You are petting your dog one afternoon when you notice he seems slightly off — a little slower than usual, his belly looks slightly rounder, and his gums seem paler than normal. You take him to the emergency clinic, and the veterinarian performs an ultrasound that reveals a large mass on his spleen. Before you have time to process what that means, the conversation turns to emergency surgery.

This scenario plays out thousands of times each year in veterinary emergency rooms across the country. Splenic tumors in dogs are among the most dramatic and emotionally difficult oncological situations dog owners face — not only because of the cancer itself, but because of how suddenly and urgently they can present. A dog may seem entirely healthy one day and be in life-threatening hemorrhagic shock the next, after a splenic mass ruptures and bleeds into the abdomen.

At the same time, not all splenic masses are cancer. A significant proportion are benign:  hematomas, nodular hyperplasia, hemangiomas, and many dogs who survive emergency splenectomy go on to live normal lives.

Understanding the nature of splenic tumors, what the "two-thirds rule" really means, how to interpret an ultrasound finding of a splenic mass, what surgery involves, and what realistic outcomes look like empowers you to make informed decisions for your dog — even in the middle of a crisis.

What Is the Spleen and What Does It Do?

The spleen is a large, highly vascular organ located in the left cranial abdomen, nestled against the stomach. It serves several important functions:

• Hematopoiesis: In dogs, the spleen participates in blood cell production and serves as a reservoir for red blood cells

• Immune surveillance: It filters blood, removes old or damaged red blood cells, and plays a role in immune responses

• Storage: The spleen stores a significant volume of blood and can release red blood cells into circulation in response to stress or hemorrhage

Because the spleen is so richly supplied with blood vessels, it is particularly vulnerable to tumors of vascular origin, and when vascular tumors rupture, the bleeding can be catastrophic. Dogs can survive quite well without a spleen — splenectomy is not associated with significant long-term immune deficits in dogs — but the spleen's highly vascular nature is central to understanding why splenic tumors are so dangerous and why they present the way they do.

The Two-Thirds Rule: Understanding Splenic Mass Probabilities

One of the most important clinical frameworks in veterinary oncology is the so-called "two-thirds rule" for canine splenic masses, first described by Johnson and colleagues in 1989 and consistently supported by subsequent literature:

Two-thirds of splenic masses in dogs are malignant. Of those malignancies, two-thirds are hemangiosarcoma.

Working through the math: if a dog presents with a splenic mass, approximately 45 percent of all splenic masses will be hemangiosarcoma, and approximately 20 to 22 percent will be a different malignancy (such as lymphoma, histiocytic sarcoma, or leiomyosarcoma). The remaining one-third — approximately 33 percent — will be benign lesions including hematomas, nodular hyperplasia, and hemangiomas.

However, this rule is modified by clinical context:

• In dogs presenting with hemoabdomen (blood in the abdomen) from a ruptured splenic mass, the odds of malignancy increase to approximately three-quarters

• Dogs presenting incidentally (splenic mass found during surgery or imaging for an unrelated condition) are far more likely to have a benign lesion — in one recent study, 93.9 percent of incidentally discovered splenic masses were benign

• Thrombocytopenia (low platelet count) and anemia at presentation are associated with a significantly higher probability of hemangiosarcoma versus benign lesions

• In German Shepherds, the breed most strongly predisposed to hemangiosarcoma, essentially all splenic masses should be considered hemangiosarcoma until proven otherwise

Critical Point: Gross appearance, size, and imaging characteristics of splenic masses cannot reliably distinguish benign from malignant lesions. A large, cavitated, bloody-appearing mass can be a benign hematoma. A smaller, firmer mass can be a hemangiosarcoma. Definitive diagnosis requires histopathological examination of the excised tissue. No imaging modality currently available can confidently rule in or rule out hemangiosarcoma.

Types of Splenic Masses: Benign and Malignant

Benign Splenic Lesions

Hematoma A splenic hematoma is a collection of blood within the splenic tissue, often resulting from rupture of small vessels or trauma. Hematomas can be large and blood-filled, making them visually and ultrasonographically indistinguishable from hemangiosarcoma. They are one of the most common benign splenic lesions in dogs. Complete surgical excision is curative.

Nodular Hyperplasia Nodular hyperplasia (also called regenerative hyperplasia or benign nodular transformation) is extremely common in older dogs and represents abnormal but non-cancerous overgrowth of splenic tissue. It frequently coexists with hematomas and can create complex, multi-nodular splenic architecture on ultrasound. These lesions are benign and splenectomy is curative.

