Hemangiosarcoma

Hemangiosarcoma (HSA) is a highly malignant mesenchymal neoplasm arising from vascular endothelial cells. It is characterized by aggressive local invasion, early and widespread hematogenous metastasis, and a poor prognosis. The tumor can arise in any vascularized tissue, but in dogs, the most common primary sites are the spleen, right atrium/auricle, liver, and skin/subcutis. In cats, HSA is less common but typically involves the spleen, liver, or skin. The disease is often clinically silent until rupture of the tumor leads to acute hemorrhage, collapse, or sudden death. Histologically, HSA is composed of pleomorphic spindle cells forming irregular vascular channels filled with blood. The tumor is highly vascular and friable, predisposing to spontaneous bleeding. Staging is crucial for prognosis and treatment planning, with the most widely used system being the World Health Organization (WHO) clinical staging for splenic HSA: Stage I (confined to spleen, no rupture), Stage II (ruptured or regional lymph node involvement), Stage III (distant metastasis).

The exact etiology of hemangiosarcoma is unknown, but several factors have been implicated. Chronic ultraviolet (UV) light exposure is a well-established risk factor for cutaneous HSA in dogs, particularly in lightly pigmented, thinly haired skin areas (e.g., ventral abdomen, prepuce, inguinal region). In visceral HSA, no definitive cause has been identified, but genetic predisposition is strongly suspected. Specific genetic mutations and chromosomal aberrations have been identified in canine HSA, including mutations in the TP53 tumor suppressor gene, overexpression of vascular endothelial growth factor (VEGF) and its receptors (VEGFR-1, VEGFR-2), and activation of the PI3K/Akt/mTOR signaling pathway. Environmental toxins, such as exposure to vinyl chloride, have been linked to hepatic angiosarcoma in humans, but similar associations are not well-documented in dogs. Ionizing radiation has been reported to induce HSA in experimental settings. In cats, feline leukemia virus (FeLV) infection has been associated with an increased risk of developing HSA, particularly in younger cats, although the exact oncogenic mechanism is unclear. Chronic inflammation and trauma have been suggested as potential triggers for cutaneous HSA, but evidence is limited.

Hemangiosarcoma is primarily a disease of dogs, accounting for approximately 5-7% of all canine neoplasms. It is the most common primary cardiac tumor in dogs and the most common splenic malignancy. The incidence is higher in middle-aged to older dogs, with a median age of 9-11 years. Certain breeds are overrepresented, including Golden Retrievers, Labrador Retrievers, German Shepherd Dogs, Boxers, and Bernese Mountain Dogs. There is a slight male predominance in some studies. In cats, HSA is rare, accounting for less than 2% of feline neoplasms, with a median age of 10-12 years. No strong breed predilection is noted in cats, but Siamese and Domestic Shorthair cats may be at higher risk. Cutaneous HSA is more common in dogs with short, white, or lightly pigmented coats, such as Whippets, Italian Greyhounds, and Pit Bull Terriers, due to UV exposure. Visceral HSA has no geographic predilection, but cutaneous HSA is more prevalent in sunny climates. The incidence of splenic HSA in dogs is estimated at 0.3-0.5% of all canine necropsies.

Hemangiosarcoma arises from endothelial cells, which normally line blood vessels. Malignant transformation leads to uncontrolled proliferation of these cells, forming irregular, blood-filled vascular channels. The tumor is highly invasive and can rapidly infiltrate surrounding tissues. Key pathophysiological mechanisms include: 1) Angiogenesis: The tumor secretes VEGF and other pro-angiogenic factors, promoting the formation of new blood vessels to supply the growing mass. 2) Coagulopathy: The abnormal vascular channels and endothelial dysfunction lead to platelet activation, consumption of clotting factors, and microangiopathic hemolytic anemia. Disseminated intravascular coagulation (DIC) is a common complication, especially in advanced stages. 3) Hemorrhage: The tumor is fragile and prone to rupture, leading to acute blood loss into the abdominal or thoracic cavity, resulting in hypovolemic shock and anemia. 4) Metastasis: Hematogenous spread is the primary route, with early metastasis to the liver, omentum, lungs, and brain. The right atrium is a common site for primary cardiac HSA, which can cause cardiac tamponade and arrhythmias. 5) Paraneoplastic syndromes: HSA can produce erythropoietin, leading to erythrocytosis, and may cause hypoglycemia due to insulin-like growth factor secretion. 6) Systemic inflammation: Tumor necrosis and hemorrhage can trigger a systemic inflammatory response, contributing to cachexia and organ dysfunction.

