Cancer Face Research Articles

Molecular characterization of Cryptosporidium and Giardia from the Tasmanian devil (Sarcophilus harrisii).

The Tasmanian devil (Sarcophilus harrisii) is a carnivorous marsupial found only in the wild in Tasmania, Australia. Tasmanian devils are classified as endangered and are currently threatened by devil facial tumour disease, a lethal transmissible cancer that has decimated the wild population in Tasmania. To prevent extinction of Tasmanian devils, conservation management was implemented in 2003 under the Save the Tasmanian Devil Program. This study aimed to assess if conservation management was altering the interactions between Tasmanian devils and their parasites. Molecular tools were used to investigate the prevalence and diversity of two protozoan parasites, Cryptosporidium and Giardia, in Tasmanian devils. A comparison of parasite prevalence between wild and captive Tasmanian devils showed that both Cryptosporidium and Giardia were significantly more prevalent in wild devils (p < 0.05); Cryptosporidium was identified in 37.9% of wild devils but only 10.7% of captive devils, while Giardia was identified in 24.1% of wild devils but only 0.82% of captive devils. Molecular analysis identified the presence of novel genotypes of both Cryptosporidium and Giardia. The novel Cryptosporidium genotype was 98.1% similar at the 18S rDNA to Cryptosporidium varanii (syn. C. saurophilum) with additional samples identified as C. fayeri, C. muris, and C. galli. Two novel Giardia genotypes, TD genotype 1 and TD genotype 2, were similar to G. duodenalis from dogs (94.4%) and a Giardia assemblage A isolate from humans (86.9%). Giardia duodenalis BIV, a zoonotic genotype of Giardia, was also identified in a single captive Tasmanian devil. These findings suggest that conservation management may be altering host-parasite interactions in the Tasmanian devil, and the presence of G. duodenalis BIV in a captive devil points to possible human-devil parasite transmission.

Relict or reintroduction? Genetic population assignment of three Tasmanian devils (Sarcophilus harrisii) recovered on mainland Australia.

Today, the Tasmanian devil (Sarcophilus harrisii) is found only on the island of Tasmania, despite once being widespread across mainland Australia. While the devil is thought to have become extinct on the mainland approximately 3000 years ago, three specimens were collected in Victoria (south-eastern Australia) between 1912 and 1991, raising the possibility that a relict mainland population survived in the area. Alternatively, these devils may have escaped captivity or were deliberately released after being transported from Tasmania, a practice that has been strictly controlled since the onset of devil facial tumour disease in the early 1990s. Such quarantine regimes are important to protect disease-free, ‘insurance populations’ in zoos on the mainland. To test whether the three Victorian devils were members of a relict mainland population or had been recently transported from Tasmania we identified seven single nucleotide polymorphisms (SNPs) in the mitochondrial genome that can distinguish between Tasmanian and ancient mainland populations. The three Victorian devil specimens have the same seven SNPs diagnostic of modern Tasmanian devils, confirming that they were most likely transported from Tasmania and do not represent a remnant population of mainland devils.

Variants in the host genome may inhibit tumour growth in devil facial tumours: evidence from genome-wide association

Devil facial tumour disease (DFTD) has decimated wild populations of Tasmanian devils (Sarcophilus harrisii) due to its ability to avoid immune detection and pass from host to host by biting. A small number of devils have been observed to spontaneously recover from the disease which is otherwise fatal. We have sequenced the genomes of these rare cases and compared them to the genomes of devils who succumbed to the disease. Genome-wide association, based on this limited sampling, highlighted two key genomic regions potentially associated with ability to survive DFTD. Following targeted genotyping in additional samples, both of these loci remain significantly different between cases and controls, with the PAX3 locus retaining significance at the 0.001 level, though genome-wide significance was not achieved. We propose that PAX3 may be involved in a regulatory pathway that influences the slowing of tumour growth and may allow more time for an immune response to be mounted in animals with regressed tumours. This provides an intriguing hypothesis for further research and could provide a novel route of treatment for this devastating disease.

