Largest Study of Its Kind Reveals How Australian Dogs Fare Against Lymphoma

Canine lymphoma is one of the most common cancers diagnosed in dogs worldwide, yet the clinical picture in Australia has remained remarkably poorly documented. Now, in the largest study of its kind conducted in the country, researchers at the University of Sydney and the University of Melbourne have analysed 1366 confirmed cases of lymphoma in Australian dogs, drawing on more than two decades of records from two referral hospitals separated by 701 kilometres. The findings, published in the journal Veterinary Oncology, offer the most detailed portrait to date of how the disease presents, how it responds to treatment, and which factors shape survival in a geographically isolated canine population that has long been absent from the global evidence base.

The retrospective cohort study searched electronic patient databases for all dogs diagnosed with lymphoma or lymphosarcoma between 1 January 2000 and 31 December 2021, with case status reviewed in May 2023. To be included, dogs required a diagnosis confirmed by cytology or histology and consistent clinical findings, reviewed by a board-certified veterinary oncologist. Dogs that had received prior chemotherapy, radiation or immunotherapy were excluded, although those previously treated with glucocorticoids were retained. The final cohort of 1366 dogs represented 1.6 percent of the hospital population over the study period, with 451 cases from the university teaching hospital and 915 from a private referral centre. More than 105 breeds were represented, alongside crossbred dogs.

The demographics of the cohort revealed a disease of middle-aged and older dogs. Ages ranged from just over two months to 17.7 years, with a median of 8.5 years, and median body weight of 23.2 kilograms. Neutered animals dominated the population, accounting for 84.5 percent of cases. The overwhelming majority of dogs, 72 percent, presented with multicentric or nodal disease, and 93.7 percent of those were at stage III or higher at diagnosis, underscoring how frequently lymphoma is advanced by the time it is recognised. Cutaneous lymphoma was the next most common form at 10.2 percent, followed by gastrointestinal disease at 6.1 percent and mediastinal disease at 2.9 percent. Where immunophenotyping was performed, B-cell tumours slightly outnumbered T-cell tumours, 53 percent to 45 percent.

The researchers also mapped the interconnections between laboratory abnormalities and clinical presentation, uncovering a web of statistically significant associations. Anaemia was more frequent in dogs with advanced stage, gastrointestinal disease, substage b, thrombocytopenia, hypoalbuminaemia and reduced appetite. Hypercalcaemia clustered with mediastinal disease, T-cell immunophenotype and advanced stages. Reduced appetite, recorded consistently in the medical records independently of substage, was associated with nearly every adverse marker, including anaemia, thrombocytopenia, hypercalcaemia and hypoalbuminaemia. These patterns suggest that a constellation of systemic derangements travels together in canine lymphoma, and that appetite may serve as a simple bedside indicator of disease burden.

Treatment patterns reflected the realities of veterinary oncology practice. The most common initial approach was a CHOP-based combination protocol, built on cyclophosphamide, doxorubicin, vincristine and prednisolone, used in 480 dogs, with a further 62 dogs receiving T-cell specific regimens. Other dogs received single-agent doxorubicin, mitoxantrone or lomustine, glucocorticoids alone, surgery, or a variety of other combinations. Notably, 355 dogs, or 26 percent, received no recorded treatment, and 26 were euthanised at diagnosis, figures that highlight the difficult decisions owners face when confronted with an aggressive cancer and the cost and commitment that intensive chemotherapy demands.

The core outcome analysis focused on the 542 dogs treated with CHOP-based protocols, of which 532 had sufficient pre-treatment data. The overall response rate was 87.5 percent, with 67.4 percent achieving complete remission and 20 percent partial remission. The median progression-free survival time was 200 days, and the median overall survival time was 252 days, with one-year survival estimates of roughly 25.6 percent for progression-free survival and 37.2 percent for overall survival. These figures place Australian dogs squarely within, though at the lower end of, the ranges reported from large European and North American studies, a reassuring finding given concerns that quarantine-driven genetic isolation, different breed demographics and environmental factors might produce divergent outcomes.

Perhaps the most striking result was the identification of the treating hospital itself as an independent prognostic factor for both progression-free and overall survival, despite the two centres sharing similar climates, breed profiles and referral-based management. The researchers could not identify an obvious difference in clinical management, other than less frequent steroid use at one hospital, and speculate that unmeasured differences in case mix or unidentified biases may be responsible. The finding carries a practical message for the field: when multi-centre veterinary studies pool cases to boost numbers, the treating clinic should be treated as a variable in the analysis, something rarely done in veterinary oncology to date.

