Cancers of the heart are uncommon in dogs and cats. When they do occur, it’s important to differentiate a tumor from other conditions that could cause generalized or focal enlargement of the heart and cardiovascular symptoms.

Which cancers occur in cardiac tissues?

A cancerous lesion based at the heart could be a primary tumor, or due to metastasis. 

Primary tumors that occur at the heart include:

• Hemangiosarcomas—the most common heart cancer in dogs, usually occurring at the right atrium. These occur most frequently in larger dogs with longer noses, such as Golder Retrievers, Doberman Pinschers, and German Shepherds.

• Chemodectomas, also known as aortic body tumors or heart base tumors. Generally thought to be slow-growing, these tumors occur most commonly in brachycephalic breeds like Boxers, Bulldogs, and Boston Terriers.

• Myxomas.

• Sarcomas.

• Ectopic thyroid tumors.

• Lymphoma/lymphosarcoma—the most common heart cancer in cats.

Other cancers are possible, but these are the most commonly diagnosed types. Breeds may vary as noted above, but most pets with tumors of the heart are middle-aged or older. 

How are heart tumors diagnosed?

If slow-growing, tumors near the heart base are often an incidental finding, seen on thoracic radiographs that are taken for another reason.

Other times, diagnostics are pursued because of clinical symptoms—which are often sudden in onset.

Once a mass is large enough to push on the heart and major blood vessels, many cardiovascular symptoms are possible, such as:

• Coughing

• Ascites

• Lethargy

• Weakness

• Vomiting

• Loss of appetite

• Difficulty breathing

• Collapse

• Sudden death

Note: If a dog presents with some of these symptoms, especially sudden weakness and collapse, a quick ultrasound scan may help to identify pericardial effusion and aid in guiding a needle for emergency pericardiocentesis.

Finding heart masses early

As with most cancers and disease processes, discovering a problem earlier rather than later can allow for more treatment options.

General screening radiographs or ultrasound checks—such as with a senior wellness health check—can be a good opportunity to discover heart base tumors before they cause cardiovascular dysfunction and symptoms.

An echocardiogram performed via ultrasound can help to provide more information on the location, size, and invasiveness of the mass. 

In some cases, a presumptive diagnosis may be made based on the appearance and location of the mass on an ultrasound study, along with the patient’s signalment. If possible to perform without undue risk, an ultrasound-guided aspirate of the mass can provide more information about which type of tumor is present.

Treatment options for cancers of the heart

Treatment will be based on the type of neoplasia, how fast the mass is growing, whether metastasis is present, and whether or not the pet is symptomatic.

When a tumor of the heart is diagnosed, a good next step is to screen for metastasis and concurrent conditions via chest x-rays (if not already done), bloodwork, lymph node evaluation, and abdominal ultrasound.

Once a diagnosis is made, treatment options may include:

• Periodic monitoring with a cardiologist (especially for slow-growing chemodectomas/heart base tumors) prior to pursuing more invasive treatments.

• Surgery to remove the tumor.

• Pericardiectomy to remove the pericardium and prevent life-threatening cardiac tamponade or pericardial effusion. 

(A pericardiocentesis may be necessary on an emergency basis prior to diagnostics in a pet who presents with acute symptoms. After that, a planned pericardiectomy can help to prevent further emergency episodes of fluid buildup around the heart.)

• Chemotherapy, often in conjunction with surgery.

• Radiation therapy—either conventional, or via Cyberknife therapy.

Even though cancers of the heart are uncommon in pets, they can be scary to pet owners because of the possibility of sudden onset of serious clinical symptoms (especially with hemangiosarcomas).

By performing diagnostics, referring to specialists as needed, and giving your clients as much information as possible, you can help them make an informed decision for their pet.

Disclaimer: This article is for general informational purposes only, and not intended as a guide to the medical treatment of any specific animal.

Written by: Dr. Tammy Powell, DVM