Hemangioma A hemangioma is a benign tumor of blood vessels. It is histologically similar to hemangiosarcoma in its vascular composition but lacks the malignant cytological features. Complete excision is curative.

Splenic Abscess Bacterial infection of the spleen, creating a walled-off collection of pus. Uncommon; presents with systemic illness, fever, and imaging findings suggesting an infected mass. Requires splenectomy plus systemic antibiotics.

Extramedullary Hematopoiesis When bone marrow is under stress, the spleen can take over blood cell production. This creates nodular changes within the spleen that are not neoplastic.

Malignant Splenic Tumors

Hemangiosarcoma (HSA) — The Most Common Splenic Malignancy

Hemangiosarcoma is a highly aggressive malignancy originating from the endothelial cells that line blood vessels. It is the most important and most dangerous splenic tumor in dogs, representing approximately two-thirds of all malignant splenic masses. Every aspect of its biology is hostile: it grows rapidly, invades surrounding structures, forms blood-filled cavities prone to rupture, and metastasizes early — with microscopic metastatic disease in the liver, lungs, mesentery, and other organs almost invariably present at the time of diagnosis, even when imaging appears clear.

HSA is discussed in detail throughout this guide as the primary focus of splenic tumor management.

Lymphoma

Splenic lymphoma can present as diffuse splenic enlargement (splenomegaly) or as discrete nodular masses. Unlike HSA, splenic lymphoma is frequently part of systemic, multicentric lymphoma involving lymph nodes and other organs. Treatment is primarily chemotherapy (CHOP-based protocols) rather than surgery in most cases. Prognosis is variable but can be significantly better than HSA for certain subtypes.

Histiocytic Sarcoma

Histiocytic sarcoma involving the spleen is an aggressive malignancy of dendritic cell or macrophage origin. It can present as splenic masses and is strongly associated with certain breeds, particularly Bernese Mountain Dogs, Flat-Coated Retrievers, Rottweilers, and Golden Retrievers. Prognosis is poor. Treatment involves surgery and chemotherapy (CCNU/lomustine-based protocols).

Leiomyosarcoma

A sarcoma arising from smooth muscle cells within the spleen. Less aggressive than HSA in many cases, though still malignant. May have a somewhat better prognosis than HSA when completely excised.

Mast Cell Tumor

Mast cell tumor involving the spleen is most often part of systemic or visceral mast cell disease rather than a primary splenic tumor. Treatment involves splenectomy plus systemic therapy (Palladia/toceranib or other protocols). Prognosis depends on the degree of systemic involvement.

Plasma Cell Tumor / Multiple Myeloma

Rare primary splenic presentation. Part of a broader discussion of plasma cell neoplasia.

Breeds at Highest Risk

Hemangiosarcoma in dogs has a strong breed predisposition, consistent with an inherited genetic component to risk:

• German Shepherd Dog — highest reported risk; essentially all presentations should be assumed HSA pending histopathology

• Golden Retriever — markedly elevated risk; Golden Retrievers represent a disproportionate share of HSA diagnoses nationally

• Labrador Retriever — elevated risk

• Boxer — elevated risk

• Bernese Mountain Dog — elevated risk (also high risk for histiocytic sarcoma)

• Flat-Coated Retriever — elevated risk for both HSA and histiocytic sarcoma

• Skye Terrier — elevated risk

• Portuguese Water Dog — elevated risk

Large breed dogs are significantly more commonly affected than small breed dogs, though splenic HSA does occur in small breeds as well. One retrospective study found that small and large breed dogs with splenic HSA treated with splenectomy and chemotherapy had similar median survival times (116 days for small breed vs. 97 days for large breed), indicating that prognosis is equally poor regardless of size.

HSA most commonly affects middle-aged to older dogs, with a mean age at diagnosis of 8 to 10 years.

How Splenic Tumors Present: From Incidental Finding to Emergency

The Silent Period

This is one of the most difficult aspects of splenic tumors: the spleen is a retroperitoneal organ, not easily palpated in many dogs, and splenic masses can grow to enormous size with no outward signs. A dog with a softball-sized splenic mass may eat normally, play normally, and show no external abnormalities whatsoever.

During this silent period, the only way to detect a splenic mass is through routine abdominal palpation by an experienced veterinarian (large masses are sometimes palpable), or through screening ultrasound. For high-risk breeds — particularly German Shepherds and Golden Retrievers over age 8 — many oncologists and internists advocate for annual or semi-annual abdominal ultrasound as a screening measure.

