Association between Waste Management and Cancer in Companion Animals

Environmental exposure and cancer occurrence in dogs: a critical appraisal of evidence

Cancer is a significant contributor to morbidity and mortality in humans and is also the leading cause of death in dogs. It is estimated that up to 20 % of human cancers can be explained by environmental exposures to carcinogens. It has been hypothesized that companion animals such as dogs could not only be a model for the complex pathogenic processes of human cancers, but also act as sentinels for environmental carcinogens due to their relative shorter longevity, spontaneous occurrence of tumours, and intimate relationship with our everyday environments. This review aimed to provide the epidemiological evidence on the role of the environment in the development and progression of tumours in the canine species.

Exploring risk factors linked to canine lymphoma: a case-control study

Environmental factors, largely influenced by human behavior, account for approximately 80 % of malignant tumors. Risk factors associated with non-Hodgkin's lymphoma (NHL) have been identified in various countries among both humans and domestic animals. This study aimed to investigate potential risk factors for NHL in dogs residing in the district of Porto, Portugal. A comprehensive survey comprising 70 questions was undertaken and given to 113 dog owners, including 55 cases and 58 controls. Our findings revealed that dogs weighing over 10 kg (OR=9.1, p < 0.001), purebred dogs (OR=2.4, p = 0.037), those with consuming homemade food (OR=2.7, p = 0.03), and fruits and vegetables (OR=2.8, p = 0.022) exhibited higher odds of developing lymphoma. Notably, dogs with lymphoma were exposed to a significantly higher mean smoking index compared to the control group (13.7, SD=12.5 vs. 8.4, SD=9.3, p < 0.001). These findings suggest that lymphoma risk in dogs seems to be influenced by a combination of innate (genetic) factors and modifiable environmental factors linked to owner habits. Nevertheless, further large-scale epidemiological studies are warranted to validate these results.

What We Know and Do Not Yet Know About the Canine Model of Lymphoma in Human Medicine-The Current State of Knowledge

This review comprehensively compares lymphoma in humans and dogs, highlighting the canine model's utility in translational research. Canine lymphoma (cL), predominantly diffuse large B-cell lymphoma (DLBCL), mirrors human non-Hodgkin's lymphoma (NHL) in its clinical presentation, including lymphadenopathy, systemic symptoms (e.g., fever, weight loss), and hematological abnormalities. Morphologically, cL and NHL share similarities in DLBCL subtypes (centroblastic, immunoblastic, anaplastic), although some variations exist, such as the presence of macronuclear medium-sized cells in canine polymorphonuclear centroblastic lymphoma, not observed in humans. Canine and human lymphomas share molecular mechanisms, including the activation of key pathways like NF-κB and mTOR, and genetic and epigenetic alterations. The tumor microenvironment influences tumor growth and immune evasion in both species. Both species exhibit similar responses to chemotherapy, primarily CHOP-based protocols, although canine lymphoma often progresses more rapidly, offering advantages for shorter clinical trials. Molecular targeted therapy is emerging as a promising treatment, with human therapies like rituximab and chimeric antigen receptor T-cell therapy showing efficacy, and canine treatments still developing. Epidemiological data reveal overlapping risk factors, including exposure to environmental carcinogens (e.g., household chemicals, pollution) and the potential influence of sex hormones, although the role of sex hormones requires further investigation in canines. While staging systems differ slightly (Lugano modification of Ann Arbor for humans, WHO system for dogs), both consider disease extent and systemic involvement. Prognostic factors, such as lactate dehydrogenase (LDH) levels, are relevant in human NHL but have not shown consistent utility in cL. This study concludes that the spontaneous development of cL in immunocompetent dogs, coupled with its clinical, histological, and therapeutic similarities to human NHL, makes the canine model invaluable for preclinical research, accelerating the development of novel diagnostic tools and therapies for both human and canine lymphoma. The shared environmental risk factors and shorter disease progression in dogs further enhance the translational potential of this model, promoting a One Health approach to cancer research.

