What is hemangiosarcoma, and can it appear suddenly?

Hemangiosarcoma is a malignant tumor arising from the inner lining of blood vessels, commonly affecting the spleen or liver. In some cases symptoms appear suddenly, presenting as lethargy or internal bleeding. If you have concerns, consult your vet promptly.

How do vets typically confirm a diagnosis of hemangiosarcoma?

Common diagnostics include a physical examination, blood tests, abdominal ultrasound, and chest X-rays. Cytology, biopsy, and advanced imaging (CT) may also be used when needed. The final diagnosis is based on the pathology report.

What should I do if I find my pet is coughing or vomiting blood at home?

Record when it happened and how often, and take a photo or video as evidence. Contact your vet immediately to describe the situation — if there is heavy bleeding or breathing difficulty, go to an emergency clinic right away.

What does treatment and prognosis look like for hemangiosarcoma?

Treatment and prognosis vary depending on the location of the lesion, whether it has spread, and the pet's overall health. Management may involve surgery and systemic therapy alongside supportive care. It is strongly recommended to discuss an individualized treatment and monitoring plan with a veterinary oncologist.

How much do the tests and treatment usually cost?

Costs vary by clinic and region — ask your vet for an estimate before proceeding.

Disease Guide

Hemangiosarcoma in Dogs & Cats: Spleen & Liver Symptoms, Diagnosis & Treatment [2025]

Hemangiosarcoma of the spleen and liver is a highly malignant tumor that often presents as an emergency due to internal bleeding. Surgery followed by chemotherapy is recommended, though the overall prognosis remains guarded.

Take 1 minute to check the symptoms first

Last updated: 2026/01/05

Pethealthmap Editorial Team

Sources: AVMA, ACVIM, National Taiwan University Veterinary Hospital

When to See a Vet

Seek immediate emergency care

•Rapid breathing with persistent and obvious open-mouth breathing
•Coughing or vomiting large amounts of blood with clots
•Sudden collapse, loss of consciousness, or unresponsiveness

Schedule a clinic visit soon (within 24–72 hours)

•Persistent decline in energy and loss of appetite
•Rapid and significant weight loss beyond what is expected in a short period
•Recurring cough or increasingly labored breathing with higher frequency

01What symptoms indicate something is wrong?

Hemangiosarcoma in dogs and cats commonly presents with systemic weakness and symptoms related to breathing or internal bleeding. Early signs may be subtle — watch closely for how quickly they progress and any signs of hemorrhage.

Decreased energy and significantly reduced activity levels
Persistent weakness, easy fatigue, and tendency to hide
Rapid weight loss or noticeably reduced appetite over a short period
Recurring cough or occasional blood-tinged sputum — video recording is recommended
Increased respiratory rate, labored breathing, or worsening open-mouth breathing
Pale gums or changes in other mucous membrane color (signs of anemia)

Seek emergency care immediately if you notice the following symptoms:

⚠️ Rapid breathing with persistent, obvious open-mouth breathing
⚠️ Coughing or vomiting large amounts of blood, including clots
⚠️ Sudden collapse, loss of consciousness, or unresponsiveness

02How to assess abnormal signs at home? Key observations and emergency criteria

Observing and recording key changes at home helps your vet assess the situation and prioritize care. Videos and photos are often more informative than verbal descriptions.

Note when symptoms first appeared and how their frequency has changed over time
Weigh your pet at the same time each day and track the trend
Record short videos of coughing, breathing, or activity patterns for reference
Track daily food and water intake and any changes in appetite
Monitor bowel movements and urine output; watch for blood in urine or dark stools
If breathing or bleeding worsens, call your vet immediately and seek care as soon as possible

03How will the vet make a diagnosis? Common diagnostic tests

Your vet will use imaging and laboratory tests to assess the location of the lesion, whether bleeding is present, and whether the tumor has spread — then plan treatment and follow-up accordingly.

Full physical examination to assess the heart, lungs, and abdomen for enlargement or pain

Chest X-rays to identify lung lesions or pleural effusion

Abdominal ultrasound to evaluate the size and location of splenic and hepatic lesions

Fine needle aspiration or cytology to characterize the mass (if appropriate)

Blood work to assess anemia, coagulation status, and overall organ function

Advanced imaging (CT or MRI) to evaluate local invasion or distant metastasis

04How is it treated after diagnosis? Medications, dietary adjustments, and care guide

Treatment typically involves addressing the primary lesion alongside systemic support, with regular imaging and bloodwork to monitor response and quality of life.

Surgical evaluation to determine whether the splenic or hepatic lesion can be resected
Consideration of further systemic treatment based on pathology and imaging findings
Supportive care as needed, including blood transfusions, oxygen therapy, or intravenous fluids
Scheduled follow-up imaging (X-ray, ultrasound, or CT) based on the disease course
Dietary modifications, pain management, and supportive care to maintain quality of life
Referral to a veterinary oncology specialist is recommended for a long-term treatment and monitoring plan

05What should you prepare before the vet visit? Key steps to help the vet assess quickly

Write down when symptoms started, how often they occur, and how they have changed

Bring short videos or photos of coughing, breathing, or activity

Prepare a list of all current medications and supplements

Bring any previous X-ray or ultrasound reports if available

Write down the key questions you want to ask the vet

Mention the urgency of symptoms when booking so the clinic can prioritize or refer to a specialist

This content is for reference only and cannot replace a professional veterinary diagnosis. If your pet shows signs of illness, please seek veterinary care promptly.