The Role of Radiation for Heart and Heart-Base Tumors in Small Animals

By Lyndsay Kubicek, DVM, DACVR (Radiation Oncology)

Tumors of the pericardium, heart base and myocardium are rare in veterinary medicine as is our ability to histologically diagnose antemortem. Cardiac tumors occur most frequently in middle-aged to older (7 to 15 years) dogs. Breeds reported to be at increased risk or predisposed for cardiac hemangiosarcoma include the German shepherd dog and golden retriever. Aortic body tumors occur most commonly in older brachycephalic dogs, including boxers, Boston terriers, English bulldogs, and German shepherd dogs.

Cancer of the heart may occur intracavitary, intramural, in pericardial locations, or at the heart base. The most common primary heart tumor in the dog is hemangiosarcoma, followed by aortic body (a.k.a. heart base) tumors (chemodectoma, paraganglioma).

Tumors involving the heart cause varied clinical signs, highly dependent on their anatomic location. The most common signs are associated with one of four disruptions of function: the mass causing an outflow obstruction into or out of the heart, external compression of the heart that impedes filling, disruption of normal heart rhythm, and decreased myocardial contractility secondary to infiltration or ischemia.

Frontline therapy is geared towards managing the clinical signs associated with the tumor as a sole therapy or to stabilize for definitive therapy. Medical management can control clinical signs for a period of time, however without treating the underlying tumor, such therapies typically fail within months of diagnosis. Surgical resection of primary cardiac tumors may be attempted in a small amount of well-selected cases. In setting client expectations, surgical excision of right auricular canine hemangiosarcoma should be considered a palliative procedure due to the high probability of metastatic disease. The reported mean survival times of canine cardiac hemangiosarcoma patients treated with surgical resection alone range from 46 days to 5 months. With the addition of adjuvant chemotherapy, significant improvement in survival time can be appreciated following surgery with a reported mean of 164 days.

Pericardectomy can be used prophylactically or symptomatically for pericardial effusion in the treatment of dogs with aortic body tumors. Such intervention in dogs results in a significant improvement in survival times (median survival 730 days) compared to those that did not have a pericardectomy (median survival 42 days).

The role of targeted therapies such as Palladia (toceranib phosphate) has not been published in peer-reviewed journals to date, however clinically this treatment is used in practice with promising results of 12-18 months of control. This drug is generally well tolerated, however there are side effects noted. Palladia can be used alone or in combination with surgery and/or radiation therapy.

Radiation is the newest treatment option for heart base tumors. In general there are two types of radiation that have been described in the literature thus far. Stereotactic radiation therapy (SRT) is the newest and most convenient treatment available for cancers adjacent to critical structures such as the nervous system, heart and lungs. SRT involves the delivery of 1-5 precisely delivered ablative doses of radiation. The only publication is a proof of principle for neuromuscular blockade with breath holding for delivery of SRT in 4 dogs. Although the aim of the study was anesthesia related, clinically we feel tumor shrinkage is achieved within the first few months with control for 18-24 months. This therapy is well tolerated and can be repeated.

Photo: courtesy of Pamela J. Mouser, DVM, MS, DACVP. Labels: C is chemodectoma H is hemangiosarcima

When SRT is not recommended or available, full-course radiation therapy is an alternative. Full-course radiation is given once a day (Monday through Friday) for 3.5 weeks (18 treatments total). A case report of full-course radiation showed a progression free time of 32 months. At recurrence the patient was treated with pericardectomy and additional radiation therapy and was alive and doing well 42 months following initial radiation treatment.

A recently published pilot study showed palliative radiation is safe and effective at significantly reducing the need for pericardiocentesis for right atrial masses with hemorrhagic pericardial effusion. In the 6 cases the median survival time was 79 days following a single dose of radiation, however the need for pericardiocentesis was reduced significantly. Clinically we have used a 4-fraction protocol (once weekly for 4 weeks) in combination with chemotherapy resulting in survival times of 6-8 months.

In conclusion, although the outcomes differ between right auricular and heartbase tumors, we now have the ability to improve quality of life and prolong survival times in such patient populations. We are eager to see future research for the role of radiation in the management of right auricular and heartbase tumors.



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J Vet Cardiol. 2017 Apr;19(2):132-143.

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