Predisposing factors for hemangiosarcoma include: 1) Breed: Large and giant breeds, particularly Golden Retrievers, Labrador Retrievers, German Shepherds, Boxers, and Bernese Mountain Dogs, have a higher risk. 2) Age: Middle-aged to older dogs (median 9-11 years) are most commonly affected. 3) Sex: Some studies suggest a slight male predisposition. 4) UV light exposure: For cutaneous HSA, chronic sun exposure in lightly pigmented, thinly haired skin areas is a major risk factor. 5) Genetic mutations: Inherited mutations in TP53 and other oncogenes may predispose certain breeds. 6) Environmental carcinogens: Exposure to chemicals such as vinyl chloride, thorium dioxide, and arsenic has been linked to angiosarcoma in humans and may be relevant in animals. 7) Feline leukemia virus (FeLV) infection: In cats, FeLV infection increases the risk of HSA. 8) Immunosuppression: Chronic immunosuppression, whether due to disease or medication, may increase susceptibility. 9) Prior radiation therapy: Radiation exposure can induce HSA in rare cases.

Clinical signs of hemangiosarcoma depend on the primary site and the presence of metastasis. In splenic HSA, the most common presentation is acute collapse due to tumor rupture and hemoabdomen. Owners may report a history of lethargy, weakness, pale mucous membranes, and abdominal distension. Some dogs may have chronic signs such as intermittent anorexia, weight loss, and exercise intolerance. Cardiac HSA often presents with signs of right-sided heart failure, including ascites, jugular venous distension, and muffled heart sounds due to pericardial effusion. Arrhythmias may cause syncope or sudden death. Cutaneous HSA appears as a rapidly growing, often ulcerated, dark red to black mass on the skin. It may bleed easily and can be mistaken for a hematoma. Hepatic HSA may cause hepatomegaly, icterus, and abdominal pain. Metastatic disease can lead to respiratory signs (dyspnea, cough) if pulmonary metastasis occurs, or neurological signs if brain metastasis is present. Paraneoplastic erythrocytosis may cause polyuria, polydipsia, and ruddy mucous membranes. In cats, signs are similar but may be more vague, including lethargy, anorexia, and weight loss.

Differential diagnoses for hemangiosarcoma include: 1) Splenic hematoma: A benign, encapsulated blood-filled mass that can also rupture and cause hemoabdomen. Differentiation requires histopathology; hematomas have a well-organized fibrin capsule and no malignant endothelial cells. 2) Splenic nodular hyperplasia: Benign proliferation of splenic tissue, often multiple nodules, may be indistinguishable on imaging but lacks the aggressive features of HSA. 3) Other splenic neoplasms: Lymphoma, histiocytic sarcoma, and metastatic carcinoma can present similarly. Histopathology is definitive. 4) Cardiac tumors: Other cardiac neoplasms such as chemodectoma, ectopic thyroid carcinoma, or mesothelioma can cause pericardial effusion. Echocardiography and cytology of pericardial fluid may help, but histopathology is needed. 5) Hepatic neoplasms: Hepatocellular carcinoma, biliary carcinoma, or metastatic tumors can cause hepatomegaly and abdominal effusion. 6) Peritoneal carcinomatosis: Diffuse abdominal neoplasia can cause effusion and mass lesions. 7) Coagulopathies: Conditions causing spontaneous bleeding, such as rodenticide toxicity, immune-mediated thrombocytopenia, or DIC, can mimic acute hemoabdomen. 8) Trauma: Blunt abdominal trauma can cause splenic rupture and hemoabdomen. 9) Abscess or granuloma: Infectious or inflammatory masses can mimic tumors on imaging. 10) Skin masses: For cutaneous HSA, differentials include hemangioma, mast cell tumor, melanoma, and other soft tissue sarcomas.