Canine on the Couch: The New Canary in the Coal Mine for Environmental Health Research

Human health is intimately connected and tied to the health of our environment and ecosystem, with only a very small fraction of the risk for chronic diseases explained by genetics alone. Companion animals are prone to disease types that are shared with people, including cancers and endocrine disorders, reinforcing the thought that environmental factors contribute to the risks for chronic diseases. These factors include air and water pollution and the built environment. As such, there is increasing interest in pursuing research with companion animals, and specifically dogs, as sentinel species to inform comparative health assessments and identify risk factors for disease. Of the canine diseases for which environmental exposure research has been published, cancers have received the most attention. This review summarizes two main aspects of this comparative approach: (1) cancers that occur in dogs and which are similar to humans and (2) research investigating environmental exposures and health outcomes in dogs. The goal of this review is to highlight the diverse conditions in which pet dogs may provide unique perspectives and advantages to examine relationships between environmental exposures and health outcomes, with an emphasis on chemical pollution and cancer. Furthermore, this review seeks to raise awareness and stimulate discussion around the best practices for the use of companion animals as environmental health sentinels.

Environmental radon, fracking wells, and lymphoma in dogs

BACKGROUND

Multicentric lymphoma (ML) in dogs resembles non-Hodgkin lymphoma (NHL) in humans. Human NHL is associated with multiple environmental exposures, including to radon and volatile organic compounds (VOCs).

HYPOTHESIS/OBJECTIVES

The objective of this study was to determine whether ML in dogs was associated with environmental radon or proximity to horizontal oil and drilling (fracking), a source of VOC pollution.

METHODS

We identified dogs from the Golden Retriever Lifetime Study that developed ML (n = 52) along with matched controls (n = 104). Dog home addresses were categorized by Environmental Protection Agency radon zone and average residential radon by county, as well as by distance from fracking and associated wastewater wells.

RESULTS

We found no significant differences in county level radon measurements. Individual household radon measurements were not available. There was no difference in residential proximity to active fracking wells between dogs with ML and unaffected dogs. While dogs with ML lived closer to wastewater wells (123 vs 206 km; P = .01), there was no difference in the percentage of cases vs controls that lived in close proximity (20 km) to a fracking well (11.5% for cases, 6.7% for controls; OR 1.81, 95% CI 0.55 to 5.22; P = .36), or a wastewater well (6.7% for cases, 4.4% for controls; P > .99).

CONCLUSIONS AND CLINICAL IMPORTANCE

These data suggest that more proximate sources of chemical exposures need to be assessed in dogs with ML, including measurements of individual household radon and household VOC concentrations.

Mortality and heavy metals environmental exposure: a study in dogs

Introduction

Dogs are human companions and share environmental conditions with their owners. Epidemiological studies have shown that dogs seem to be good sentinel animals for the association of diseases and/or mortality provoked by chronic exposure to heavy metals (Cd, Pb).

Methods

In the present work, we analyze the registered death cases and population from the National Canine Registry from 2020 to 2022, involving a dog population of 582,564 and 17,507 deaths. The mortality rate in male and not-purebred dogs is higher than in female and purebred dogs, respectively. The mortality cases were cross-referenced with the environmental pollution data relating to the concentration of Cd and Pb detected, between 2012 and 2022, in the various municipalities of the Liguria region. We then calculated SMR (Standardized Mortality Rate) throughout the region and found that mortality increases from the eastern to the western Ligurian coast.

Results and discussion

We observed that the most polluted areas present the highest SMRs (IRR = 1.36, 95%CI: from 1.31 to 1.41). Considering dog ages, we found that mortality in young dogs is not affected by pollution, while mortality in old dogs (10-20 years old) is heavily affected by it (IRR = 8.97, 95%CI from 8.09 to 9.93). In conclusion, the data suggest the importance of canine health and biomonitor studies and provide a basis for future research involving both animal and human health.

