Lung tumours in dogs: symptoms, tests and treatment

Overview

A primary tumour, which starts in the lungs, is rare in dogs. Primary lung tumours account for around 1% of all canine tumours. Tumours that have spread to the lungs from elsewhere are more common in pets than primary lung tumours. Most primary lung tumours are malignant.

Common types include adenocarcinomas, which arise from glandular cells. Benign adenomas also occur, but are rare. Around 25% of dogs show no symptoms associated with a primary lung tumour. An asymptomatic tumour may be found on a chest X-ray taken for another reason.

Around 85% of malignant primary lung tumours in dogs arise from epithelial cells, which line surfaces. Pulmonary histiocytic sarcoma is another possible malignant tumour type.

Causes

A primary lung tumour usually starts in the small airways or air sacs. Besides glandular tissue, tumours can arise from the lungs' supporting tissues. Fibrosarcoma, for example, arises from connective tissue. Haemangiosarcoma arises from blood vessels.

Cancer cells can travel to the lungs through the bloodstream and form secondary tumours. Cancer can also spread to the lungs through the lymphatic system or directly from neighbouring tissues. Mammary cancer, bone cancer and oral melanoma are examples of cancers that readily spread to the lungs. A primary lung tumour can also spread to other parts of the lungs.

Spread along the airways has been described in around 50% of dogs with pulmonary adenocarcinoma. Genetic changes affecting the regulation of cell growth may drive tumour growth.

A tumour arising from cartilage is called chondrosarcoma. The lungs may be the only site of secondary tumours from a cancer elsewhere. Sometimes a lung tumour develops as a separate primary tumour alongside another tumour.

Risk factors

Primary lung tumours are diagnosed at an average age of 10–12 years in dogs. No consistent sex predisposition has been established. Evidence of a breed effect is also inconsistent. Boxers and Bernese Mountain Dogs are among the breeds that may be more susceptible.

Tobacco smoke and some air pollutants are considered possible risk factors for lung tumours. However, a causal link between passive smoking and canine lung cancer is uncertain. A questionnaire-based comparison including 135 dogs with lung tumours found no association with passive smoking.

Dogs with anaplastic, or poorly differentiated, carcinoma are often younger than usual, averaging 7.5 years old. Carbon dust accumulation in the lungs, called anthracosis, has been associated with an increased risk of lung cancer.

Typical symptoms

Possible symptoms include:

• A persistent dry cough without bringing up mucus.

• Faster breathing than usual at rest.

• Breathlessness or visibly laboured breathing.

• Tiring on walks and reduced exercise tolerance.

• Reduced appetite.

• Unintentional weight loss.

• Reduced energy.

• Lameness without an obvious limb injury.

Coughing up blood has been described in 3–9% of dogs with lung carcinoma. Coughing has been reported in 52–93% of symptomatic dogs with lung carcinoma. Some dogs lose weight despite maintaining a good appetite.

A tumour can cause regurgitation by pressing on important structures in the chest. An absence of respiratory symptoms does not rule out a tumour. In a series of 61 dogs undergoing surgery, ten, or 16%, showed only non-respiratory signs.

Breathlessness has been described in 6–24% of dogs with lung carcinoma. Reduced energy has been reported in 12–18% of patients. Lameness has been reported in around 4%.

Complications and consequences

A large tumour mass, secondary tumours or fluid accumulating in the chest cavity can cause sudden difficulty breathing. A primary lung tumour can spread to the bronchial lymph nodes. Secondary tumours can also develop in the bones and brain. Lameness may result from new bone formation beneath the periosteum of the limbs, called hypertrophic osteopathy.

The extent of spread affects the outlook after surgery

In follow-up of 61 dogs operated on between 2007 and 2017, the outlook depended particularly on tumour size and spread. Median survival after surgery for a tumour that had spread to lymph nodes was 41 days. Without detected lymph node spread, the corresponding median was 570 days.

For tumours smaller than 3 centimetres, median survival was 1,155 days. For tumours measuring at least 3 centimetres, it was 330 days. Dogs with other tumour deposits in the lungs had a median survival of 125 days. Without pulmonary metastases, the corresponding median was 630 days.

Tumour recurrence or spread is a common tumour-related cause of death. The outlook for cancer that has spread to the lungs from elsewhere is generally poor.

In the same surgical follow-up, median survival was 330 days for tumours near the base of a lung lobe. For tumours at the edge of a lung lobe, it was 650 days. Long-term follow-up information was available for 50 dogs.

Diagnosis at the vet

Imaging and checking for spread

Investigations usually start with chest X-rays. A lung tumour may appear as one or several defined masses. Sometimes the abnormality resembles a more extensive area of dense lung tissue. Listening to the lungs may reveal no abnormalities despite a tumour being present.

Computed tomography, or CT, also reveals changes that cannot be seen on X-rays. As well as lung abnormalities, CT assesses regional lymph nodes. Abdominal ultrasound can help find the original tumour when cancer has spread to the lungs. Blood and urine tests check for other diseases before treatment.

Records of previously removed tumours help investigate the origin of secondary tumours. The extent of spread is assessed before surgery. Staging considers the tumour itself, lymph nodes and distant metastases.

Whether small tumour deposits are visible depends on the imaging method. In a comparison involving 18 dogs, X-rays showed only 9% of the lung nodules detected by CT. The smallest nodules visible on CT measured 1 millimetre. In the same comparison, nodules smaller than 7–9 millimetres were not visible on X-rays.

