Study highlights radiation outcomes in canine non-visceral HSA
Bottom line
A new retrospective study in Frontiers in Veterinary Science suggests hypofractionated radiation therapy may offer meaningful local control for dogs with subcutaneous and intramuscular hemangiosarcoma when used in a multimodal setting. Investigators at Washington State University reviewed 53 dogs treated with either 24 Gy in three 8-Gy fractions or 30 Gy in five 6-Gy fractions, usually alongside chemotherapy and sometimes surgery. Among 30 evaluable dogs, the objective response rate to radiation was 93%, including 37% complete responses and 56% partial responses. Median overall survival for the full cohort was 306 days, and anemia emerged as the only independent predictor of shorter survival in multivariable analysis. The paper also found dogs that underwent surgery before radiation had markedly longer median survival than those that did not, although surgery did not remain independently significant after adjustment. Radiation-related adverse events were generally mild. (frontiersin.org)
Why it matters: For veterinary professionals, the study adds contemporary evidence for using radiation in a disease setting where local control can be difficult and published data have been limited. Current AAHA oncology guidance notes that radiation is a localized therapy best suited to solitary or regionally confined disease, and that outcomes are strongest when tumors are reduced to microscopic disease before treatment. That framework fits this study’s signal that surgery plus radiation may be most useful when feasible, while also underscoring that anemia and metastatic status can help inform prognosis and client conversations with pet parents. The findings also update older literature showing outcome differences between subcutaneous and intramuscular hemangiosarcoma and reinforce that systemic chemotherapy alone has not consistently changed survival in these non-visceral cases. (aaha.org)
What to watch: Prospective, multi-institutional studies will be needed to clarify which dogs benefit most from surgery, radiation timing, and concurrent doxorubicin, especially in patients with gross disease at the start of treatment. (frontiersin.org)
Key facts
- Study type
- Retrospective study
- Journal
- Frontiers in Veterinary Science
- Institution
- Washington State University
- Sample size
- 53 dogs
- Disease
- Subcutaneous and intramuscular hemangiosarcoma
- Radiation protocols
- 24 Gy in three 8-Gy fractions, or 30 Gy in five 6-Gy fractions
- Concurrent treatment
- Most dogs also received chemotherapy, usually doxorubicin
- Objective response rate
- 93% among 30 evaluable dogs
- Median overall survival
- 306 days
Hypofractionated radiation therapy may be gaining a clearer role in the management of canine subcutaneous and intramuscular hemangiosarcoma. In a newly published retrospective study in Frontiers in Veterinary Science, researchers reported high response rates, generally mild toxicity, and potentially durable local control in 53 dogs treated with short-course radiation, usually as part of multimodal care that also included chemotherapy and, in some cases, surgery. (frontiersin.org)
That matters because the role of radiation in non-visceral hemangiosarcoma has remained somewhat unsettled. Surgery has long been the primary local treatment, but these tumors can be infiltrative, margins are often incomplete, and recurrence is a persistent concern. AAHA’s 2026 oncology guidelines describe radiation as a localized modality that is particularly valuable for solitary or regionally isolated disease, with the best long-term control typically achieved when tumor burden is reduced to microscopic disease before treatment. (aaha.org)
In the new study, Washington State University investigators evaluated dogs treated with one of two hypofractionated protocols: 24 Gy in three 8-Gy fractions delivered on days 0, 7, and 21, or 30 Gy in five 6-Gy fractions delivered every other day. Of the 53 dogs included, 27 had subcutaneous hemangiosarcoma and 26 had intramuscular disease; 35 dogs, or 66%, had macroscopic disease at the time of radiation. Most dogs, 47 of 53, also received chemotherapy, and doxorubicin was the dominant agent. Among 30 evaluable dogs, the objective response rate was 93%. Local progression or recurrence occurred in 11 of 36 dogs after a median of 128 days, mostly in dogs with macroscopic disease, while median time to progression was not reached. Median overall survival for the cohort was 306 days. (frontiersin.org)
The prognostic findings are likely to be the most clinically useful takeaway. On univariable analysis, anemia, absence of surgery, macroscopic disease at radiation, metastasis, and tumor size greater than 6 cm were associated with shorter survival. In multivariable analysis, anemia remained independently associated with a higher risk of death. Dogs that underwent surgery before radiation had a much longer median survival, 2,059 days versus 287 days, though that association did not stay independently significant after adjustment. The authors also reported that chemotherapy was not associated with survival in this cohort. (frontiersin.org)
The study builds on earlier work from the same disease space. A 2008 report of 21 dogs treated with adequate local control and adjuvant doxorubicin found more favorable outcomes in subcutaneous than intramuscular tumors, while a 2011 prognostic analysis identified factors such as anemia, stage, and extent of disease as important predictors of outcome in dogs with subcutaneous or intramuscular hemangiosarcoma. Rebelo’s earlier Washington State University thesis, completed in 2024 and apparently forming the basis for the new paper, similarly pointed to anemia, metastasis, lack of surgery, and larger tumor size as negative prognostic indicators. (pubmed.ncbi.nlm.nih.gov)
Industry and guideline context also supports the paper’s practical relevance. AAHA’s current oncology guidance lists subcutaneous hemangiosarcoma among tumors for which radiation may be used when lesions are large, invasive, or difficult to resect, while broader veterinary oncology consensus documents recommend adjuvant radiation for incompletely excised soft tissue mesenchymal tumors to improve local control. Taken together, the new data don’t establish a new standard of care, but they do strengthen the case for discussing radiation earlier, especially when complete excision is unlikely or when gross disease remains. (aaha.org)
Why it matters: For practicing veterinarians and oncologists, this study offers a more concrete framework for case selection and prognosis. The strongest signal is that local therapy still matters in a metastatic-prone cancer: dogs with smaller tumors, no anemia, no metastasis, and the ability to undergo surgery before radiation appear to have the best chance for prolonged control. At the same time, the high response rate in dogs with measurable disease suggests hypofractionated radiation may also be useful when the goal is cytoreduction or palliation, particularly if a shorter protocol is needed for patient tolerance, logistics, or pet parent decision-making. (frontiersin.org)
What to watch: The next step is better prospective evidence, ideally multi-institutional, to separate the effects of surgery, radiation schedule, chemotherapy, and disease burden at treatment start. Clinicians will also want more clarity on whether concurrent doxorubicin adds benefit, and whether anemia is simply a marker of more advanced disease or a modifiable factor that should change treatment planning and counseling. (frontiersin.org)