Lymphoma in Border Collies: Genome-Wide Association and Pedigree Analysis

There has been considerable interest in studying cancer in dogs and its potential as a model system for humans. One area of research has been the search for genetic risk variants in canine lymphoma, which is amongst the most common canine cancers. Previous studies have focused on a limited number of breeds, but none have included Border Collies. The aims of this study were to identify relationships between Border Collie lymphoma cases through an extensive pedigree investigation and to utilise relationship information to conduct genome-wide association study (GWAS) analyses to identify risk regions associated with lymphoma. The expanded pedigree analysis included 83,000 Border Collies, with 71 identified lymphoma cases. The analysis identified affected close relatives, and a common ancestor was identified for 54 cases. For the genomic study, a GWAS was designed to incorporate lymphoma cases, putative "carriers", and controls. A case-control GWAS was also conducted as a comparison. Both analyses showed significant SNPs in regions on chromosomes 18 and 27. Putative top candidate genes from these regions included DLA-79, WNT10B, LMBR1L, KMT2D, and CCNT1.

Dog Models of Aging

As the most phenotypically diverse mammalian species that shares human environments and access to sophisticated healthcare, domestic dogs have unique potential to inform our understanding of the determinants of aging. Here we outline key concepts in the study of aging and illustrate the value of research with dogs, which can improve dog health and support translational discoveries. We consider similarities and differences in aging and age-related diseases in dogs and humans and summarize key advances in our understanding of genetic and environmental risk factors for morbidity and mortality in dogs. We address health outcomes ranging from cancer to cognitive function and highlight emerging research opportunities from large-scale cohort studies in companion dogs. We conclude that studying aging in dogs could overcome many limitations of laboratory models, most notably, the ability to assess how aging-associated pathways influence aging in real-world environments similar to those experienced by humans.

Why We Will Continue to Lose Our Battle with Cancers If We Do Not Stop Their Triggers from Environmental Pollution

Besides our current health concerns due to COVID-19, cancer is a longer-lasting and even more dramatic pandemic that affects almost a third of the human population worldwide. Most of the emphasis on its causes has been posed on genetic predisposition, chance, and wrong lifestyles (mainly, obesity and smoking). Moreover, our medical weapons against cancers have not improved too much during the last century, although research is in progress. Once diagnosed with a malignant tumour, we still rely on surgery, radiotherapy, and chemotherapy. The main problem is that we have focused on fighting a difficult battle instead of preventing it by controlling its triggers. Quite the opposite, our knowledge of the links between environmental pollution and cancer has surged from the 1980s. Carcinogens in water, air, and soil have continued to accumulate disproportionally and grow in number and dose, bringing us to today's carnage. Here, a synthesis and critical review of the state of the knowledge of the links between cancer and environmental pollution in the three environmental compartments is provided, research gaps are briefly discussed, and some future directions are indicated. New evidence suggests that it is relevant to take into account not only the dose but also the time when we are exposed to carcinogens. The review ends by stressing that more dedication should be put into studying the environmental causes of cancers to prevent and avoid curing them, that the precautionary approach towards environmental pollutants must be much more reactionary, and that there is an urgent need to leave behind the outdated petrochemical-based industry and goods production.

Genetic and environmental risk for lymphoma in boxer dogs

BACKGROUND

Non-Hodgkin lymphoma in humans is associated with environmental chemical exposures, and risk is enhanced by genetic variants in glutathione S-transferases (GST) enzymes.

OBJECTIVE

We hypothesized that boxer dogs, a breed at risk for lymphoma, would have a higher prevalence of GST variants with predicted low activity, and greater accumulated DNA damage, compared to other breeds. We also hypothesized that lymphoma in boxers would be associated with specific environmental exposures and a higher prevalence of canine GST variants.

ANIMALS

Fifty-four healthy boxers and 56 age-matched nonboxer controls; 63 boxers with lymphoma and 89 unaffected boxers ≥10 years old.

METHODS

We resequenced variant loci in canine GSTT1, GSTT5, GSTM1, and GSTP1 and compared endogenous DNA damage in peripheral leukocytes of boxers and nonboxers using the comet assay. We also compared GST variants and questionnaire-based environmental exposures in boxers with and without lymphoma.