Vague Prodromal Signs

Some dogs show subtle, non-specific signs in the weeks to months preceding rupture:

• Intermittent lethargy or fatigue that owners attribute to aging

• Reduced exercise tolerance

• Occasional episodes of weakness or wobbly movement (mini-bleeds that are self-contained)

• Mildly distended abdomen

• Reduced appetite

These signs are so nonspecific that they are rarely recognized as splenic tumor symptoms until after the diagnosis is made. In retrospect, many owners recognize that their dog had these signs for weeks before the emergency.

Acute Collapse: The Emergency Presentation

The most dramatic and common presentation of splenic hemangiosarcoma is acute collapse due to hemoabdomen — internal hemorrhage from a ruptured splenic mass. This can occur with no warning whatsoever, and it constitutes a life-threatening emergency.

Signs of acute splenic rupture:

• Sudden collapse or profound weakness

• Pale, white, gray, or blue-tinged gums (pallor indicating severe anemia/blood loss)

• Rapid, weak pulse

• Abdominal distension — a "pot-bellied" appearance developing over minutes to hours

• Rapid, labored breathing

• Severe lethargy — dog may be unable to stand

• Prolonged capillary refill time (press gums — normal refill is < 2 seconds)

This is a veterinary emergency. A dog showing these signs requires immediate emergency care — do not wait.

At the emergency clinic, a rapid assessment will include:

• Packed cell volume (PCV) or complete blood count to assess the degree of anemia

• Abdominal ultrasound to identify free fluid (blood) and the presence of a splenic mass

• Abdominal tap (abdominocentesis) — blood that does not clot in a syringe confirms hemoabdomen

• Coagulation testing — DIC (disseminated intravascular coagulation) can complicate HSA

• Thoracic radiographs to screen for pulmonary metastasis

• Cardiac evaluation — HSA commonly involves both the spleen and the right atrium/auricle of the heart

The patient will typically be stabilized with IV fluids and/or blood transfusion before proceeding to surgery.

Incidental Discovery

A smaller proportion of splenic masses are discovered incidentally — during routine wellness imaging, pre-anesthetic workup, or during abdominal surgery for another reason. As noted above, incidentally discovered masses are much more likely to be benign. These dogs have the significant advantage of not being in crisis at the time of diagnosis, allowing more time for workup, owner discussion, and surgical planning.

Diagnosis

Imaging

Abdominal Ultrasound Ultrasound is the primary imaging modality for evaluating the spleen. It can identify the presence, size, and internal architecture of splenic masses, and can detect free abdominal fluid. However — and this is critically important — ultrasound cannot reliably differentiate benign from malignant splenic lesions. Hematomas, nodular hyperplasia, and hemangiosarcoma all overlap considerably in their ultrasound appearance. A heterogeneous, cavitated, blood-filled mass could be any of these diagnoses. This limitation is fundamental to the clinical decision-making around splenic masses.

Contrast-enhanced ultrasound (CEUS) using microbubble contrast agents has shown some ability to better characterize splenic lesions — malignant lesions, including HSA, tend to show hypoechogenicity in all filling phases and tortuous, aberrant vessels — but overlap with benign hematomas remains significant, and CEUS is not universally available.

CT (Computed Tomography) CT provides superior spatial resolution compared to ultrasound, better characterizes the full extent of the primary splenic mass, and is more sensitive for detecting small pulmonary metastatic nodules than plain radiographs. For dogs in stable condition where metastatic disease needs to be thoroughly assessed before surgery, CT of the chest and abdomen is increasingly the preferred staging modality. Contrast-enhanced CT can also provide some additional characterization of splenic lesions, though it cannot definitively distinguish HSA from benign lesions.

Thoracic Radiographs Three-view thoracic radiographs are standard for evaluating pulmonary metastasis. They are less sensitive than CT for detecting small pulmonary nodules, but are widely available and appropriate for initial staging, particularly in emergency situations.

MRI MRI offers excellent soft tissue contrast and may have some emerging utility in distinguishing benign from malignant splenic lesions, but its limited availability, cost, and the need for prolonged anesthesia restrict its routine use in this setting.