The diagnostic approach to hemangiosarcoma should be systematic: 1) History and physical examination: Identify signalment, clinical signs, and any palpable masses. 2) Complete blood count (CBC), serum biochemistry, and urinalysis: Look for anemia, thrombocytopenia, leukocytosis, elevated liver enzymes, and evidence of DIC. 3) Coagulation profile: Prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen, and D-dimer to assess for DIC. 4) Thoracic radiographs: Three-view (right lateral, left lateral, ventrodorsal) to detect pulmonary metastasis. 5) Abdominal ultrasound: Evaluate the spleen, liver, and other abdominal organs for masses, effusion, and metastasis. 6) Echocardiography: If cardiac involvement is suspected, especially in breeds at risk, to identify right atrial masses and pericardial effusion. 7) Fine-needle aspiration (FNA) of masses: Cytology may be suggestive but is often nondiagnostic due to blood contamination; it can help rule out other neoplasms. 8) Abdominocentesis: If hemoabdomen is present, collect fluid for analysis; the presence of non-clotting blood with a PCV similar to peripheral blood is supportive. 9) Surgical biopsy: Definitive diagnosis requires histopathology of the mass, typically obtained via splenectomy or mass excision. 10) Staging: After diagnosis, stage the disease based on WHO criteria (I, II, III) to guide treatment and prognosis. 11) Advanced imaging: CT or MRI may be used for surgical planning and to detect occult metastasis.

Laboratory findings in hemangiosarcoma are variable but often include: 1) Hematology: Anemia (regenerative or non-regenerative depending on chronicity), thrombocytopenia (due to consumption or DIC), leukocytosis with neutrophilia and left shift. Schistocytes and acanthocytes may be seen on blood smear, indicating microangiopathic hemolysis. 2) Serum biochemistry: Elevated liver enzymes (ALT, AST, ALP) if hepatic involvement; hypoglycemia may occur due to paraneoplastic insulin-like growth factor secretion; hyperbilirubinemia if biliary obstruction. 3) Coagulation profile: Prolonged PT and aPTT, decreased fibrinogen, elevated D-dimer, and thrombocytopenia are consistent with DIC. 4) Urinalysis: May show proteinuria or hematuria if renal metastasis. 5) Cardiac biomarkers: Elevated cardiac troponin I (cTnI) may be seen with cardiac HSA. 6) Erythrocytosis: In rare cases, erythropoietin production by the tumor leads to increased PCV. 7) Blood gas analysis: May reveal metabolic acidosis due to hypovolemic shock. 8) Cytology of effusion: Hemoabdomen fluid is typically a non-clotting bloody effusion with a PCV >10% and often >25%. Cytology may show reactive mesothelial cells but rarely neoplastic cells.

Imaging findings in hemangiosarcoma: 1) Thoracic radiographs: May show pulmonary metastasis as multiple soft tissue nodules, pleural effusion, or an enlarged cardiac silhouette if pericardial effusion is present. 2) Abdominal radiographs: May reveal splenomegaly, a soft tissue mass effect, or loss of abdominal detail due to effusion. 3) Abdominal ultrasound: Splenic HSA typically appears as a complex, mixed echogenic mass with cavitations and areas of necrosis. Hepatic masses may be hypoechoic or target-like. Free abdominal fluid is often anechoic. Doppler ultrasound may show turbulent blood flow within the mass. 4) Echocardiography: A right atrial or auricular mass is often seen as a hyperechoic or mixed echogenic mass attached to the atrial wall, with pericardial effusion. 5) CT: Provides detailed assessment of the primary mass, vascular invasion, and metastasis. CT angiography can help identify the vascular nature of the tumor. 6) MRI: Useful for brain metastasis evaluation. 7) Fluoroscopy: Not typically used for HSA diagnosis.

Cytology: Fine-needle aspiration of HSA often yields blood and few intact cells, making cytologic diagnosis challenging. When cells are obtained, they may be spindle-shaped with anisocytosis, anisokaryosis, and prominent nucleoli. However, cytology is more useful for ruling out other neoplasms (e.g., lymphoma, mast cell tumor). Histopathology: Definitive diagnosis requires biopsy. Grossly, HSA is a dark red to black, friable mass with areas of hemorrhage and necrosis. Microscopically, it is composed of pleomorphic spindle cells forming irregular, anastomosing vascular channels lined by atypical endothelial cells. Mitotic figures are frequent. Immunohistochemistry (IHC) can confirm endothelial origin with positive staining for factor VIII-related antigen, CD31, and vimentin. Special stains such as Masson's trichrome may help differentiate from other sarcomas. Histologic grading (based on mitotic count, necrosis, and differentiation) may have prognostic value, but the clinical stage is more important.