RESULTS

Endogenous DNA damage did not differ between boxers and nonboxers. Boxers with lymphoma were more likely to live within 10 miles of a nuclear power plant and within 2 miles of a chemical supplier or crematorium. Lymphoma risk was not modulated by known canine GST variants.

CONCLUSIONS AND CLINICAL IMPORTANCE

Proximity to nuclear power plants, chemical suppliers, and crematoria were significant risk factors for lymphoma in this population of boxers. These results support the hypothesis that aggregate exposures to environmental chemicals and industrial waste may contribute to lymphoma risk in dogs.

Comparative Exposure Assessment Using Silicone Passive Samplers Indicates That Domestic Dogs Are Sentinels To Support Human Health Research

Silicone wristbands are promising passive samplers to support epidemiological studies in characterizing exposure to organic contaminants; however, investigating associated health risks remains challenging because of the latency period for many chronic diseases that take years to manifest. Dogs provide valuable insights as sentinels for exposure-related human disease because they share similar exposures in the home, have shorter life spans, share many clinical/biological features, and have closely related genomes. Here, we evaluated exposures among pet dogs and their owners using silicone dog tags and wristbands to determine if contaminant levels were correlated with validated exposure biomarkers. Significant correlations between measures on dog tags and wristbands were observed (r_s = 0.38-0.90; p < 0.05). Correlations with their respective urinary biomarkers were stronger in dog tags compared to that in human wristbands (r_s = 0.50-0.71; p < 0.01) for several organophosphate esters. This supports the value of using silicone bands with dogs to investigate health impacts on humans from shared exposures.

Exploring Uncertainty in Canine Cancer Data Sources Through Dasymetric Refinement

In spite of the potentially groundbreaking environmental sentinel applications, studies of canine cancer data sources are often limited due to undercounting of cancer cases. This source of uncertainty might be further amplified through the process of spatial data aggregation, manifested as part of the modifiable areal unit problem (MAUP). In this study, we explore potential explanatory factors for canine cancer incidence retrieved from the Swiss Canine Cancer Registry (SCCR) in a regression modeling framework. In doing so, we also evaluate differences in statistical performance and associations resulting from a dasymetric refinement of municipal units to their portion of residential land. Our findings document severe underascertainment of cancer cases in the SCCR, which we linked to specific demographic characteristics and reduced use of veterinary care. These explanatory factors result in improved statistical performance when computed using dasymetrically refined units. This suggests that dasymetric mapping should be further tested in geographic correlation studies of canine cancer incidence and in future comparative studies involving human cancers.

Immunocytochemical study of canine lymphomas and its correlation with exposure to tobacco smoke

Aim:

Canine lymphoma is one of the most common canine neoplasms, but little is known regarding the effects of exposure to tobacco smoke on their biologic behavior. As cytology is the most frequent diagnostic method of canine lymphoma, the aims of this study were to perform an immunocytochemical study of canine lymphomas, including subtyping and cell proliferation analysis, and to establish their correlation with tobacco smoke exposure.

Materials and Methods:

A total of 23 dogs diagnosed with lymphoma were subjected to careful fine-needle biopsies of enlarged lymph nodes. The smears were air-dried, fixed with cold acetone, and immunocytochemically stained using CD3, PAX5, and Ki-67. Owners were requested to complete an epidemiologic questionnaire.

Results:

According to the updated Kiel classification, 65% were B-cell lymphomas - three low grade (LG) and 12 high grade (HG) and 35% were T-cell -two LG and six HG. Thirteen tumors presented high Ki67 indexes (>40%) (11 HG and 2 LG), two revealed moderate ones (20-40%) (1 HG and 1 LG), and three had low indexes (≤20%) (1 HG and 2 LG). Both a significant positive correlation and a significant linear-by-linear association (p=0.018) were observed between high Ki67 indexes and smoking owners (r=0.753, p=0.002) as well as with the number of smokers in the household (r=0.641, p=0.001). Moreover, the mean percentage of Ki67⁺ cells from the group of “smoker owners” was statically higher (p=0.011) than that from the “non-smoker owners.”