Possible mechanisms of transmissible cancers in Tasmanian devils

Abstract Physical transfer of viable tumor cells from one organism to another is known as transmissible cancer, which is observed in dogs, Tasmanian devils, Syrian hamsters, and some soft-shell clams. Tasmanian devil facial tumor disease is transmitted like an infectious disease between individuals through biting and other close contact. This extinction type is quite different from the other extinction types such as ecological factors. Transmissible cancers’ cellular metabolism is also different from the both normal cellular metabolism and other types of cancers’ metabolism. The lack of an immune response against the Tasmanian devil facial tumor cells is the one of the key points in the transmission of the cancerous cells. The differentiated cellular metabolism and absence of immune reaction may be due to the organisms’ enzymes. Cells may have altered surface proteins by altering enzymatic activities that cannot be recognized by both the innate and adaptive responses. The promiscuity of the key enzymes may be associated with unwanted side effects, such as cannot recognize molecular patterns on the transmitted cell or hypomethylation of DNA by altering catalytic properties enzymes or altered matrix metalloproteinases or cathelicidins.

Significant decline in anticancer immune capacity during puberty in the Tasmanian devil

Tasmanian devils (Sarcophilus harrisii) are at risk of extinction in the wild due to Devil Facial Tumour Disease (DFTD), a rare contagious cancer. The prevalence of DFTD differs by age class: higher disease prevalence is seen in adults (2–3 years) versus younger devils (<2 years). Here we propose that immunological changes during puberty may play a role in susceptibility to DFTD. We show that the second year of life is a key developmental period for Tasmanian devils, during which they undergo puberty and pronounced changes in the immune system. Puberty coincides with a significant decrease in lymphocyte abundance resulting in a much higher neutrophil:lymphocyte ratio in adults than subadults. Quantitative PCR analysis of gene expression of transcription factors T-bet and GATA-3 and cytokines interferon gamma (IFN-γ) and interleukin 4 (IL-4) revealed a drastic increase in GATA-3 and IL-4 expression during puberty. These changes led to a significantly lower IFN-γ:IL-4 ratio in 2-year-olds than <1 year olds (on average 1.3-fold difference in males and 4.0-fold in females), which reflects a major shift of the immune system towards Th2 responses. These results all indicate that adult devils are expected to have a lower anticancer immune capacity than subadults, which may explain the observed pattern of disease prevalence of DFTD in the wild.

Regression of devil facial tumour disease following immunotherapy in immunised Tasmanian devils

Devil facial tumour disease (DFTD) is a transmissible cancer devastating the Tasmanian devil (Sarcophilus harrisii) population. The cancer cell is the ‘infectious’ agent transmitted as an allograft by biting. Animals usually die within a few months with no evidence of antibody or immune cell responses against the DFTD allograft. This lack of anti-tumour immunity is attributed to an absence of cell surface major histocompatibility complex (MHC)-I molecule expression. While the endangerment of the devil population precludes experimentation on large experimental groups, those examined in our study indicated that immunisation and immunotherapy with DFTD cells expressing surface MHC-I corresponded with effective anti-tumour responses. Tumour engraftment did not occur in one of the five immunised Tasmanian devils, and regression followed therapy of experimentally induced DFTD tumours in three Tasmanian devils. Regression correlated with immune cell infiltration and antibody responses against DFTD cells. These data support the concept that immunisation of devils with DFTD cancer cells can successfully induce humoral responses against DFTD and trigger immune-mediated regression of established tumours. Our findings support the feasibility of a protective DFTD vaccine and ultimately the preservation of the species.

Conservation implications of limited genetic diversity and population structure in Tasmanian devils (Sarcophilus harrisii).

Tasmanian devils face a combination of threats to persistence, including Devil Facial Tumor Disease (DFTD), an epidemic transmissible cancer. We used RAD sequencing to investigate genome-wide patterns of genetic diversity and geographic population structure. Consistent with previous results, we found very low genetic diversity in the species as a whole, and we detected two broad genetic clusters occupying the northwestern portion of the range, and the central and eastern portions. However, these two groups overlap across a broad geographic area, and differentiation between them is modest (FST = 0.1081). Our results refine the geographic extent of the zone of mixed ancestry and substructure within it, potentially informing management of genetic variation that existed in pre-diseased populations of the species. DFTD has spread across both genetic clusters, but recent evidence points to a genomic response to selection imposed by DFTD. Any allelic variation for resistance to DFTD may be able to spread across the devil population under selection by DFTD, and/or be present as standing variation in both genetic regions.

