Mesothelioma is a rare cancer that affects the cell linings of the chest, abdomen and the membrane that surrounds the heart (the pericardium).
Rather than being a solid tumor, mesothelioma causes small nodules and thickening of the linings throughout the cavity it affects.
Mesothelioma is an exudative cancer, meaning it is very leaky and seeps fluid, which then collects in the chest, tummy or between the pericardium and the heart. Commonly, this fluid is bloody, but it can be a substance called chyle if cancer nodules block the lymph vessels that drain the region.
Symptoms of Mesothelioma in Dogs or Cats
In early stages, a cat or dog won’t show any signs other than being a little off-color.
Later, the symptoms that develop are due to the presence of fluid in the chest, belly or pericardial sac. This fluid puts pressure on the organs and causes symptoms such as breathlessness or a bloated tummy, depending on which cavity it invades.
In the chest, fluid causes the lungs to collapse — the animal takes rapid, shallow breaths through an open mouth. This is not normal for a cat at rest (some cats do get breathless and breathe through their mouths after energetic play) and should be mentioned to your vet.
Fluid in the belly causes it to swell and become distended. This squashes the stomach, and the pet may lose his appetite. As the swelling grows, the pressure compresses the diaphragm, which makes it difficult for the patient to breathe.
Fluid around the heart makes it difficult for the heart to fill with blood and be ready to pump it out around the body. This impairs blood circulation; the dog may faint or seem light-headed from time to time.
The most common fluid lost because of mesothelioma is blood, and so the patient becomes anemic. This shows itself as tiredness, getting wobbly with minimal exercise and heavy breathing at rest.
There is no specific test for mesothelioma, and screening bloods usually just presents anemia.
Further investigation involves chest X-rays and scanning the pet’s abdomen. If an area of thickening is identified on the scan, then an ultrasound-guided biopsy, or fine needle aspiration, is a great way to get a sample of cells to send to a histologist.
Analysis of fluid drawn from a cavity can also help. Although mesothelioma cells rarely exfoliate (they stay stuck to the chest wall), checking the fluid for cells associated with lymphoma, or other cancers, helps rule out other conditions.
Treatment of Mesothelioma in a Cat or Dog
Dogs can receive chemotherapy with a drug called cisplatin, although this drug is not safe to use for cats. Some animals are already very sick when the diagnosis is made, and the outlook for these patients is poor.
A measure of relief can be offered if fluid around the heart is causing the symptoms. A specialist surgeon can strip the pericardium away from the heart, and thus stop compression on this vital organ.
In humans, mesothelioma is associated with exposure to asbestos particles. Interestingly, tests on the lungs of dogs with mesothelioma of the chest cavity showed much higher concentrations of asbestos than in normal dogs. And even more intriguingly, most canine cases also have caretakers who have had contact with asbestos.
Given the suspicion that asbestos may be a trigger, and especially as it causes disease in humans, dog contact with asbestos should be rigorously avoided.
- Small Animal Oncology. Morris & Dobson. Publisher: Blackwell Science.
This pet health content was written by a veterinarian.