Treatment of hemangiosarcoma is multimodal and depends on the stage and location. 1) Emergency stabilization: For acute hemoabdomen, aggressive fluid resuscitation with crystalloids and colloids, blood transfusion (packed red blood cells or whole blood), and oxygen supplementation are critical. 2) Surgery: Splenectomy is the primary treatment for splenic HSA. Complete excision of the mass with clean margins is ideal. For cardiac HSA, surgical resection is often not feasible due to location, but subtotal pericardectomy may relieve tamponade. Cutaneous HSA is treated with wide surgical excision (3 cm margins) and histologic evaluation of margins. 3) Chemotherapy: Adjuvant chemotherapy is recommended to delay metastasis and improve survival. The most effective protocol is doxorubicin-based. Common protocols include: Doxorubicin (30 mg/m² IV every 3 weeks) alone or in combination with cyclophosphamide (50-75 mg/m² PO on days 3-6) or vincristine (0.5-0.7 mg/m² IV on day 8) (VAC protocol). Metronomic chemotherapy with cyclophosphamide (10-15 mg/m² PO daily) and piroxicam (0.3 mg/kg PO every 24 hours) has also been used. 4) Radiation therapy: For cutaneous HSA, radiation may be used postoperatively if margins are incomplete. 5) Supportive care: Pain management with opioids (e.g., buprenorphine 0.01-0.03 mg/kg IV/IM q8-12h) or NSAIDs (e.g., carprofen 2.2 mg/kg PO q12h) after surgery. Gastrointestinal protectants (e.g., omeprazole 1 mg/kg PO q24h) if on NSAIDs. 6) Management of DIC: Fresh frozen plasma (10-15 ml/kg IV) and heparin (e.g., 200-300 IU/kg SC q8h) may be considered. 7) Alternative therapies: Tyrosine kinase inhibitors (e.g., toceranib 2.75 mg/kg PO every other day) have shown some activity in HSA. 8) Nutritional support: High-quality protein diet, omega-3 fatty acids (e.g., EPA/DHA 40 mg/kg/day) may help with cachexia.

The prognosis for hemangiosarcoma is generally poor to grave. For splenic HSA, median survival time (MST) with surgery alone is approximately 1-3 months. With surgery and adjuvant doxorubicin-based chemotherapy, MST increases to 5-8 months. One-year survival rates are less than 10%. Stage is the most important prognostic factor: Stage I (no rupture) has a better prognosis than Stage II (rupture) or Stage III (metastasis). Cardiac HSA has a very poor prognosis, with MST of 3-6 months even with treatment. Cutaneous HSA has a better prognosis if completely excised, with MST of 1-2 years, but metastasis can still occur. Negative prognostic factors include: presence of metastasis, tumor rupture, high mitotic index, and elevated cTnI. Positive prognostic factors include: complete surgical excision, stage I disease, and cutaneous location.

Follow-up for hemangiosarcoma should be intensive due to high risk of metastasis. 1) Recheck examinations: Every 1-2 months for the first 6 months, then every 3 months for the next 6 months, then every 6 months thereafter. 2) Imaging: Thoracic radiographs (3-view) and abdominal ultrasound should be repeated every 2-3 months to detect metastasis. 3) Laboratory monitoring: CBC, serum biochemistry, and coagulation profile (PT/aPTT, D-dimer) should be checked before each chemotherapy treatment and if clinical signs suggest DIC. 4) Echocardiography: If cardiac HSA, repeat echocardiography every 2-3 months to assess for pericardial effusion or tumor growth. 5) Chemotherapy monitoring: Serial echocardiography (for doxorubicin cardiotoxicity) and urinalysis (for cyclophosphamide-induced cystitis) are recommended. 6) Quality of life assessment: Use validated questionnaires to assess pain, appetite, and activity. 7) Adjustments: If metastasis develops, consider second-line chemotherapy (e.g., metronomic therapy) or palliative care.