Bloodwork

A complete blood count (CBC), serum chemistry, and coagulation panel are essential components of the diagnostic workup:

• Anemia: Regenerative (responsive) anemia from blood loss is common in dogs with splenic HSA. Severe, non-regenerative anemia may indicate chronic disease

• Thrombocytopenia: Low platelet count is significantly associated with hemangiosarcoma versus benign splenic disease in multiple studies. Large breed dogs with splenic HSA are approximately 8.4 times more likely to have thrombocytopenia than those with non-HSA splenic malignancy

• Schistocytes: Fragmented red blood cells on blood smear — a sign of DIC, which can complicate HSA

• Coagulation abnormalities: Prolonged PT, aPTT, elevated fibrin degradation products — indicate DIC risk

• Nucleated red blood cells: Often elevated in dogs with splenic HSA

Why Pre-Surgical Fine Needle Aspirate Is Not Performed

Fine needle aspirate (FNA) of splenic masses is generally not recommended before surgery for two important reasons. First, the highly vascular and fragile nature of these masses creates a significant hemorrhage risk. Second, cytology from splenic FNA has poor diagnostic accuracy for distinguishing HSA from benign lesions — the blood-filled nature of the tissue makes interpretation unreliable. Definitive diagnosis requires histopathological examination of the excised spleen.

Staging

The clinical staging system for splenic hemangiosarcoma divides disease into three stages:

Stage at diagnosis is among the most powerful predictors of outcome. Median survival time for Stage I disease has been reported at approximately 5.5 months, dramatically better than the approximately 0.9 months reported for untreated Stage III disease. However, because microscopic metastases are almost universally present at diagnosis for HSA, even when imaging is clear, the vast majority of dogs are functionally Stage II or III, even when staged as Stage I based on imaging.

An important additional staging consideration is cardiac involvement. Hemangiosarcoma has a strong predisposition for the right atrium and right auricle of the heart. Cardiac HSA can occur concurrently with splenic HSA or can develop as a subsequent site of disease. Echocardiography — cardiac ultrasound — should be part of the staging workup for all dogs with confirmed or suspected splenic HSA.

Treatment

Surgery: Splenectomy

Splenectomy — complete surgical removal of the spleen — is the cornerstone of treatment for splenic masses of all types. For dogs presenting in hemoabdomen, emergency splenectomy is often both the diagnostic and the life-saving intervention. For stable dogs with incidentally discovered masses, elective splenectomy allows for planned surgery under optimal conditions.

What surgery involves: The surgeon makes a midline abdominal incision, carefully ligates the splenic vessels, removes the entire spleen, and closes the abdomen. The entire spleen — not just a portion of it — is removed and submitted for histopathology. Critically, the surgeon also carefully examines the entire abdomen for evidence of metastatic disease: the liver (most common metastatic site), mesentery, omentum, lymph nodes, and other surfaces. Any suspicious lesions on other organs are biopsied. This is important because what appears to be a hepatic metastatic nodule on gross examination may actually be a benign hematoma or extramedullary hematopoiesis, and conversely, what appears to be normal liver may harbor microscopic HSA.

Splenectomy alone without chemotherapy for confirmed splenic HSA results in median survival times of approximately 19 to 86 days, with fewer than 10 percent of dogs surviving one year. The reason is not the surgery itself — splenectomy successfully removes the primary tumor — but the near-universal presence of microscopic metastatic disease that rapidly progresses after surgery.

For benign lesions, splenectomy is curative, and dogs return to normal life expectancy.

Adjuvant Chemotherapy

Because microscopic metastasis is present in virtually all cases of splenic HSA at the time of diagnosis, adjuvant systemic chemotherapy is recommended following splenectomy for all dogs with confirmed or suspected HSA. 

The goal is not a cure; there is no cure for splenic HSA, but meaningful prolongation of survival and maintenance of quality of life.

Doxorubicin (Adriamycin) — Standard of Care

Doxorubicin is the most extensively studied and most commonly recommended chemotherapeutic agent for canine HSA. It is administered intravenously every 2 to 3 weeks, typically for 5 cycles. Median survival times with splenectomy plus doxorubicin-based protocols range from approximately 4 to 6 months across multiple studies, compared to approximately 1 to 2 months with surgery alone.

Doxorubicin carries the risk of cumulative cardiotoxicity — it can damage the heart muscle with repeated dosing. Cardiac function (echocardiography) is typically assessed before initiating therapy. Common side effects include gastrointestinal upset (nausea, vomiting, diarrhea), bone marrow suppression (reduced white blood cell counts), and, with the cumulative cardiac limit, cardiomyopathy.

