Cardiac hemangiosarcoma is ten times more common than other cardiac tumor types in dogs. Its clinical presentation is particularly concerning due to the high risk of acute mortality, primarily because these tumors often cause pericardial effusions that can lead to cardiac tamponade and compression of the heart chambers.
Without treatment, survival times are typically just 7 to 12 days. Surgical resection, when possible, has been associated with a median survival time of around 4 months. Studies comparing surgery alone versus surgery combined with chemotherapy report survival times of approximately 42 days without chemotherapy and 175 days with adjuvant chemotherapy. Monotherapy using doxorubicin alone has shown median survival times ranging from 116 to 140 days. Additionally, two smaller studies suggest that ionizing radiation targeting right auricular masses can significantly reduce the frequency of pericardial effusions, thereby prolonging survival.
This retrospective study aimed to evaluate and describe the outcomes of dogs with presumptive cardiac hemangiosarcoma treated with different radiation therapy protocols and modalities. Secondary objectives included assessing differences in survival between dogs that received chemotherapy after radiation therapy and those that did not, comparing single versus multiple radiation fractions, and evaluating outcomes based on treatment planning method—CT-guided versus manually calculated.
The study included 27 dogs with suspected cardiac hemangiosarcoma treated with various radiation protocols, the most common being a single 12 Gy fraction. Radiation-induced injury occurred more frequently in dogs treated with manually calculated, less conformal plans (66% versus 33%). However, the risk of missing microscopic disease with blocked fields likely outweighs the benefit of sparing organs at risk that have minimal impact on survival.
Dogs treated with 3D conformal radiation therapy lived longer than those treated with the more precise volumetric modulated arc therapy, suggesting that less conformal plans may inadvertently treat microscopic disease extensions, leading to improved survival. Nevertheless, the balance between tumor coverage and sparing healthy tissue remains an important consideration.
Adjuvant chemotherapy protocols varied widely in this study due to the extended retrospective inclusion period. Metastasis was the most common reason for euthanasia or death, underscoring the need for more effective systemic treatments. Recent evidence supports the use of vinblastine and propranolol after radiation therapy, with encouraging results in a small group of dogs without pre-existing pulmonary metastasis. Propranolol is gaining interest due to preclinical success in blocking beta-2 receptor signaling in neoplastic endothelial cells, an approach that has also shown promise in human cancers.
The median survival time between dogs with confirmed metastatic lesions and those without overt metastasis was similar (123 versus 142 days). Necropsies in this study and previous research found no evidence of metastatic spread to thoracic lymph nodes, though one case out of 51 showed sternal lymph node involvement on cytology.
Genomic studies of canine visceral hemangiosarcoma have revealed DNA copy number aberrations that are conserved within breed-specific subgroups, but no highly recurrent somatic alterations have been identified as definitive hallmarks of this cancer. Interestingly, significant differences were found when comparing Golden Retrievers with visceral hemangiosarcoma to other affected dogs.
The use of doxorubicin in cardiac hemangiosarcoma remains controversial when combined with radiation due to its known cardiotoxic effects at cumulative doses. This complicates the assessment of whether subsequent heart damage is caused by the tumor itself, radiation, or chemotherapy.
This study demonstrates that radiation therapy, across various protocols and intensities, can reduce pericardial effusion recurrence and decrease the need for emergency pericardiocentesis in dogs with suspected cardiac hemangiosarcoma. However, approximately 26% of dogs may experience re-effusion within the first month post-treatment, emphasizing the importance of close monitoring through clinical observation and serial cardiac ultrasound examinations every 1 to 2 weeks during this period.
While the data did not show a clear survival benefit from chemotherapy, metastatic disease was the primary cause of death in most cases. These findings support the role of radiation therapy in local disease control and highlight the need for further optimization of systemic therapies to address metastatic spread.