Two further novel or rarely reported prognostic variables emerged. Reduced appetite at diagnosis independently predicted shorter progression-free and overall survival, a factor that has been investigated in only two prior studies and confirmed in just one, possibly because appetite is usually folded into substage rather than analysed on its own. And in a subset analysis restricted to breeds with ten or more cases, breed significantly influenced overall survival: compared with crossbred dogs, boxers, golden retrievers and Labrador retrievers had significantly shorter survival, with hazard ratios of 1.98, 2.09 and 3.02 respectively. Intriguingly, all three breeds are also recognised as being at elevated risk of developing lymphoma in Australia, hinting that the genetic factors which predispose certain breeds to the disease may also shape how their tumours respond to treatment.

The study also weighed in on a long-running controversy: the role of glucocorticoids within combination chemotherapy. Prior glucocorticoid exposure before chemotherapy showed no significant effect on outcome in any group, allowing clinicians some reassurance that short-term palliative steroid use while awaiting chemotherapy is unlikely to compromise later results. However, dogs whose CHOP protocols included prednisolone had significantly shorter progression-free and overall survival and lower remission rates than those whose protocols omitted it, even after multivariate adjustment. Because steroid inclusion was at clinician discretion, bias towards treating sicker dogs with steroids cannot be excluded, and the authors caution that this finding requires independent confirmation before practice changes.

The consistent prognostic anchor across nearly all analyses was response to initial treatment, confirming its status as the most reliable predictor of survival in canine lymphoma, yet one that cannot be known before therapy begins. The authors argue that identifying an accessible, cost-effective predictor of response at diagnosis remains one of the field’s most pressing needs, and would transform the conversations veterinarians have with owners contemplating treatment. For Australian dogs and their veterinarians, the broader message is one of connection: outcomes in this isolated population mirror those reported internationally, meaning that evidence from global studies can be applied to Australian patients, and Australian data, now substantially richer, can inform the world.

The scale of the new study deserves emphasis in context. Large veterinary lymphoma cohorts exceeding 200 treatment-naïve dogs are rare in the global literature, and the Australian dataset of 1366 cases, accumulated over 22 years, now ranks among the most extensive regional collections published anywhere. This matters because most of what veterinarians know about canine lymphoma prognosis derives from North American and European institutions, where breed distributions, referral patterns and owner attitudes toward chemotherapy may differ substantially from those in an island continent with strict quarantine controls shaping its dog population for generations.

The methodological grounding of the work also strengthens its conclusions. Survival endpoints were calculated in alignment with the Veterinary Comparative Oncology Group consensus criteria, the standardised response framework adopted across veterinary oncology since 2010, with earlier records retrospectively mapped onto those definitions. Progression-free and overall survival were measured from the commencement of treatment, and dogs still in remission at last examination were right censored rather than counted as failures. Overall survival was chosen over lymphoma-specific survival because, even when another cause of death was recorded, the authors could not exclude lymphoma as a contributing factor, a conservative decision that avoids inflating favourable outcomes.

The definition of a modified CHOP protocol also clarifies how real-world practice diverges from textbook regimens. Substituting mitoxantrone for doxorubicin in dogs with cardiac disease, adding agents such as L-asparaginase, or extending protocols to 19 or 25 weeks all qualified, reflecting the clinical judgement that shapes individualised care. By analysing these dogs alongside standard CHOP recipients, the study captures the heterogeneity of referral practice that pure prospective trials often exclude, at the cost of some protocol standardisation.

Several limitations temper interpretation. As a retrospective cohort, the study depended on owner willingness and financial capacity to pursue complete staging, meaning some recorded stages represent minimum estimates, particularly for dogs clinically at stage III. Immunophenotyping was not performed in every case, and the glucocorticoid findings rest on clinician discretion rather than randomisation, leaving residual confounding by case severity an open possibility. The hospital effect, while statistically robust, remains biologically unexplained.

For practicing veterinarians, the practical takeaways are concrete. Appetite at diagnosis, already routinely recorded, merits attention as an independent prognostic marker rather than a mere component of substage. Multi-institutional studies should treat the treating hospital as an analytical variable. And the finding that Australian outcomes sit within international ranges, albeit at the lower end, provides a defensible evidence base for applying global trial results to Australian patients while encouraging local participation in future multi-centre studies.

Subject of Research: Presentation, treatment outcomes and prognostic factors for canine lymphoma in Australian dogs

Article Title: A retrospective study on the presentation and outcomes for Australian dogs with lymphoma: 1366 cases

Article References: Bennett, P., Williamson, P., & Taylor, R. (2026). A retrospective study on the presentation and outcomes for Australian dogs with lymphoma: 1366 cases. Veterinary Oncology, 3(1), Article 19. https://doi.org/10.1186/s44356-026-00070-7

Image Credits: AI Generated

DOI: 10.1186/s44356-026-00070-7

Keywords: canine lymphoma, dogs, chemotherapy, CHOP protocol, prognostic factors, veterinary oncology, survival, glucocorticoids, breed risk, Australia, B-cell lymphoma, T-cell lymphoma