Lung cancer is sadly common in humans, especially when linked to factors like active and passive smoking, air pollution, and asbestos exposure. While cats don’t tend to smoke, do they still get lung cancer? What are the symptoms of lung cancer in cats? What do vets do if your cat gets lung cancer?
Role of lungs
Let us first outline the role of the lungs, so you can better understand how cancer affects them, and why certain symptoms occur. The primary role of the lungs is as part of the respiratory system – air enters the lungs saturated with oxygen. In tiny air sacs, called alveoli, oxygen is exchanged into the bloodstream in return for waste carbon dioxide. This CO2 is removed from the body in exhaled air. Each lung contains millions of alveoli, which increases the surface area available to exchange gases, making the lungs very efficient.
As well as respiration, the lungs are responsible for balancing acidity and alkalinity (pH) in the body. The body requires a certain pH range for bodily processes to take place effectively. Should this balance be upset, disease can occur. One of the ways the body maintains this homeostasis is by controlling the breathing rate – if the body detects the pH is getting too low (too acidic) the respiration rate increases, removing more CO2 from the body. CO2 is a component of carbonic acid. Less CO2 means less carbonic acid, meaning acidity drops and pH rises. Conversely, if the body is too alkaline (high pH), the respiration rate will slow to conserve CO2 and increase acidity.
The lungs also help protect the body from infection by creating and removing mucus that traps debris, bacteria and viruses (this is why we have mucousy coughs when we are ill). Parts of the lung are also rich in white blood cells to fight pathogens that escape the mucous. The lungs also play a role in vocalisation (and speech), and can absorb or excrete certain chemicals such as inhaled drugs or hormones.
Feline Lung Cancers
Cancer Overview
Cancer is the uncontrolled growth of cells in the body. Most body cells divide regularly, and with every division there is a small chance the cells can mutate to form cancer cells. The majority of these are quickly identified and destroyed by the body, but a few can escape notice and replicate further. This group of cells can grow to form masses called tumours (though not all cancer forms tumours). External factors, like chemicals, radiation and infections can increase the chance an animal will get cancer. Most cancers, though there are a few exceptions, cannot be spread to another animal.
Less destructive cancers are benign, while more aggressive, invasive and destructive cancers that cause more serious disease are considered malignant. Cancer can remain local, or spread via growth, the bloodstream, lymphatic system or nerves – these secondary cancers are known as metastases. Common sites for cancers to metastasise to are local lymph nodes, liver, spleen and lungs. The original tumour is called the primary cancer, while any spread from it is secondary.
Primary Lung Cancers in Cats
Primary lung cancer (cancer that first developed in the lungs) is comparatively rare in cats, though the numbers do seem to be increasing (perhaps because we are better at diagnosing them, or because cats are more exposed to pollution, or simply because cats are living longer). Most of these are diagnosed in cats aged 12 years, and male and female cats are equally predisposed. Persian cats may be slightly more prone to lung cancer than other cats. Sadly, approximately 80% are malignant.
The three main primary lung cancers in cats are:
- Pulmonary adenocarcinoma – cancer of the glands of the airways. Around 80% of primary lung cancers in cats are these.
- Bronchogenic carcinomas – cancer of the airways themselves. Only 11% of primary cancers.
- Squamous cell carcinoma – cancer of the tissue lining the airway. 7% of primary cancers.
Other cancers include histiocytic sarcoma (cancer of the immune cells) and granulomas (benign accumulation of cells).
Primary lung cancer in cats can spread to the skin, eyes, muscle, bone and organs, and notably the toes (more on this later).
Secondary Cancers
Secondary cancers, those that have spread from a primary cancer elsewhere in the body, are much more common in cats. Almost any cancer can spread to the lungs, but in cats the most common include lymphoma, squamous cell carcinomas (skin cancer), mammary gland adenocarcinomas (breast cancer) and hemangiosarcomas (cancer of the spleen and blood vessels). Most secondary lung cancers are malignant, due to the metastatic spread, and often by the time they are identified the primary cancer is quite advanced.
Symptoms of Feline Lung Cancer
The symptoms of feline lung cancer are varied and will depend on the size of the tumour, the location within the lungs, how quickly the tumour is growing and if there is already underlying disease such as feline asthma.
By far the most common presentation of a cat with lung cancer is having no symptoms
Many cats will develop tumours in the lungs with no obvious change in the early stages. This unfortunately means many lung cancers are only identified in the end-stages of the disease. Routine health checks, blood work and even radiography can help identify cancer earlier.
Many of the other more common symptoms in cats are quite vague
Again, this makes diagnosing lung cancer difficult. These include lack of energy and lethargy, weight loss, anorexia and general dullness. Symptoms related to the lungs include loud or laboured breathing, rapid breathing (anything above 30 per minute should be noted, and above 40 is a concern), and wheezing. These symptoms are related to the lungs being damaged and thus less efficient. Coughing can occur but is rarer in cats than dogs. Pressure due to fluid building up around the lungs can lead to swelling of the head, neck and abdomen, and vomiting and diarrhoea. Some cats may have a fever as well.
Cats can also get a strange condition called lung-digit syndrome
This is where a cat will unexpectedly become lame due to the spread of a primary lung cancer (often adenocarcinoma) to the toes. In many cases a primary cancer is only identified after the unexplained lameness has been investigated. Common symptoms include pain in the toes, swollen digits, discharge from the nail and loss of the nail. Though damage and infections in the nail are common in older cats that use their claws less frequently, studies have found as many as 1 in 8 of these cases are associated with primary lung cancer.