Combination Protocols

Various combination chemotherapy protocols have been studied, including vincristine + doxorubicin + cyclophosphamide (VAC), ifosfamide + doxorubicin, and doxorubicin + cyclophosphamide + minocycline. None have consistently demonstrated superior survival over doxorubicin alone, and combination protocols often carry higher toxicity. Doxorubicin as a single agent remains the most practical and widely used approach.

Carboplatin

Carboplatin is an alternative platinum-based chemotherapy agent studied in dogs who cannot receive doxorubicin (due to pre-existing cardiac disease or poor cardiac function). Retrospective data suggest survival outcomes broadly comparable to doxorubicin in some studies, though the evidence base is smaller. It is administered every 3 weeks.

Metronomic Chemotherapy

Metronomic chemotherapy — continuous low-dose oral chemotherapy with anti-angiogenic and immunomodulatory effects — is an increasingly used alternative or adjunct approach for dogs with HSA, particularly those who cannot tolerate or whose owners decline standard IV chemotherapy. Common metronomic protocols include low-dose cyclophosphamide (approximately 10–15 mg/m² daily or every other day) combined with an NSAID such as piroxicam.

A landmark study by Lana and colleagues (2007) found that a metronomic protocol of cyclophosphamide, etoposide, and piroxicam resulted in median survival times of 178 days — comparable to or exceeding results reported with doxorubicin in historical controls. More recent data continue to support metronomic approaches as a reasonable alternative, particularly for clients seeking lower-intensity treatment options. Side effects are generally mild, including gastrointestinal upset and a risk of sterile hemorrhagic cystitis with cyclophosphamide (mitigated by concurrent furosemide or adequate hydration). Regular blood work monitoring is still required.

COX-2 Inhibitors / NSAIDs

Cyclooxygenase-2 (COX-2) is overexpressed in canine HSA tissue, and NSAIDs that inhibit COX-2 — particularly piroxicam and deracoxib — have been studied both as stand-alone agents and as components of metronomic or combination protocols. A pilot study combining doxorubicin with deracoxib (a selective COX-2 inhibitor) post-splenectomy achieved an overall median survival of 150 days with good tolerability. NSAIDs are generally incorporated into most adjuvant and metronomic protocols as an accessible, well-tolerated component.

Toceranib (Palladia)

Toceranib phosphate, a receptor tyrosine kinase inhibitor licensed for canine mast cell tumor treatment, inhibits multiple kinases relevant to HSA biology — including KIT, PDGFR, and VEGFR-2. Canine HSA cells express these kinases at elevated levels compared to normal splenic tissue. Studies evaluating toceranib as maintenance therapy following splenectomy and primary chemotherapy are ongoing, and it is increasingly used in clinical practice. Full efficacy data for splenic HSA specifically are still being generated.

Palliative Options for Non-Surgical Candidates

Dogs with confirmed distant metastasis, significant comorbidities precluding anesthesia, or whose owners decline surgery may still be offered palliative systemic therapy. Chemotherapy in the setting of gross metastatic disease is generally less effective — survival is measured in weeks — but can maintain quality of life for a period. Yunnan Baiyao, a traditional Chinese herbal preparation with hemostatic properties, is frequently used as a supportive measure to help manage the risk of ongoing splenic bleeding; while not a cancer treatment, it is generally considered safe and may provide some clinical benefit in reducing bleeding episodes.

Prognosis

The Honest Overview

The prognosis for splenic hemangiosarcoma is poor, and dog owners need to understand this honestly while also recognizing what treatment can and cannot offer.

There is no cure for splenic HSA. Even with optimal treatment, splenectomy plus adjuvant chemotherapy, median survival is approximately 4 to 6 months, and fewer than 10 percent of dogs are alive at one year. This is not because treatment fails to work; it is because the disease is almost always systemically disseminated at diagnosis, microscopic metastases are too small to detect or treat, and HSA biology is intrinsically aggressive.