Pearls: 1) Always consider HSA in any middle-aged to older large-breed dog with acute collapse and hemoabdomen. 2) A splenic mass with a right atrial mass on echocardiography is highly suggestive of HSA. 3) Preoperative thoracic radiographs are essential to rule out pulmonary metastasis. 4) Doxorubicin is the most effective single agent; use it early. 5) Metronomic chemotherapy is a well-tolerated option for dogs that cannot tolerate doxorubicin. 6) For cutaneous HSA, wide surgical excision with 3 cm margins can be curative if no metastasis. Pitfalls: 1) Do not delay surgery for a ruptured splenic mass; emergency splenectomy is life-saving. 2) Avoid fine-needle aspiration of splenic masses due to risk of rupture and hemorrhage. 3) Do not rely on cytology alone for diagnosis; histopathology is mandatory. 4) Do not use corticosteroids as sole therapy; they have no effect on HSA. 5) Do not overlook DIC; treat aggressively with plasma and heparin if indicated. 6) Do not assume a splenic mass is benign; histopathology is required. 7) Do not forget to stage the disease; prognosis and treatment decisions depend on stage.

Based on Plumb's Veterinary Drug Handbook, the following protocols are used: 1) Doxorubicin: 30 mg/m² IV every 3 weeks. Administer as a slow IV infusion over 20-30 minutes with saline diuresis (5 ml/kg/hr) to reduce cardiotoxicity. Monitor for arrhythmias and extravasation. 2) Cyclophosphamide: 50-75 mg/m² PO on days 3-6 of each doxorubicin cycle (VAC protocol) or 10-15 mg/m² PO daily for metronomic therapy. Ensure adequate hydration to prevent sterile hemorrhagic cystitis. 3) Vincristine: 0.5-0.7 mg/m² IV on day 8 of VAC protocol. 4) Piroxicam: 0.3 mg/kg PO every 24 hours (metronomic). Use with caution in patients with renal disease or GI ulcers. 5) Toceranib: 2.75 mg/kg PO every other day. Monitor for GI upset, neutropenia, and proteinuria. 6) For pain: Buprenorphine 0.01-0.03 mg/kg IV/IM q8-12h; Carprofen 2.2 mg/kg PO q12h (max 14 days); Gabapentin 10-20 mg/kg PO q8-12h for neuropathic pain. 7) For DIC: Fresh frozen plasma 10-15 ml/kg IV over 2-4 hours; Heparin 200-300 IU/kg SC q8h (monitor aPTT). 8) Antiemetics: Maropitant 1 mg/kg IV/PO q24h; Ondansetron 0.5-1 mg/kg IV q8-12h. 9) Gastroprotectants: Omeprazole 1 mg/kg PO q24h; Sucralfate 0.5-1 g PO q8h. 10) Nutritional supplements: Omega-3 fatty acids (EPA/DHA) 40 mg/kg/day PO.

Key studies and consensus guidelines: 1) A landmark study by Spangler and Culbertson (1992) reported that splenic HSA has a high metastatic rate and poor survival. 2) A randomized trial by Vail et al. (1995) showed that doxorubicin-based chemotherapy significantly prolongs survival in dogs with splenic HSA compared to surgery alone (MST 172 days vs. 86 days). 3) A study by Thamm et al. (2006) evaluated metronomic cyclophosphamide and piroxicam, showing a median survival of 178 days in dogs with measurable disease. 4) The ACVIM consensus on the use of chemotherapy in veterinary oncology (2016) recommends doxorubicin as the standard of care for HSA. 5) A study by Kim et al. (2017) investigated toceranib in HSA, showing modest activity. 6) The Veterinary Cooperative Oncology Group (VCOG) has published response evaluation criteria for solid tumors, which are used in clinical trials. 7) A retrospective study by Boston et al. (2011) identified prognostic factors for splenic HSA, including stage and mitotic index. 8) A study by Mullin et al. (2016) evaluated cardiac troponin I as a biomarker for cardiac HSA, showing elevated levels in affected dogs. 9) The use of immunotherapy (e.g., eBAT, a bispecific angiotoxin) is under investigation, with a phase I trial showing some efficacy. 10) Current research focuses on targeted therapies, including inhibitors of the PI3K/Akt/mTOR pathway and anti-angiogenic agents.