Immune-endocrine interactions in marsupials and monotremes

Interactions between the immune and endocrine systems are not well studied in marsupials and monotremes. One exception to this is the phenomenon of semelparity, which is well covered in the literature as this is an unusual reproductive strategy amongst mammals and is only observed in some dasyurid and didelphid marsupials. Thymus involution provides a direct link between the endocrine and immune systems and warrants further study in marsupials and monotremes. The thymus is a primary immune tissue which is essential for overall immune function. Whilst the organ is large in juvenile animals, it begins to involute around puberty due to the suppressive effects of sex steroids. Thymus involution has a significant effect on the immune system, as it signals the onset of immune aging and decline in function. The output of naïve T lymphocytes by the thymus decreases, increasing susceptibility of aged individuals to infection and cancers. Understanding the links between the immune and endocrine system in marsupials and monotremes may shed light on diseases such as devil facial tumour disease (DFTD) which threatens the future of the Tasmanian devil. We hypothesise that changes in sex hormones around puberty may drive changes in the immune system, such as thymus involution, which may make devils more susceptible to DFTD as they age. In addition, the Schwann cell origin of DFTD may enable tumours to respond to sex hormones, as occurs in similar cancers in humans.

Age-Structured and Vaccination Models of Devil Facial Tumor Disease

Age-Structured and Vaccination Models of Devil Facial Tumor Disease

The Immunomodulatory Small Molecule Imiquimod Induces Apoptosis in Devil Facial Tumour Cell Lines.

The survival of the Tasmanian devil (Sarcophilus harrisii) is threatened by devil facial tumour disease (DFTD). This transmissible cancer is usually fatal, and no successful treatments have been developed. In human studies, the small immunomodulatory molecule imiquimod is a successful immunotherapy, activating anti-tumour immunity via stimulation of toll-like receptor-7 (TLR7) signaling pathways. In addition, imiquimod is a potent inducer of apoptosis in human tumour cell lines via TLR7 independent mechanisms. Here we investigate the potential of imiquimod as a DFTD therapy through analysis of treated DFTD cell lines and Tasmanian devil fibroblasts. WST-8 proliferation assays and annexin V apoptosis assays were performed to monitor apoptosis, and changes to the expression of pro- and anti-apoptotic genes were analysed using qRT-PCR. Our results show that DFTD cell lines, but not Tasmanian devil fibroblasts, are sensitive to imiquimod-induced apoptosis in a time and concentration dependent manner. Induction of apoptosis was accompanied by down-regulation of the anti-apoptotic BCL2 and BCLXL genes, and up-regulation of the pro-apoptotic BIM gene. Continuous imiquimod treatment was required for these effects to occur. These results demonstrate that imiquimod can deregulate DFTD cell growth and survival in direct and targeted manner. In vivo, this may increase DFTD vulnerability to imiquimod-induced TLR7-mediated immune responses. Our findings have improved the current knowledge of imiquimod action in tumour cells for application to both DFTD and human cancer therapy.

PD-L1 Is Not Constitutively Expressed on Tasmanian Devil Facial Tumor Cells but Is Strongly Upregulated in Response to IFN-γ and Can Be Expressed in the Tumor Microenvironment.

The devil facial tumor disease (DFTD) is caused by clonal transmissible cancers that have led to a catastrophic decline in the wild Tasmanian devil (Sarcophilus harrisii) population. The first transmissible tumor, now termed devil facial tumor 1 (DFT1), was first discovered in 1996 and has been continually transmitted to new hosts for at least 20 years. In 2015, a second transmissible cancer [devil facial tumor 2 (DFT2)] was discovered in wild devils, and the DFT2 is genetically distinct and independent from the DFT1. Despite the estimated 136,559 base pair substitutions and 14,647 insertions/deletions in the DFT1 genome as compared to two normal devil reference genomes, the allograft tumors are not rejected by the host immune system. Additionally, genome sequencing of two sub-strains of DFT1 detected greater than 15,000 single-base substitutions that were found in only one of the DFT1 sub-strains, demonstrating the transmissible tumors are evolving and that generation of neoantigens is likely ongoing. Recent evidence in human clinical trials suggests that blocking PD-1:PD-L1 interactions promotes antitumor immune responses and is most effective in cancers with a high number of mutations. We hypothesized that DFTD cells could exploit the PD-1:PD-L1 inhibitory pathway to evade antitumor immune responses. We developed recombinant proteins and monoclonal antibodies (mAbs) to provide the first demonstration that PD-1 binds to both PD-L1 and PD-L2 in a non-placental mammal and show that PD-L1 is upregulated in DFTD cells in response to IFN-γ. Immunohistochemistry showed that PD-L1 is rarely expressed in primary tumor masses, but low numbers of PD-L1+ non-tumor cells were detected in the microenvironment of several metastatic tumors. Importantly, in vitro testing suggests that PD-1 binding to PD-L1 and PD-L2 can be blocked by mAbs, which could be critical to understanding how the DFT allografts evade the immune system.