What treatment does accomplish:

• Surgery removes the source of life-threatening hemorrhage and extends survival meaningfully compared to no treatment

• Chemotherapy further extends median survival by 2 to 4 months compared to surgery alone

• Quality of life during treatment is generally good — dogs typically feel and act well between treatment cycles

Survival Time Summary

Staging Impact

Stage at diagnosis meaningfully affects outcome:

• Stage I (confined, intact spleen): median survival approximately 5.5 months; best prognosis

• Stage II (ruptured or nodal involvement): median survival 1–3 months (surgery alone); extended with chemotherapy

• Stage III (distant metastasis): median survival < 1 month without treatment; weeks to a few months with palliative therapy

Negative Prognostic Factors

• Stage III (distant metastasis) at diagnosis

• Ruptured tumor with hemoabdomen at presentation (Stage II)

• Concurrent cardiac HSA

• Severe anemia and thrombocytopenia at diagnosis

• Elevated DIC parameters

• Strong CD31 expression on histopathology (emerging research)

For Benign Lesions

Dogs with benign splenic masses: hematomas, nodular hyperplasia, and hemangiomas have an excellent prognosis following splenectomy. Surgery is curative. Life expectancy returns to normal for age and breed, with no ongoing oncological concern. This is the reason that pursuing splenectomy even in the face of uncertain prognosis is often the right decision — because a meaningful proportion of dogs will have benign disease and live normal lives.

Emerging Treatments and Research

Immunotherapy and Biological Agents

eBAT (EGF-bispecific angiotoxin) is an experimental recombinant protein under study at the University of Minnesota that targets receptors expressed on HSA tumor vasculature. Early data suggested meaningful activity, and it represents one of the most promising experimental agents for HSA. Clinical trials have been ongoing for several years.

I'm-Yunity (polysaccharopeptide / PSP from Coriolus versicolor / Turkey Tail mushroom) gained attention after a small clinical trial by Doris Lau and colleagues at the University of Pennsylvania found that dogs with HSA treated with PSP after splenectomy had significantly longer median time to metastasis compared to historical controls (median 199 days vs. 30 days in one cohort). A published case report described a dog with splenic HSA treated with metronomic chlorambucil plus I'm-Yunity achieving 24-month survival. These are preliminary findings from small studies, and PSP is not a proven treatment, but it is well-tolerated and increasingly discussed as an adjunct alongside conventional therapy.

Precision Medicine and Genomic Profiling

A 2023 Tufts University study profiling genomic alterations in canine splenic HSA found that somatic mutations in TP53, NRAS, and PIK3CA were most common. Survival was associated with the presence of metastases at diagnosis and germline variants in SETD2 and NOTCH1. This work provides a foundation for precision oncology approaches — matching targeted therapies to specific mutational profiles — that may eventually improve outcomes. Liquid biopsy approaches (detecting tumor DNA in blood) are also under active investigation as potential screening tools for high-risk breeds.

Targeted Antiangiogenic Therapy

Because HSA is fundamentally a tumor of blood vessels, anti-angiogenic strategies are biologically rational. VEGF, FGF, and angiopoietin signaling are dysregulated in canine HSA. Agents targeting VEGFR-2 and PDGFR (including toceranib) are being studied. The consistent challenge is that even when these pathways are inhibited, the tumor has sufficient redundancy to escape single-agent targeted therapy.

Losartan

Losartan, an angiotensin II receptor blocker (commonly used for blood pressure), has been investigated for potential anti-tumor effects based on its ability to reduce desmoplastic tumor stroma and improve drug delivery. It is under evaluation as a palliative adjunct for dogs with HSA.

Integrative and Supportive Care

Yunnan Baiyao

This traditional Chinese herbal hemostatic preparation is widely used in dogs with HSA to help manage the risk of bleeding from the primary or metastatic tumor. While not an anti-cancer treatment, Yunnan Baiyao has demonstrated platelet-aggregating and hemostatic properties in laboratory studies, and many oncologists recommend it as an adjunct. It is available in capsule form and is generally very well-tolerated. The most common dosing protocol used in dogs is weight-based and typically involves daily administration. Your oncologist can provide appropriate dosing guidance.

Fish Oil (EPA/DHA Omega-3 Fatty Acids)

Omega-3 supplementation with EPA and DHA has anti-inflammatory and potential anti-tumor properties. It is safe, accessible, and is frequently recommended as part of an integrative cancer care protocol alongside conventional therapy.

Nutrition

Maintaining good nutritional status supports immune function, healing from surgery, and tolerance of chemotherapy. A high-quality, protein-rich diet is appropriate for most dogs with HSA. Some integrative oncologists recommend a lower-carbohydrate, higher-protein and fat diet based on the principle that cancer cells preferentially use glucose. A veterinary nutritionist can provide individualized guidance.

