Mesothelioma in Dogs

Canine mesothelioma represents a rare variety of cancer that affects the mesothelium, a lining that protects the pericardial, peritoneal and pleural cavities. This lining consists of a single flattened layer of ectodermal cells that line the aforementioned body cavities as well as the tunica albuginea of the testes.  

Occurrence of Mesothelioma in Dogs

Dogs aged 8 years or more are more predisposed to this health condition. However, cases of dogs aged between 7 weeks and 15 years suffering from mesothelioma have been reported. Mesothelioma discovered in 7 weeks old puppies is believed to have a congenital nature. Some of the breeds that are at a greater risk of developing such a tumor include:

  • Bouvier des Flandres
  • German shepherd dogs
  • Irish Setters

Also, the gender seems to affect the occurrence of this disease, as it seems to be more common in males than in females.

Causes of Mesothelioma

As in the case of humans, the main cause of this disease is represented by exposure to asbestos. One of the two types of asbestos fibers, amphibole asbestos, is associated with a greater risk of tumor development. Ferruginous bodies abnormal both in type and numbers have been discovered in dogs suffering from mesothelioma. Another possible cause is exposure to certain chemicals such as pentachlorophenol.

Signs and Symptoms

In the order of incidence, mesothelioma affects most frequently:

  • Pleural cavity
  • Peritoneal cavity
  • Pericardial cavity

Keep in mind that the tumor may affect more than one body cavity at a time. As the cancerous mass occupies a lot of space, one of the main symptoms of mesothelioma is dyspnea. This symptom may also be caused by body cavity effusions, which are accompanied by such signs as:

  • Abdominal discomfort
  • Cough
  • Exercise intolerance
  • Lethargy
  • Respiratory distress
  • Tachypnea

In case your dog exhibits any of these symptoms you need to take him to a veterinarian in order to have the problem diagnosed.

Diagnosis of Malignant Mesothelioma

Mesothelioma is particularly difficult to diagnose in the early stages. A physical examination is necessary for detecting the effusions, and additional tests such as the following may be required for determining the cause of the effusion:

  • Biochemical profile
  • Complete blood cell count
  • Radiographs
  • Ultrasound
  • Urinalysis

The ultrasound test is typically used for determining whether the cancerous mass affected the surrounding organs. In some cases, however, mesothelioma cannot be detected with ultrasounds or CT (computed tomography) as the surface of the viscera does not get penetrated. In case the tests do not provide conclusive results, the veterinarian may decide to make a biopsy. If the diagnosis is confirmed, a treatment needs to be started immediately.

Treatment Options for Canine Mesothelioma

Basically, there are two ways of treating mesothelioma: medication or through a surgical procedure. The latter does not always represent a viable option, as neoplasms may metastasize, affecting the surrounding organs. Unless mesothelioma is diagnosed when in the early stages, metastasis takes places and surgery is no longer taken into consideration.

Prior to starting chemotherapy, a veterinary oncologist needs to be consulted. While chemotherapy with prednisone, cyclophosphamide and vincristine does not lead to remission, mitoxantrone and doxorubicin caused a complete remission of mesothelioma in some cases. However, the best results are currently obtained with a treatment called intracavitary cisplatin.