Nutritional status and functional digestive histology of the carnivorous Tasmanian devil (Sarcophilus harrisii)

Tasmanian devils (Sarcophilus harrisii) are the largest carnivorous marsupial in Australia. Currently many animals are being held in captivity as a management procedure to combat Devil Facial Tumor Disease. Only one published study thus far has investigated nutrition in Tasmanian devils, determining their maintenance energy requirements and digestibility on a rodent diet. More information is needed on Tasmanian devil nutritional and gastrointestinal function to aid in their management. Our study aimed to investigate the current nutritional status of Tasmanian devils in a captive population and functional morphology and histology of their gastrointestinal tract. Animals were maintained on a diet of kangaroo, rabbit, quail and chicken wings and digestibility of these items by the devils was high (>85% for dry matter, protein and lipid). Kangaroo and rabbit were high protein diet items while the quail and chicken wings provided high lipid to the diet, and carbohydrates were minimal (≤3% energy). Maintenance energy requirements were determined to be 620kJkg−0.75d−1 with no significant difference between males and females. Opportunistic samples for gastrointestinal morphology were obtained from captive specimens. Tasmanian devils have a simple digestive tract similar to other dasyurid species. Both the morphology and histology of the gastrointestinal tract show specialization for a high protein carnivorous diet.

A review of parasites in the Tasmanian devil (Sarcophilus harrisii)

Threatened by devil facial tumour disease, the Tasmanian devil (Sarcophilus harrisii), a carnivorous marsupial confined to Tasmania, Australia, is the subject of conservation management under the Save the Tasmanian Devil Program. Conservation actions such as captive breeding and translocation may impact upon parasite ecology, presenting risk of increased disease through stress and impaired immunity, and by exposing hosts to parasites to which they are immunologically naive. Given the importance of parasites to ecosystem function, it has been argued from a biodiversity perspective that parasites should be conserved in their own right. In this review we describe current knowledge, and limitations in our knowledge, of Tasmanian devil parasites. We then discuss the potential for changes in host–parasite interactions as a result of host-population decline and conservation management, both generally and with examples from the Tasmanian devil. The review closes with a recommendation for a systematic evaluation of parasites in captive and wild devils to aid conservation of this host–parasite system in its entirety.

Abstract B040: Imiquimod initiates tumor specific overload of the ER stress response in Tasmanian devil facial cancer cells

Abstract Background: The potent immune modifier imiquimod (R-837) induces apoptosis of various tumor cell lines by mechanisms that are not fully understood. As a topical immunotherapy, imiquimod successfully activates tumor-specific cytotoxic responses via stimulation of TLR7 signaling pathways and antagonism of adenosine receptor mediated regulatory pathways. A role for imiquimod-induced tumor apoptosis in augmenting this response has not been defined, however it remains plausible that molecular changes may render the cells more susceptible to an anti-tumor response. An improved understanding of the pathways regulated by imiquimod in tumor cells will reveal whether this is likely the case. Devil facial tumor disease (DFTD) is a clonal transmissible cancer threatening the world's largest marsupial carnivore, the Tasmanian devil. DFTD evades both non-self and anti-cancer immune defenses to survive in new hosts, providing an ideal model for studying immunotherapeutic mechanisms. As we have previously shown that DFTD cells are sensitive to treatment with imiquimod, investigation of these effects could reveal new therapeutic strategies for DFTD, and will improve our understanding of this drug in cancer immunotherapy. Methods: To investigate the mechanisms of imiquimod action in tumor cells, DFTD cell lines and control fibroblast cell lines were treated in culture with imiquimod. Changes to cell viability were monitored by proliferation and cell death assays. Molecular changes to DFTD cells were assessed through RNA sequencing and proteomic mass spectrometry, and bioinfomatic techniques were employed to identify biological processes regulated by imiquimod. Major findings were confirmed by quantitative PCR. Results: Imiquimod treatment induces complete apoptosis of DFTD cells, but not fibroblasts, over a period of days. Transcriptomic and proteomic analysis revealed high constitutive expression of ER stress genes in DFTD cell lines, which were further augmented in response to imiquimod treatment. Up-regulation of genes required for ER-stress mediated apoptosis was also detected, suggesting that imiquimod induces apoptosis through exhaustion of the ER stress response. Molecular pathways associated with tumor growth and survival were modulated in the dying cells, and damage-associated alarmins were highly expressed. Conclusions: Our study provides the first whole transcriptome and proteome analysis of any imiquimod treated tumor cell line. By using DFTD cells as a tumor model, we have shown that imiquimod directly increases the apoptotic potential of tumor cells through augmentation of ER stress, while producing molecular changes consistent with reduced tumorigenicity. These effects were not replicated in fibroblasts, suggesting that constitutive activation of stress responses in tumor cells may impact their ability to cope with additional stressors. Our findings suggest that ER stress pathways are ideal targets for therapy against DFTD in our endangered Tasmanian devil. These data can also be applied for more rational use of imiquimod as an immunotherapeutic agent in human cancer. Citation Format: Amanda L. Patchett, Terry L. Pinfold, Cesar Tovar, Bruce Lyons, Gregory M. Woods. Imiquimod initiates tumor specific overload of the ER stress response in Tasmanian devil facial cancer cells [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr B040.