Conclusion:

The results suggest that cytological diagnosis of canine lymphomas benefits from being complemented with immunocytochemical studies that include subtyping and assessment of proliferative activity, both contributing for the prognosis and therapeutic planning. Furthermore, exposure to tobacco smoke seems to be related to the biological behavior of canine lymphomas.

Characterization of a low expression haplotype in canine glutathione S-transferase (GSTT1) and its prevalence in golden retrievers

Glutathione S-transferase-theta (GSTT1) is a carcinogen detoxification enzyme, and low activity variants are associated with lymphoma in humans. We recently found a variant in the 3' untranslated region (UTR) of canine GSTT1, *101_102insT, which was predicted to change miRNA binding and was found in 5 of 17 golden retriever (GR) dogs with lymphoma but none of 14 healthy GRs. The aim of this study was to determine whether this variant led to decreased GSTT1 expression and was a discernible risk factor for lymphoma within the GR breed. On resequencing, *101_102insT appeared to be in complete linkage disequilibrium with 3 additional 3'UTR variants, leading to the inferred haplotype *3T>C; *101_102insT; *190C>A; *203T>C. In canine livers that were heterozygous for this variant haplotype, GSTT1 protein expression was significantly lower compared to the reference haplotype (densitometry .40 vs .64, P = .022), and GSTT1 transcript levels by qPCR were also significantly lower (fold difference .52, P = .012), without evidence of substantial allelic expression imbalance. The variant haplotype led to >50% decrease in expression in vitro (.31 ± .07 vs .64 ± .19; P = .019). We found no significant difference in minor allele frequencies between 71 GR dogs with lymphoma (MAF .162) and 33 healthy age-matched controls (MAF .136, P = .69). Our results indicate that the variant GSTT1 3'UTR haplotype containing *101_102insT reduces gene expression, which could lead to impaired carcinogen detoxification, but was not a detectable risk factor for lymphoma in GR dogs.

The evidence of toxic wastes dumping in Campania, Italy

The region of Campania (particularly Naples and Caserta) were subjected to extensive illegal dumping operations of toxic and radioactive wastes since the 1980s. The highly toxic wastes (HTW) dumping operations that have taken place both along the coast and the hinterland, have extremely adverse effects on health, livelihoods and the future prospect of sustainable development of the local population. The toxic wastes dumping in Campania is real and it has compromised (irreversibly) the human health, natural environment, food security and the long-term development prospects of the affected population. To reverse this tragic trend, it is necessery the identification, isolation and reclamation of the polluted sites and full assessment of the nature and the scale of the polluting chemicals and other hazardous wastes. The purpose of this review is to contribute significantly to the available evidence of the long-running toxic waste dumping in Campania and its negative impact on the health of population.

[Multicentric lymphoma in 411 dogs - an epidemiological study]

OBJECTIVE

To provide an overview of the epidemiology of canine multicentric lymphoma in Germany.

MATERIAL AND METHODS

A total of 411 dogs with multicentric malignant lymphoma were retrospectively analysed regarding breed, age, sex, weight and the number of animals dogs with hypercalcaemic lymphoma and B-/T-immunophenotype, and compared to two reference populations (total own clinic population, n   =   52  142; dogs with health insurance in Germany, n   =   123  423).

