Cancer occurs when abnormal cells grow in an uncontrolled way. These abnormal cells can damage or invade the surrounding tissues, or spread to other parts of the body, causing further damage. Most cancers start in a particular organ.
Lung cancer (pulmonary neoplasia) is a malignant tumour of the lungs which can be primary (originating in the lungs), or secondary (having originated elsewhere and spread to the lungs).
Primary lung cancer: This type of cancer is rare in cats, and accounts for less than 1% of all tumours. Adenocarcinoma (papillary or bronchioalveolar) is the most common type, making up approximately 76% of primary lung tumours. These tumours develop in the lining or inner surface of an organ and usually has glandular properties. Unfortunately, adenocarcinomas have a high rate of metastasis (spread to other parts of the body). Other types of primary lung cancer include anaplastic carcinoma and squamous cell carcinoma. The caudal lobe is the most common location of primary tumours in cats.
There has been an increase in primary lung cancer diagnosis, which may be due to advanced imaging techniques and/or the increase in the lifespan of domestic cats or an increase in the number of necropsies performed.
Primary lung cancers have a high rate of metastasis, between 76-80%, which can spread to regional lymph nodes or distant sites such as the bones, skin, brain, kidneys, spleen, liver and intestine.
The mean age is 12 years; there is no breed predilection; however, there is a higher incidence in female cats.
Secondary (metastatic) lung cancer is the most common type of cancer to affect cats. Cancer develops elsewhere in the body and spreads to the lungs via the bloodstream. Common cancers with the potential to spread to the lungs include oral, mammary, liver and bone.
Causes of lung cancer
Some possible causes of lung cancer may include:
- Exposure to cigarette smoke
- Environmental carcinogens (cancer-producing chemicals)
However, for most cats with primary lung cancer, the cause can not be determined.
Symptoms of lung cancer are often vague and non-specific and in-fact many tumours may be diagnosed as an incidental finding during chest x-rays for other diagnostic purposes.
Common symptoms of lung cancer include:
- Dyspnea (difficulty breathing)
- Tachypnea (rapid breathing)
- Exercise intolerance
- Loss of appetite
- Weight loss
- Cats with primary lung cancer (particularly adenocarcinoma) can develop a condition known as a lung-digit syndrome where cancer spreads to the digits of the feet, which results in bone lysis (destruction). Cats present with lameness, swelling of the toes and pain
There may be additional symptoms associated with tumours which have originated elsewhere on the body. For example, lumps or ulceration of the mammary glands of cats with secondary tumours which have spread to the lungs from the mammary glands. Symptoms may include:
- Lumps and bumps
- Ulcers which do not heal
- Blood in the urine or feces
- Changes to litter box habits
- Difficulty eating
- Changes in behaviour
Your veterinarian will perform a complete physical examination of your cat and obtain a medical history from you, including onset and type of symptoms. It will be necessary to perform tests to determine if your cat has cancer, the type, and location. These can include:
Baseline tests: To evaluate the overall health of the cat.
Xray: Chest x-rays which will reveal solitary or multiple masses, and in some cats, pleural effusion an abnormal build-up of fluid up in the pleural cavity, the thin fluid-filled space that lies between the lungs and the chest wall. Tumours less than 5 mm may not show up on an x-ray.
Computed topography (CT) or magnetic resonance imaging (MRI): These advanced imaging techniques can provide your veterinarian with a more accurate picture and diagnose smaller tumours (as small as 1 mm) and stage the tumour (size, shape, and invasiveness) as well evaluate for local lymph node involvement and to enable the surgeon to come up with a tailored treatment plan.
Fine needle aspirate/cytology: Ultrasound is used as a guide to obtain a sample via fine needle, which will be sent to a pathologist for cytologic evaluation (microscopic examination of the cells).
Surgical biopsy/histopathology: While fine needle aspirate is non-invasive, it is not as accurate as histopathology (microscopic examination of biopsied tissue). Cons are that it is more invasive.
Treatment depends on the size and location of the tumour. In most cases, your veterinarian will refer the cat to a veterinary oncologist, who specialises in the treatment of cancer. The treatment of choice is surgery to remove the affected lung/or portion of the lung as well as affected lymph nodes.
Pneumectomy: Surgical removal of the entire lung (pneumectomy).
Partial or full lobectomy: The lungs are made up of distinct lobes, and surgery may include removal and resection of part of the lung lobe (partial lobectomy) or removal of the affected lung lobe (lobectomy).
Chemotherapy: The use of chemotherapy drugs when surgery is not possible, to slow down tumour growth or as a follow-up treatment after surgery.
Stereotactic radiation therapy (SRT/SRS): An evolving modality for the treatment of lung cancer in cats which uses an advanced form or radiation therapy to destroy the DNA within the tumour to prevent the cells dividing. Healthy tissue close to the tumour is spared. SRT may be carried out in one session, or several (called fractions).
Thoracentesis: For cats with pleural effusion. Thoracentesis to remove fluid from the pleural cavity which allows the lungs to expand. The surgeon inserts a needle or drainage through the skin and into the pleural cavity to remove the fluid. A chest drain may remain in place for several days to help drain away excess fluid.
Unfortunately, most often, treatment is palliative and not curative.
The cat will remain in the hospital for several days post-surgery to recover and will receive supportive care such as analgesics to relieve pain.
The veterinarian will discharge the cat with a discharge sheet, on what to expect during recovery and how to care for your cat. Follow as directed and if you have any questions, contact your veterinarian.
Keep the cat indoors during recovery and avoid exercise.
Provide a quiet, clean, warm and comfortable place for your cat to sleep during recovery. Keep the cat’s litter tray and food bowls within easy reach.
The prognosis for cats with lung cancer is usually poor. Cats with a single tumour with no sign of lymph node involvement or metastasis have a more favourable prognosis.
Most cancers cannot be prevented, but there are some steps we can do to reduce the chances of the development of lung cancer in cats.
- Don’t smoke inside or around cats.
- Reduce the number of chemicals used in and outside the home. Switch to natural products where practical.
- Switch to dust-free cat litter.
- Schedule annual veterinary visits, while this can’t prevent cancer, early diagnosis can make treatment easier and hopefully avoid the spread from a primary location to the lungs.
- Keep your cat at a healthy weight.
- Desex (spay/neuter) your cat.