Haemangiosarcoma is a malignancy arising from vascular endothelial cells or their bone marrow-derived precursors, and its biology makes it one of the most feared diagnoses in small animal practice. Tumours typically develop in the spleen, heart or skin, and with the exception of the cutaneous form they behave aggressively, metastasising early and producing vague, intermittent clinical signs that are easily mistaken for less serious conditions. Previous work has suggested the disease accounts for 40 to 64 percent of primary splenic disease and 46 percent of cardiac tumours in dogs. Because internal bleeding from a ruptured splenic mass is frequently the first visible sign, many affected dogs reach the clinic only in crisis. The new study’s finding that annual incidence and 12-month period prevalence were relatively similar, at 0.036 and 0.046 percent respectively, underscores how short survival typically is: dogs rarely live long enough with the disease for prevalence to accumulate far beyond incidence.

The sheer scale of the dataset allowed the researchers to do something earlier studies could not. Much of the existing literature on canine haemangiosarcoma comes from referral hospitals or insured populations, both of which skew toward owners who can afford extensive diagnostic workups. That selection bias limits how well findings generalise to the broader dog population. By contrast, VetCompass captures the everyday caseload of first-opinion practices, where most dogs actually receive care and where many diagnoses rest on clinical judgement rather than histopathology. The team ran two parallel nested case-control analyses: one including all clinically diagnosed cases regardless of laboratory confirmation, and a second restricted to the 273 cases supported by histopathological evidence. Comparing the two offered a way to test whether the broader clinical diagnoses still carry epidemiological signal, and reassuringly, the risk factor patterns proved broadly consistent across both models.

Breed emerged as the dominant risk factor, and the results contain genuine surprises. Ten breeds showed significantly increased odds of clinical haemangiosarcoma compared with crossbreeds, led by the Dogue de Bordeaux with an odds ratio of 9.56, followed by the Flat Coated Retriever at 8.33 and the German Shepherd Dog at 6.35. The Hungarian Vizsla also featured prominently at 5.49. In the histopathologically confirmed subset, the Flat Coated Retriever’s odds soared to 17.5 times those of crossbreeds, with the Vizsla, German Shepherd Dog, Beagle and Boxer also at elevated risk. Notably, the Flat Coated Retriever, Hungarian Vizsla and Beagle had not previously been flagged at this level of confidence in large-scale studies, a gap the authors attribute to the statistical power afforded by their enormous sample. Six breeds, including the Jack Russell Terrier and Yorkshire Terrier, showed reduced odds, offering a counterpoint that may help clinicians weigh risk in small breeds presenting with splenic disease.

The breed findings carry weight beyond the consulting room because they point toward genetic predisposition. When the researchers replaced breed with derived variables in their models, dogs in the lowest bodyweight category under 7.5 kilograms had markedly reduced odds, while risk climbed steadily with size, reaching an odds ratio of 4.42 for dogs weighing 37.5 kilograms or more in the clinical model and 5.17 in the histopathological model. Genotype-based breed grouping told a similar story, with the GG1 group, which includes the German Shepherd Dog, Portuguese Water Dog and Doberman Pinscher, showing roughly threefold increased odds of clinical diagnosis. The authors caution, however, that the prominence of German Shepherd Dogs within these groupings may skew the results, and assuming every breed in a high-risk group shares the risk would be an ecological fallacy. Still, the consistent signal across Kennel Club pastoral and working groups and ancestral mountain-type breeds strengthens the case that inherited factors shape susceptibility, opening a potential route to risk reduction through altered breeding practices and outcrossing in high-risk lines.

Age produced a pattern that was strikingly non-linear. Compared with dogs aged seven to under nine years, those aged 11 to under 13 had the highest odds of clinical diagnosis at 2.83, while dogs aged five to under seven had only 0.22 times the odds. Yet in the histopathological subset, peak odds shifted younger, to the nine-to-eleven-year bracket, and univariable comparisons showed that the probability of obtaining histopathological confirmation actually declined with age. The researchers suggest this reflects owner decision-making rather than tumour biology: older dogs may be less likely to undergo the surgery needed to obtain tissue, whether because of cost, anaesthetic risk or insurance status. There is also a worrying possibility that symptoms in very elderly dogs are attributed to old age, delaying veterinary visits and allowing the disease to kill before it is ever diagnosed, a scenario the authors urge veterinarians to counter by helping owners of senior dogs recognise warning signs.

Reproductive status, socioeconomic context and geography all left fingerprints on the data, albeit more subtly. Neutered males showed increased odds of clinical diagnosis compared with entire females at 1.49, with neutered females at 1.28, a pattern directionally consistent with an Italian register-based study of visceral haemangiosarcoma, though the effect was smaller here and reproductive status dropped out of the histopathological model entirely. Dogs attending clinics in the least deprived areas of the UK had 1.66 times the odds of clinical diagnosis compared with those in the most deprived areas, an association the authors interpret cautiously, noting it may reflect differences in insurance uptake and owners’ willingness to pursue definitive diagnostics rather than true differences in disease occurrence. Intriguingly, dogs attending clinics in mixed urban-rural areas had reduced odds of 0.71 compared with urban clinics, a novel finding given that previous investigations of environment and pollution exposure had been inconclusive.

The study is not without limitations, and the authors are candid about them. Because the data were collected for clinical rather than research purposes, some cases may have gone unrecorded, and conversely some clinically diagnosed cases lacking histopathological confirmation may have been false positives, particularly given the risk of confirmation bias when veterinarians encounter breeds already known to be predisposed. Roughly two-thirds of incident clinical cases were diagnosed without laboratory confirmation, which is simply the reality of primary care where invasive or costly diagnostics are often inappropriate for dogs with advanced disease. The histopathological analysis, with only 273 cases, is likely underpowered for less common breeds, and the restriction of risk factor modelling to dogs aged five and older limits generalisability to younger animals. None of these caveats, however, undermines the central value of the work: a population-level baseline that referral-based studies structurally cannot provide.

For practicing veterinarians and dog owners, the practical payoff is earlier suspicion. Visceral haemangiosarcoma presents with signs so vague and intermittent that any tool sharpening clinical triage matters, and knowing that a middle-aged Flat Coated Retriever, German Shepherd Dog or large-bodied crossbreed faces several-fold elevated odds should prompt a lower threshold for imaging and targeted workup. For researchers, the newly identified high-risk breeds offer fresh leads for the genetic studies needed to unravel a disease whose pathogenesis remains poorly understood despite decades of investigation. And for breeders, the evidence that predisposition clusters within breed lines and genotype groups supports serious consideration of outcrossing strategies in the most affected breeds. With 2.25 million dogs represented and the full dataset made openly available, this study sets a new reference point for canine cancer epidemiology in the UK and a template for how primary-care data can illuminate diseases that are all too often diagnosed only in their final, fatal act.

Subject of Research: Epidemiology and risk factors for canine haemangiosarcoma in UK primary veterinary care

Article Title: Epidemiology of haemangiosarcoma diagnosed in dogs under primary veterinary care in the United Kingdom: Frequency and risk factors

Article References: Epidemiology of haemangiosarcoma diagnosed in dogs under primary veterinary care in the United Kingdom: Frequency and risk factors. (n.d.). https://doi.org/10.1186/s44356-025-00041-4

Image Credits: AI Generated

DOI: 10.1186/s44356-025-00041-4

Keywords: haemangiosarcoma, dogs, veterinary oncology, VetCompass, epidemiology, breed risk, cancer, risk factors, UK, primary veterinary care, genetics, splenic tumours