Metapopulation management of an Endangered species with limited genetic diversity in the presence of disease: the Tasmanian devil Sarcophilus harrisii

There has been much discussion relating to the current biodiversity crisis, with the loss of species now at an unprecedented rate. Using augmentation and/or reintroduction to minimize the loss of species in the wild is becoming more prominent. Zoological institutions have been traditionally involved in the management of insurance populations providing a range of species for release to the wild. Insurance populations can be costly, both in resources and behavioural changes, and so should aim to be maintained for as short a time as possible, with a maximum of 40 years. A Tasmanian devil Sarcophilus harrisii insurance population was established in 2006 with the arrival of devil facial tumour disease, and was founded with 120 individuals sourced predominantly from the west coast of Tasmania. Here the challenges of establishing and managing an insurance population in an already genetically depauperate species in the presence of a contagious cancer are discussed. The Tasmanian devil insurance metapopulation now includes a continuum of management scenarios (from intensive zoo‐based facilities, through free‐range enclosures, to an island and fenced peninsula) and consists of over 700 devils representing at least 180 founders. The lessons learned in regard to this programme are presented, including the issues surrounding reduced genetic diversity and how we are striving to improve the long‐term management of the insurance metapopulation through a combination of molecular genetics, modelling and on‐the‐ground management. The tools and technologies that have been developed in this programme are directly applicable to the recovery and management of a suite of other threatened fauna.

Demonstration of immune responses against devil facial tumour disease in wild Tasmanian devils.

Devil facial tumour disease (DFTD) is a recently emerged fatal transmissible cancer decimating the wild population of Tasmanian devils (Sarcophilus harrisii). Biting transmits the cancer cells and the tumour develops in the new host as an allograft. The literature reports that immune escape mechanisms employed by DFTD inevitably result in host death. Here we present the first evidence that DFTD regression can occur and that wild devils can mount an immune response against the disease. Of the 52 devils tested, six had serum antibodies against DFTD cells and, in one case, prominent T lymphocyte infiltration in its tumour. Notably, four of the six devils with serum antibody had histories of DFTD regression. The novel demonstration of an immune response against DFTD in wild Tasmanian devils suggests that a proportion of wild devils can produce a protective immune response against naturally acquired DFTD. This has implications for tumour–host coevolution and vaccine development.

Discovery of Biomarkers for Tasmanian Devil Cancer (DFTD) by Metabolic Profiling of Serum.

Devil facial tumor disease (DFTD) is a transmissible cancer threatening Tasmanian devils (Sarcophilus harrisii) with extinction. There is no preclinical test available for DFTD, and thus our aim was to find biomarkers for DFTD by metabolic fingerprinting. Seventy serum samples from wild Tasmanian devils (35 controls, 35 with tumors) were analyzed by liquid chromatography-high-resolution mass spectrometry. Features were selected by multivariate models (PLS/DA, random forests) comparing age-matched training set (n = 20 × 2) and further complying with fold-change threshold (≥1.4) and Mann-Whitney U-tests with correction for multiple hypotheses (false discovery rate (FDR) q < 0.05). An array of overlapping peptide segments of the N-terminal end of fibrinogen were the strongest positive DFTD markers. These peptides recorded fold-change up to 90, FDR-corrected p value below 0.01, and area under ROC curve of at least 0.80 and also correlated with tumor size (Spearman R > 0.45, p < 0.01). Additional potential markers included amino acid and lipid metabolites, while cortisol and urea were the most significant health predictors (AUC ≥ 0.90). PLS/DA resulted in AUC = 0.997 for the training set and overall sensitivity of 91% and specificity of 97%. A support vector machine model utilizing only the major peptide marker and seven other metabolites led to overall 94% sensitivity and specificity. The novel findings in this first DFTD metabolomics study shed light on metabolic changes in Tasmanian devils affected by DFTD and provide a valuable step toward the development of prognostic biomarkers.