Diagnosing Feline Lung Cancer
There are a number of steps a vet may take to identify lung cancer in cats. To start with, a vet will take a thorough history, asking what symptoms there are, how long the symptoms have been going on for, are they worsening, and so on. As we explained above, many of the symptoms of lung cancer in cats are quite vague, but they may indicate to the vet there is a problem that needs investigating.
Your vet will then perform a clinical exam, checking your cat from nose to tail for any other symptoms. Should lung cancer be suspected, they will want to auscultate your cat’s heart and lungs, check their respiratory rate and listen for any abnormal sounds within the lungs. They might also find associated symptoms like muscle loss, a temperature or pain in the feet.
From here, a vet may recommend various steps
Routine bloodwork is always a good starting point – some cancers will result in changes in the blood parameters, such as an increased calcium level, high or low white blood cell count or anaemia. This will also help rule out other common causes of illness in older cats, such as chronic kidney disease, liver disease and hyperthyroidism. Urinalysis may be recommended for similar purposes.
Imaging is the best way to identify the presence of cancer, and an x-ray of the chest is a good starting point. Large primary tumours as well as smaller metastases can be identified on an x-ray. Associated changes such as secondary pleural effusion or heart disease may be seen as well. Unfortunately, x-rays are not completely sensitive, meaning small tumours under a few millimetres in size may not show up. In these cases, or where more information is needed, a CT scan (a three-dimensional x-ray) is much more sensitive. Other imaging modalities, such as ultrasonography or MRI may be useful to find tumours elsewhere in the body, such as within the abdomen.
The only way to definitively diagnose the type of cancer, and thus the overall prognosis, is with a biopsy. This means taking a piece of the tumour to be tested by a laboratory. This can be done surgically or via large biopsy needles – most of the time this requires a full general anaesthetic, which can be risky in unwell elderly cats.
Treatment of Lung Cancer in Cats
Treating feline lung cancer is dependent on the type of cancer – this is why in an ideal situation a cat with cancer would have the primary tumour biopsied. Unfortunately, this may not always be practical and a vet may have to treat the cancer presumptively or palliatively.
Primary lung cancers can sometimes be removed surgically
This involves a general anaesthetic and entry into the thoracic cavity, which are risky procedures for older cats. Most vets in first opinion practices will want to refer these cases to specialist surgeons. If the tumour is localised to one lung lobe only, this can give the cat a year or more before the cancer returns. Should a primary cancer have already spread, removal of the primary tumour is unlikely to increase the cat’s lifespan, and surgery most likely will not be recommended. Following surgery, some cats may be recommended chemotherapy or radiotherapy to kill any remaining cancer cells. These treatment options may increase the cat’s life expectancy or even completely cure the cancer in some cases.
Secondary lung cancers are much harder to treat
As we discussed above, by the time many are identified the primary cancer is already in advanced stages. There are generally no surgical options to remove secondary lung cancers, though surgery may be an option to remove the primary cancer elsewhere in the body. However, this is unlikely to change the life expectancy, so would only be recommended if the surgery would improve the cat’s quality of life. As with primary tumours, chemotherapy and radiotherapy may help treat the cancer in some cases.
Many cats with lung cancer will also receive adjunctive treatment to help improve their quality of life
These include anti-inflammatory drugs to reduce pain and swelling, appetite stimulants, pain killers, antibiotics to fight secondary infections, cough suppressants, anti-emetics for nausea and more. Should the cancer be unable to be cured, most vets would consider this palliative care.
In many cases where the cancer is identified too late or cannot be treated effectively, having the animal euthanised is recommended to prevent any suffering.
Prognosis and Prevention of Cats with Lung Cancer
Unfortunately, the prognosis for most lung cancers in cats is quite poor. Primary lung cancer, if identified before it has spread to other parts of the body and can be removed via surgery, chemotherapy and radiotherapy, has a higher prognosis. The mean survival time (MST, the time that half of patients will still be alive) for a cat with a well-differentiated carcinoma of the lung is 23 months. However, this can be as little as 2.5 months for poorly differentiated carcinomas, 67 days for those with feline lung-digit syndrome, and 73 days for those with spread to lymph nodes. Secondary metastatic lung cancer also has a poor prognosis, ranging from days to months by the time it is identified. Most of these cats will require euthanasia not long after diagnosis.
While an owner cannot completely prevent a cat from getting lung cancer, as many factors are either genetic or uncontrollable, there are things owners can do to reduce the risk. To start, ensuring your cat is generally healthy, up to date with their annual vaccinations, free of other diseases including obesity, and has a high-quality diet will go a long way to improving their quality of life should they get cancer, and may even reduce the risk in some cases. There is a proven link between cigarette smoke and cancer in cats, so avoiding smoking around your cat is important. Similarly, minimising their exposure to smog, asbestos, and other aerosol pollution is sensible too.
Further Reading:
Lung function: What do they do, and how to test their function
Lung Cancer In Cats | PetCure Oncology
Cancers and Tumors of the Lung and Airway in Cats – Cat Owners – MSD Veterinary Manual
Lung Cancer in Dogs and Cats – Veterinary Partner
Feline lung–digit syndrome: Unusual metastatic patterns of primary lung tumours in cats – ISFM
Environmental Causes of Cancer in Pets – WSAVA2007 – VIN
Unusual metastatic patterns of primary lung tumours in cats – JFMS Do dogs get lung cancer? – Vet Help Direct
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