Cells in the lungs can degenerate and form a tumour. Lung tumours can spread through local ingrowth or through the bloodstream and / or lymph vessels and thus spread to other parts of the lungs, lymph nodes or spread even further.

Behaviour

Local spread was noted in 71% of malignant lung tumours, and metastases beyond the local lymph nodes were reported in 23% (for example, metastases to nervous tissue were reported). The risk of metastasis depends on the tumour type. For example, anaplastic carcinomas frequently spread (90%), followed by squamous cell carcinomas (50%), followed by adenocarcinomas and bronchoalveolar carcinomas.

Prevalence

These tumours are relatively rare in dogs (less than 1% at autopsy). The average age of diagnosis of lung cancer in dogs is 11 years, with the exception of a form known as anaplastic carcinoma, which occurs on average around 7.5 years of age.

Breed predisposition

Lung cancer may be more commonly found in the Boxer, Dobermann, Australian Shepherd, Irish Setter, and Bernese Mountain Dog vs other breeds.

Symptoms

Up to 30% of cases have no clinical symptoms at the time of diagnosis.

The most common clinical signs in dogs include: coughing (52-93%), followed by difficulty with breathing (6-24%), lethargy (12-18%), not wanting to eat or eating less (13%), weight loss (7-12%), coughing up blood (3-9%) and lameness due to a phenomenon known as hypertrophic osteopathy (4%). Symptoms generally only occur when the tumour size reaches at least 3 cm.

Physical examination

Aberrant neurological behaviour can occur as a result of metastases to nervous tissue.

Lameness may occur as a result of hypertrophic osteopathy in which new bone forms at a site remote from the primary tumour. The limping may improve after the lung tumour is removed.

Often a lung tumour does not cause abnormalities on auscultation (examination with the stethoscope) unless the process is extensive and / or because of fluid build-up in the lungs or the thoracic cavity.

Blood analysis

Often no abnormalities are found on blood tests.

Imaging

Radiography

The majority of lung tumours are diagnosed by chest radiographs. In a study involving more than 210 dogs with a primary lung tumour, more than half (53.8%) were found in a single lung lobe and 37.1% in multiple lobes.

The round white spots on the radiography indicate the presence of metastases

Ultrasound

Chest ultrasound can be used in some cases to assess a lung tumour or to obtain a tissue sample or aspirate.

CT-scan

A CT scan is recommended prior to surgery to be able to draw up a precise treatment plan. After all, CT scans can detect lumps in the lungs with dimensions of about 1 mm, while with radiographs this can only be done starting from 7-9 mm. Furthermore, CT scans of the chest are more accurate than chest radiographs in detecting metastases to nearby lymph nodes.

Sampling

If fluid accumulation in the lungs is present, a sample should be taken here.

Furthermore, broncho-alveolar lavages (the administration of fluid through a tube to the lungs, after which this fluid is withdrawn) could help to diagnose lung tumours. If a lung tumour is present, there is a good chance that the accumulated fluid contains cancer cells that can subsequently be recognized under a microscope. However, this approach is based on results obtained from a small group of dogs (14).

A fine needle aspirate of the lung mass provides a diagnosis in 38-90% of cases but is not possible in all cases due to the location of the presumed tumour.

A lung tissue sample prior to surgery can be done to find out if the nodule is a lung metastasis or a primary tumour. In the case of metastasis, surgery comprising of the removal of a part of the lungs is generally disregarded as an option.

The sampling itself can be done via a biopsy needle, an endoscope in the airways or an operation during which a part of the lung is removed. Tissue sampling of the lymph nodes at the branch between both lungs is recommended because spread to the lymph nodes significantly affects the prognosis and usually performed during surgery.

Histology

It is not easy to distinguish between a tumour that originates in the lungs (primary tumour) and a spread of another type of tumour, because a tissue sample is required for this. By means of a tissue staining, antibodies can be used that can distinguish between a primary lung tumour and a metastasis.

Surgery

Surgery is recommended for primary lung tumours that only affect a single lung lobe and have not yet metastasized. Based on the location of the tumour, part of or the entire lung lobe is removed. Depending on the required field of vision and location of the tumour, this procedure can be performed through an incision on the side of the chest, through the sternum or through an endoscope.

Chemotherapy

Little is known about how chemotherapy works for primary lung tumours. The clinical studies that have been carried out so far with different chemotherapy drugs have shown that varying, but often disappointing results have been achieved. Vinorelbine and cisplatin are used in humans and these chemotherapeutics are also expected to have the best effect in dogs. Research into the administration of an aerosol with chemotherapy drugs or cytokines (immune stimulating substances) led to good results against metastases in the lungs, less against primary tumours.

Little is currently known about the effects of treatment with tyrosine kinase inhibitors against lung cancer cells. Toceranib (TKI inhibitor) has been used successfully in some dogs, both in primary lung carcinomas and metastatic carcinomas, but more research is warranted to determine the clinical efficacy of TKIs in the management of dogs with primary lung tumours.

Immunotherapy

Little is currently known about the effects of treatment with monoclonal antibodies against lung cancer cells.

Radiotherapy

In humans, radiation is most often reserved for tumours considered non-removable. Because the region to irradiate isn’t immobile (breathing lungs), special techniques are used to provide a more precise delivery of radiation and spare unaffected tissues. Use of such treatment options remains to be investigated in dogs and cats with lung tumours.

Radio frequency ablation

Radio frequency ablation is a technique in which an electrode is inserted into a tumour, which is then heated. The cancer cells die as a result of this heat. This technique can be performed through the skin through CT guidance. This technique has already been experimentally tested on 5 dogs with good results but needs to be further explored.

The prognosis gets worse as

• the size of the tumour exceeds > 100 cubic cm (5.8 cm diameter)
• lymph nodes are affected. In a study after surgical removal of the primary lung tumour, dogs showed a median survival of 60 days when the lymph nodes were affected vs 285 days when they were not.
• there are metastases
• there are multiple tumours that grow into the surrounding tissues
• there are clinical signs at the time of diagnosis. Dogs without clinical signs showed a median survival of 545 days vs 240 days in dogs with clinical signs (based on one study).
• tumour tissue remains after surgery (median survival of 330 days (all removed) vs 28 days (when not all visible tumour tissue could be removed)
• the tumour type (longer survival in adenocarcinoma (19 months) vs squamous cell carcinoma (8 months))
• the entire lung lobe is involved
• the histologic grade is higher. A well-differentiated tumour (median survival of 790 days) has a better prognosis than a poorly-moderately differentiated one (median survival between 5-251 days)

The composition of the tumour tissue and the tumour size influence the prognosis. The higher the tumour grade and the larger the tumour, the worse the prognosis.