Monitoring During Treatment

Dogs receiving adjuvant chemotherapy require structured monitoring:

• Complete blood count before each chemotherapy cycle (to assess bone marrow tolerance)

• Echocardiogram before starting doxorubicin and periodically throughout (cardiac function monitoring)

• Thoracic radiographs or CT every 2 to 3 months to monitor for pulmonary metastasis

• Abdominal ultrasound every 2 to 3 months to monitor for new or enlarging metastatic lesions

• Regular assessment of the quality of life

Making the Decision: Surgery in an Emergency

One of the most difficult aspects of splenic HSA is that the decision about surgery often must be made in an emergency setting, while the dog is in crisis, without a confirmed diagnosis, without the owner having had time to research or process the situation.

Key points to help guide this decision:

Arguments for emergency splenectomy:

• Without surgery, a dog with an active hemoabdomen will die — either from ongoing hemorrhage or from re-rupture after stabilization

• A meaningful proportion of masses are benign — surgery may be curative

• Surgery provides the only tissue for histopathological diagnosis — you cannot know what you are dealing with without it

• Even for dogs with HSA, surgery meaningfully extends survival and provides good quality of life for months

Arguments for a more conservative approach or euthanasia:

• If pre-existing conditions (severe cardiac disease, advanced metastatic disease, systemic organ failure) make anesthesia and surgery prohibitively risky, proceeding may cause suffering without benefit

• If the dog has a very poor baseline quality of life or significant comorbidities that would limit survival regardless of the splenic lesion, aggressive intervention may not serve the dog's interests

• Financial constraints are a real consideration: emergency splenectomy plus staged diagnostics and chemotherapy represent a significant cost

Ask your emergency veterinarian: "What do the bloodwork and imaging suggest about whether this is likely benign or malignant? What is the anesthetic risk given my dog's current condition? What is a realistic range of outcomes if we proceed with surgery, and what is the timeline?"

There is no universally right answer. Choosing to pursue surgery is not foolish optimism. Choosing not to pursue surgery — or choosing euthanasia — is not giving up. These are deeply personal decisions made under genuine uncertainty, and any choice made from a place of love and information is the right one for that family.

Frequently Asked Questions

My dog was just diagnosed with a splenic mass on ultrasound. Does this mean he has cancer?

Not necessarily — and this is genuinely important to hold onto. Approximately one-third of all splenic masses are benign, and that proportion rises substantially for masses discovered incidentally (without active bleeding or crisis). You cannot know whether a splenic mass is benign or malignant from ultrasound alone. The only way to know is through histopathological examination after surgical removal. For many families, the uncertainty about whether the mass is benign is itself a significant reason to proceed with surgery.

My dog just collapsed and was taken to the emergency clinic with a bleeding splenic mass. What are the chances it is cancer?

When a dog presents with hemoabdomen (bleeding into the abdomen) from a ruptured splenic mass, the probability of malignancy rises to approximately 70 to 75 percent. This is higher than the 67 percent overall average because rupture is more common with malignant tumors. However, 25 to 30 percent of dogs in this scenario have benign masses, and surgery will be curative for them. This information may help with the decision to proceed with emergency surgery.

The surgeon said she couldn't tell just by looking at the spleen whether it was cancer. Is that normal?

Yes, absolutely normal and important to understand. Gross appearance — size, color, internal structure — cannot reliably distinguish hemangiosarcoma from benign hematomas. Both can appear as large, dark, blood-filled, cavitated masses. The surgeon is not being evasive; she genuinely cannot know without histopathology. This is one of the most consistent findings in the veterinary literature: "the gross appearance of the primary mass at the time of surgery does not correlate with malignancy." The entire spleen must be sent to the pathologist.

How long after surgery until we get the histopathology results?

Typically, 5 to 10 business days, depending on the laboratory. If immunohistochemistry (IHC) is needed to confirm the diagnosis, results may take a few days longer. Many owners find this waiting period intensely anxious. Your oncologist or surgeon can tell you when to expect results and how they will communicate them to you.

My dog had splenectomy and it came back as hemangiosarcoma. The oncologist is recommending chemotherapy. Is it worth it?

This is a deeply personal decision with no universally right answer. What chemotherapy (primarily doxorubicin) offers is a meaningful extension of survival — from a median of approximately 1 to 2 months with surgery alone to approximately 4 to 6 months with surgery plus chemotherapy. During that time, most dogs feel and act well between treatments. Chemotherapy does not cause the same severity of side effects in dogs as in humans. The honest framework is: chemotherapy gives most dogs a few additional good months with their families. Whether those months — and the treatment visits and monitoring they involve — are the right choice depends on your dog's overall health, temperament, and your family's values and circumstances.