Hematologic and serum biochemical changes associated with Devil Facial Tumor Disease in Tasmanian Devils.

Devil Facial Tumor Disease (DFTD) is an infectious tumor causing significant population declines in wild Tasmanian Devils. While clinical assessment and pathology have been well reported for DFTD, there is a lack of information on hematologic and biochemical alterations associated with DFTD. The purpose of the study was to determine hematologic and serum biochemical variation in healthy, wounded, and DFTD-affected Tasmanian Devils. Blood samples were collected from wild Tasmanian Devils at 5 sites in Tasmania. Hematology and clinical biochemistry variables were compared between clinically healthy, wounded, and DFTD-affected devils. Differences were also analyzed among stages of DFTD, including individuals pre- and postclinical signs developing, and between ulcerated and nonulcerated DFTD tumors. Statistically significantly increased counts in WBC, neutrophils, and platelets, and concentration of fibrinogen, as well as decreased counts in lymphocytes, erythrocytes, and HGB concentration were observed in DFTD-affected devils compared to healthy devils. Activities of ALP, ALT, and GLDH, concentrations of sodium, potassium and albumin, and sodium-to-potassium ratio and albumin-to-globulin ratio were significantly lower, and AST activity was significantly higher in animals with DFTD when compared to clinically healthy animals. No significant differences were found among stages of DFTD or ulcerated and nonulcerated tumors. The differences in hematology and clinical chemistry variables in devils with DFTD compared to healthy devils are nonspecific and reflective of acute phase response and inflammation, and anemia of chronic disease. Similar changes are observed with wounds but to a lesser extent.

Rapid evolutionary response to a transmissible cancer in Tasmanian devils.

Although cancer rarely acts as an infectious disease, a recently emerged transmissible cancer in Tasmanian devils (Sarcophilus harrisii) is virtually 100% fatal. Devil facial tumour disease (DFTD) has swept across nearly the entire species' range, resulting in localized declines exceeding 90% and an overall species decline of more than 80% in less than 20 years. Despite epidemiological models that predict extinction, populations in long-diseased sites persist. Here we report rare genomic evidence of a rapid, parallel evolutionary response to strong selection imposed by a wildlife disease. We identify two genomic regions that contain genes related to immune function or cancer risk in humans that exhibit concordant signatures of selection across three populations. DFTD spreads between hosts by suppressing and evading the immune system, and our results suggest that hosts are evolving immune-modulated resistance that could aid in species persistence in the face of this devastating disease.

Transmissible cancers in an evolutionary context.

Cancer is an evolutionary and ecological process in which complex interactions between tumour cells and their environment share many similarities with organismal evolution. Tumour cells with highest adaptive potential have a selective advantage over less fit cells. Naturally occurring transmissible cancers provide an ideal model system for investigating the evolutionary arms race between cancer cells and their surrounding micro-environment and macro-environment. However, the evolutionary landscapes in which contagious cancers reside have not been subjected to comprehensive investigation. Here, we provide a multifocal analysis of transmissible tumour progression and discuss the selection forces that shape it. We demonstrate that transmissible cancers adapt to both their micro-environment and macro-environment, and evolutionary theories applied to organisms are also relevant to these unique diseases. The three naturally occurring transmissible cancers, canine transmissible venereal tumour (CTVT) and Tasmanian devil facial tumour disease (DFTD) and the recently discovered clam leukaemia, exhibit different evolutionary phases: (i) CTVT, the oldest naturally occurring cell line is remarkably stable; (ii) DFTD exhibits the signs of stepwise cancer evolution; and (iii) clam leukaemia shows genetic instability. While all three contagious cancers carry the signature of ongoing and fairly recent adaptations to selective forces, CTVT appears to have reached an evolutionary stalemate with its host, while DFTD and the clam leukaemia appear to be still at a more dynamic phase of their evolution. Parallel investigation of contagious cancer genomes and transcriptomes and of their micro-environment and macro-environment could shed light on the selective forces shaping tumour development at different time points: during the progressive phase and at the endpoint. A greater understanding of transmissible cancers from an evolutionary ecology perspective will provide novel avenues for the prevention and treatment of both contagious and non-communicable cancers.