Cell and tissue samples identify the tumour type

A fine-needle sample can be taken from a mass near the chest wall. Sampling can be guided by ultrasound or CT. The cells are examined under a microscope to identify the tumour type. A tissue sample can confirm the definitive diagnosis.

Histological examination of the removed lung lobe identifies the tumour type. Sampling the bronchial lymph nodes during surgery is also important. A small needle biopsy is not always enough to assess how differentiated a tumour is. Sampling through the chest wall carries a risk of pneumothorax or bleeding into the lung.

Treatment

Surgery is particularly suitable for a localised tumour

Surgery is usually the first-choice treatment for a solitary primary lung tumour. The entire affected lung lobe is usually removed. A small tumour at the edge of a lobe can sometimes be removed by partial lobectomy. The right and left lungs comprise several lobes that can be removed individually.

Surgery may involve opening the chest or, in suitable cases, a thoracoscopic approach. Thoracoscopy is particularly suitable for selected tumours at the edge of a lung lobe. Regional lymph nodes are also assessed during surgery. When there are multiple secondary tumours, medical treatment may be considered instead of surgery.

After surgery, a chest drain removes air and fluid accumulating in the chest cavity. The drain usually stays in place for 12–24 hours. Possible surgical complications include bleeding and air leaking from the closed bronchial stump. Adequate pain relief helps the dog breathe deeply after surgery.

The dog can go home once the drain has been removed, breathing is satisfactory and pain is controlled with oral medicines. Exercise is usually restricted for 10–14 days to allow the wound to heal. Stairs may be difficult for up to two weeks. A protective collar can prevent wound licking.

Other cancer treatments and symptom relief

Chemotherapy may be considered for a tumour that has spread or is unsuitable for surgery. However, reliable evidence of its effectiveness against canine lung carcinoma is limited. Medical treatment may aim to slow disease progression and maintain a good quality of life. Other diseases are also considered when choosing treatment.

Precisely targeted stereotactic radiotherapy may offer an alternative to surgery for selected patients. Suitability is usually assessed with CT. Radiotherapy is given under anaesthesia to prevent movement. It can cause scarring of the lung tissue around the tumour.

Symptomatic care aims to reduce pain and other discomfort. Nausea, vomiting and loss of appetite can be managed with supportive medicines chosen by the vet. Nutritional status is assessed at diagnosis and during treatment. The dietary goal is palatable, nutritionally complete food that the dog eats in sufficient amounts.

Median survival in 19 dogs treated with stereotactic radiotherapy was 343 days. Of these dogs, 38% were alive after one year. In the same follow-up, median progression-free time was 238 days. Treatment targeted 21 primary lung carcinomas in total.

Pain management combines treatments that work in different ways when needed. Other diseases, such as pancreatitis or kidney disease, are also considered when choosing a diet. Persistent loss of appetite may require a feeding tube if medication is insufficient.

The vet plans medical treatment according to the confirmed tumour type and extent of spread.

Prevention

Stopping smoking is recommended to prevent the dog's exposure to tobacco smoke at home. Smoke residues are carried indoors on hair and clothing even when smoking takes place outside. Asbestos is another potentially harmful environmental exposure. Avoiding smoke is a precaution: a causal link between passive smoking and primary lung cancer in dogs has not been confirmed. When cancer has already been diagnosed elsewhere in the body, a key treatment goal is to prevent cells spreading from the original tumour and forming new secondary tumours in the lungs.

Important for dog owners

If your dog has difficulty breathing, take them to an emergency vet quickly and calmly. Keep the car cool during transport. Heat can increase panting and worsen breathing.

Record when coughing began, changes in exercise tolerance, appetite and weight. Bring results relating to previous tumours and details of current medicines to the consultation.

Follow-up imaging can check for tumour recurrence or spread after surgery. Chemotherapy can cause vomiting, nausea, diarrhoea and bone marrow suppression. Raw feeding is not recommended for dogs with cancer because of the increased risk of bacterial infection.

Agree with the treating vet whom to contact if new symptoms or treatment side effects develop. At home, also assess your dog's sleep, mobility and interest in familiar activities.

Frequently asked questions

Can a dog have a lung tumour without coughing?

Yes: around 25% of dogs with a primary lung tumour have no symptoms. The abnormality may be found incidentally on an X-ray taken during another investigation. Some dogs mainly show weight loss or reduced energy. Listening to the lungs may also reveal no abnormalities at all.

Are lung metastases the same as primary lung cancer?

Metastases are cancer that has spread to the lungs from elsewhere in the body. A primary tumour starts in the lung tissue itself. There are usually fewer treatment options for metastases than for localised cancer arising in the lungs. Abdominal ultrasound is one way to look for the source of metastases.

Can a dog's lung tumour be removed surgically?

A solitary, localised primary tumour can often be removed surgically. The entire affected lung lobe is usually removed. The extent of spread is assessed before the procedure. Lymph node status has a major influence on the outlook after surgery. Other diseases also affect treatment planning.

Why does the vet recommend a CT scan?

CT helps find small lung abnormalities that are not visible on ordinary X-rays. It also assesses regional lymph nodes. Information about spread helps guide treatment and assess the outlook. Cell or tissue samples are also used to identify the exact tumour type.

How long can a dog live with a lung tumour?

Survival depends on factors including tumour size, type and spread. In follow-up of dogs undergoing surgery, median survival without lymph node spread was 570 days. With lymph node spread, the corresponding median was 41 days. Tumour recurrence is a common tumour-related cause of death.