Can I skip IV chemotherapy and do something lower-intensity?

Yes. Metronomic chemotherapy — low-dose oral cyclophosphamide plus an NSAID — has shown comparable survival outcomes to doxorubicin in some studies and is a reasonable alternative, particularly for owners who prefer a lower-intensity approach or whose dogs cannot tolerate IV doxorubicin. Discuss this with a veterinary oncologist. There is also growing interest in PSP/I'm-Yunity as an adjunct, though the evidence base is more limited.

Does it matter whether my dog's spleen ruptured before surgery?

Having a ruptured spleen at the time of diagnosis classifies the dog as Stage II rather than Stage I. Stage II carries a shorter median survival than Stage I. However, rupture does not eliminate the possibility of meaningful survival with treatment, and emergency splenectomy remains appropriate for most dogs in reasonable overall condition.

My dog has been diagnosed with HSA. How will I know when it is time to consider euthanasia?

Quality of life assessment tools provide a structured framework for this question. The HHHHHMM Scale (assessing Hurt, Hunger, Hydration, Hygiene, Happiness, Mobility, and More good days than bad) developed by Dr. Alice Villalobos is widely used. Signs that the disease is advancing and quality of life is declining include: persistent weakness or inability to rise, recurrent episodes of collapse from re-bleeding, labored breathing from pulmonary metastasis, significant loss of appetite, disorientation, or apparent distress. Your oncologist can help you monitor for these signs. Many families find that having this conversation proactively — while their dog is still doing well — helps them feel more prepared when the time comes. Choosing a peaceful death before suffering becomes unmanageable is one of the most profound acts of love and advocacy in a dog owner's life.

Peer-Reviewed References

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2. Ziogaite B, Contreras ET. Incidence of splenic malignancy and hemangiosarcoma in dogs undergoing splenectomy surgery at a surgical specialty clinic: 182 cases (2017–2021). PLOS ONE, 19(12):e0314737, 2024. https://pmc.ncbi.nlm.nih.gov/articles/PMC11614263/

3. Chu K-T, Nekouei O, Sandy JR. Histopathological grading, clinical staging and CD31 expression of canine splenic hemangiosarcoma. Veterinary Sciences, 10(3):190, 2023. https://pmc.ncbi.nlm.nih.gov/articles/PMC10054225/

4. Estabrooks T, Gurinovich A, Pietruska J, et al. Identification of genomic alterations with clinical impact in canine splenic hemangiosarcoma. Veterinary and Comparative Oncology, 21(4):623–633, 2023. https://pubmed.ncbi.nlm.nih.gov/37734854/

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9. Hammer AS, Couto CG, Filppi J, Getzy D, Shank K. Efficacy and toxicity of VAC chemotherapy (vincristine, doxorubicin, and cyclophosphamide) in dogs with hemangiosarcoma. Journal of Veterinary Internal Medicine, 5(3):160–166, 1991. https://pubmed.ncbi.nlm.nih.gov/1875368/

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18. Dervisis NG, Dominguez PA, Newman RG, Cadile CD, Kitchell BE. Treatment with DAV for advanced-stage hemangiosarcoma in dogs. Journal of the American Animal Hospital Association, 47(3):170–178, 2011. https://pubmed.ncbi.nlm.nih.gov/21511892/

19. Lucroy MD, Suckow MA, Van Dyke MF, et al. Hemangiosarcoma in a dog: Unusual presentation and increased survival using a complementary/holistic approach combined with metronomic chemotherapy. PMC, PMC6005304, 2018. https://pmc.ncbi.nlm.nih.gov/articles/PMC6005304/

20. Hemangiosarcoma in Dogs. Cornell Richard P. Riney Canine Health Center, 2024. https://www.vet.cornell.edu/departments-centers-and-institutes/riney-canine-health-center/canine-health-information/hemangiosarcoma-dogs

21. Withrow SJ, Vail DM, Page RL (Eds.). Withrow & MacEwen's Small Animal Clinical Oncology, 5th ed. Elsevier Saunders, 2013. https://www.sciencedirect.com/book/9781437723625/withrow-and-macewen-s-small-animal-clinical-oncology

 

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This article is intended for educational purposes only and does not constitute veterinary medical advice. Always consult a licensed veterinarian or board-certified veterinary oncologist for guidance specific to your dog's health needs.