RESULTS

In total, 298 (72.5%) of the 411 dogs belonged to 86 different breeds, while 113 (27.5%) dogs were mixed breed. In comparison to both reference populations, a breed predisposition for the American Pitbull Terrier (odds ratio [OR] 5.2 and 18.5), American Staffordshire Terrier (OR 3.3 and 4.6), Briard (OR 5.6 and 9.5), Bullmastiff (OR 7.8 and 5.0), Irish Setter (OR 3.3 and 4.1) and Rottweiler (OR 2.8 and 3.6) was found. Golden Retrievers (n = 22, OR 1.3 and 0.9) and Bernese Mountain Dogs (n = 22, OR 2.4 and 2.0) were frequently affected in absolute numbers, but when compared to the reference populations an OR < 3 was detected. Mean body weight was 30.2 ± 13.7 kg; only 75 (18%) dogs weighed < 15 kg. Amongst the small dogs (< 15 kg), there was a large number of West Highland White Terriers (n = 12). Mean age of the dogs with lymphoma was 7.9 ± 2.7 years. Dogs weighing ≥ 15 kg were significantly (p < 0.001) younger (7.6 ± 2.4 years) compared to dogs weighing < 15 kg (9.3 ± 3.2 years). Dogs with a B-cell immunophenotype (8.5 ± 2.6 years) were significantly older compared to dogs with a T-cell immunophenotype (6.4 ± 1.8 years) (p < 0.001). There was no gender predisposition (54% male, 46% female). Hypercalcaemia as an indicator of T-cell lymphoma was present in 44 (11.4%) of the dogs. A T-cell and B-cell immunophenotype was found in 20.6% and 79.4% of the dogs, respectively.

CLINICAL RELEVANCE

This study confirms previous data about breed predispositions for canine malignant multicentric lymphoma and demonstrates that further breeds are predisposed (Briard, West Highland White Terrier, Irish Setter). Small-breed dogs (< 15 kg BM) appear to be affected with lymphoma at a greater age.

Biology and Diseases of Dogs

Historically, the dog played an important role as a laboratory animal in biomedical research. Although numbers are declining, the use of dogs continues to be common in pharmacokinetics and cardiovascular studies. The normal biology of the dog as both a laboratory and a companion animal has been well studied and reference values are presented here as a clinical and experimental resource. This provides the necessary background to discuss the spontaneous diseases, including infectious and neoplastic conditions, prevalent in purpose bred as well as random source dogs used in biomedical research. In addition, diseases and conditions that arise secondary to the housing and experimental manipulation of dogs is discussed with emphasis on treatment and prevention.

The dog as a possible animal model for human non-Hodgkin lymphoma: a review

Lymphoma represents the most frequent hematopoietic cancer in dogs, and it shows significant overlap with the human disease. Several environmental factors have been associated with canine lymphoma, suggesting that they may contribute to lymphomagenesis. Canine lymphoma often presents in advanced stage (III-V) at diagnosis and, most commonly, has an aggressive clinical course requiring prompt treatment, which relies on the use of polychemotherapy. In this review, we will summarize the state-of-the-art of canine lymphoma epidemiology, pathobiology, diagnostic work-up and therapy, and will highlight the links to the corresponding human disease, providing evidence for the use of dog as an animal model of spontaneous disease.

The staging and treatment of multicentric high-grade lymphoma in dogs: a review of recent developments and future prospects

In recent years, considerable progress has been made in understanding the biology of canine lymphoma with resultant enhanced classification schemes and the possibility of individualised, tailored therapies. However, although complete remission may be achieved using multi-agent chemotherapy, the mortality rate from this neoplasm remains high. This review focuses on the staging of high-grade multicentric lymphoma in the dog, on conventional and novel treatment strategies (including chemotherapy, bone marrow transplantation, radiation therapy and molecular-targeted agents), and on the management of relapsed or refractory cases.

Identification of suitable endogenous controls and differentially expressed microRNAs in canine fresh-frozen and FFPE lymphoma samples

The elucidation of microRNA (miRNA) expression pattern in canine lymphoma is attractive for veterinary and comparative oncology due to similar genetics, physiology and exposure to environment in dogs and humans. In this work, the expression of a panel of mature miRNAs was quantitated in fresh-frozen and formalin-fixed paraffin-embedded (FFPE) lymph nodes from canine lymphoma. The major findings were: the detection of a panel of miRNAs expressed in canine lymph node; the identification of three suitable endogenous controls (let-7a, miR-16, and miR-26b) by NormFinder and geNorm analysis; the concordance between results obtained from fresh-frozen and FFPE samples; the detection of upregulation of miR-17-5p and miR-181a in B- and T-cell lymphomas respectively. This is the first study aimed to the application of miRNAs analysis in canine lymphoma.