 (N = 18, 95% confidence interval 4.91–13.14) when diagnosed at age 10 to 20 years after hospitalization for T1D and it was 3.51 (13, 1.86–6.02) before hospitalization for T1D. The SIR for ALL was 19.85 (N = 33, 13.74–27.76) and that for AML was 25.28 (8, 10.80–50.06) when the leukemias were diagnosed within the year of T1D hospitalization. The SIRs increased to 38.97 (26, 25.43–57.18) and 40.11 (8, 17.13–79.42) when T1D was diagnosed between ages 10 to 20 years. No consistent time-dependent changes were found in leukemia risk.

Conclusion

A shared infectious etiology could be a plausible explanation to the observed co-morbidity. Other possible contributing factors could be insulin therapy or T1D related metabolic disturbances.

Epstein-Barr virus stimulates torque teno virus replication: a possible relationship to multiple sclerosis

Viral infections have been implicated in the pathogenesis of multiple sclerosis. Epstein-Barr virus (EBV) has frequently been investigated as a possible candidate and torque teno virus (TTV) has also been discussed in this context. Nevertheless, mechanistic aspects remain unresolved. We report viral replication, as measured by genome amplification, as well as quantitative PCR of two TTV-HD14 isolates isolated from multiple sclerosis brain in a series of EBV-positive and -negative lymphoblastoid and Burkitt's lymphoma cell lines. Our results demonstrate the replication of both transfected TTV genomes up to day 21 post transfection in all the evaluated cell lines. Quantitative amplification indicates statistically significant enhanced TTV replication in the EBV-positive cell lines, including the EBV-converted BJAB line, in comparison to the EBV-negative Burkitt's lymphoma cell line BJAB. This suggests a helper effect of EBV infections in the replication of TTV. The present study provides information on a possible interaction of EBV and TTV in the etiology and progression of multiple sclerosis.

Viral infections and human cancers: the legacy of Denis Burkitt

Denis Parsons Burkitt was born in 1911, and in the late 1950s, described the disease that has come to be known as Burkitt lymphoma based on cases he observed in Uganda. Subsequently, Burkitt lymphoma was recognized as the first human tumour associated with an infectious agent when Epstein-Barr virus was isolated from samples supplied by Burkitt. It is now recognized that over one-quarter of cancers worldwide are tied to infections. Notably, liver cancer is linked to hepatitis B virus and hepatitis C virus infections, and cervical cancer to infections involving the human papilloma viruses. In addition, immunocompromise arising from infection with the human immunodeficiency virus allows tumours (e.g., Kaposi sarcoma) caused by other viruses to arise. More than 50 years after the seminal paper by Burkitt based on his work in Africa, it is appreciated that the contribution of viral infections to cancers remains considerably higher in sub-Saharan Africa than in the rest of the world.

Influence of family size and birth order on risk of cancer: a population-based study

BACKGROUND

Family size and birth order are known to influence the risk of some cancers. However, it is still unknown whether these effects change from early to later adulthood. We used the data of the Swedish Family-Cancer Database to further analyze these effects.

METHODS

We selected over 5.7 million offspring with identified parents but no parental cancer. We estimated the effect of birth order and family size by Poisson regression adjusted for age, sex, period, region and socioeconomic status. We divided the age at diagnosis in two groups, below and over 50 years, to identify the effect of family size and birth order for different age periods.

RESULTS

Negative associations for increasing birth order were found for endometrial, testicular, skin, thyroid and connective tissue cancers and melanoma. In contrast, we observed positive association between birth order and lung, male and female genital cancers. Family size was associated with decreasing risk for endometrial and testicular cancers, melanoma and squamous cell carcinoma; risk was increased for leukemia and nervous system cancer. The effect of birth order decreased for lung and endometrial cancer from age at diagnosis below to over 50 years. Combined effects for birth order and family size were marginally significant for thyroid gland tumors. Especially, the relative risk for follicular thyroid gland tumors was significantly decreased for increasing birth order.

CONCLUSION

Our findings suggest that the effect of birth order decreases from early to late adulthood for lung and endometrial cancer.

Cancer risk among patients hospitalized for Type 1 diabetes mellitus: a population-based cohort study in Sweden

AIMS

Type 1 diabetes mellitus (T1DM) is an autoimmune disease with potential mechanistic links to immune-related cancers. We aimed at examining the overall and specific cancer risks among hospitalized T1DM patients from the national registers in Sweden.

METHODS

A T1DM research cohort was created by identifying T1DM patients from the Hospital Discharge Register and linking them with the Cancer Registry. Standardized incidence ratios (SIRs) for subsequent cancers were calculated among patients with T1DM compared with those without T1DM.

RESULTS

Two hundred and fifty-eight cases were ascertained with subsequent cancers during the follow-up duration from 1964 to 2006, with an increased overall SIR of 1.17 (95% CI 1.04-1.33) among 24 052 T1DM patients identified at baseline. Significant excess was noted for gastric and skin (squamous cell carcinoma) cancers and for leukaemia. Increased risk of acute lymphatic leukaemia accounted for most of the variation of leukaemia risk (SIR = 5.31, 95% CI 3.32-8.05). Cancer risk varied with sex, age at first hospitalization and numbers of hospitalizations. The risk was higher in women compared with men and in those hospitalized for T1DM at age over 10 years compared with the younger patients. Higher risks were also found among those with more hospital visits.

CONCLUSION

By quantifying the variations of overall and site-specific cancer risks after T1DM, the current study provides novel associations between T1DM and subsequent cancers, the mechanisms of which remain to be established.

The search for infectious causes of human cancers: where and why

Slightly more than 20% of the global cancer burden can presently be linked to infectious agents, including viruses, bacteria and parasites. This manuscript analyzes reasons for their relatively late discovery and highlights epidemiological observations that may point to an involvement of additional infectious agents in specific human cancers. Emphasis is placed on hematopoietic malignancies, breast and colorectal cancers, but also basal cell carcinomas of the skin and lung cancers in non-smokers.