Peripheral complete blood cell count (CBC) and blood ratios, including neutrophil-to-lymphocyte ratio (NLR), neutrophil-to-red blood cell ratio (NRR), and platelet-to-lymphocyte ratio (PLR), have been used in the diagnosis and prognosis of several cancers; however, their relevance in canine splenic hemangiosarcoma (HSA) remains to be investigated. This study investigated whether CBC, NLR, NRR, and PLR could be diagnostic and prognostic biomarkers in dogs with splenic HSA. Analyzing medical records of 154 dogs undergoing splenectomy from 2018 to 2022, we found that dogs diagnosed with splenic HSA (n = 63) had significantly higher neutrophil counts (14.9 ± 9.7 vs. 12.6 ± 9.6; p < 0.001), increased NRR (3.7 ± 2.6 vs. 2.7 ± 3.7; p < 0.001), lower platelet counts (145 ± 111 vs. 270 ± 213; p < 0.001), and reduced PLR (139.4 ± 160.0 vs. 259.9 ± 278.0; p < 0.001) compared to dogs with other splenic lesions. This study also identified a higher risk of relapse and mortality associated with increased NRR (p < 0.001 and p = 0.012, respectively) and an inverse relationship with PLR (p = 0.015 and p = 0.033, respectively), whereas NLR showed no significant association. The multivariate survival analysis identified NRR as an independent prognostic factor for DFI [hazard ratio (1.837); 95% confidence interval (1.147–2.942); p = 0.011], while for OS, the association did not reach statistical significance [hazard ratio (1.510); 95% confidence interval (0.985–2.314); p = 0.059]. These findings highlight the potential of NRR and PLR as biomarkers for assessing diagnosis and prognosis in canine splenic HSA, advocating for further validation in the future.

Canine splenic hemangiosarcoma is a highly malignant vascular neoplasm and is among the most frequent and clinically relevant splenic tumors in dogs. Its biological behavior is characterized by rapid growth, marked invasiveness, and early metastatic dissemination, contributing to the poor prognosis commonly observed in affected animals. Clinically, splenic hemangiosarcoma often remains subclinical until acute presentation due to splenic rupture and hemoperitoneum, thereby substantially limiting opportunities for early diagnosis and timely therapeutic intervention. Despite advances in diagnostic imaging, surgical techniques, and the use of adjuvant chemotherapy, the impact of current therapeutic approaches on long-term survival remains limited. Splenectomy is primarily palliative for hemorrhage control, and adjuvant doxorubicin-based chemotherapy yields only modest improvements in median survival; alternative approaches (metronomic chemotherapy, immunotherapy, and targeted therapies) have not demonstrated consistent clinical benefit. This review summarizes the biological and pathophysiological features of canine splenic hemangiosarcoma, discusses the main clinical challenges associated with its diagnosis and staging, and critically reviews current therapeutic approaches and their limitations. By integrating biological behavior with clinical and therapeutic evidence, this article highlights the reasons why prognosis remains poor and underscores the need for more effective strategies to improve clinical outcomes in dogs with splenic hemangiosarcoma.