In order to accurately and definitively diagnose primary lung cancer in your dog, your vet will need to perform a physical exam as well as order several tests. A complete medical history and physical exam are important because they will establish a list of possible diagnoses. A physical exam may reveal abnormal or muffled lung sounds in your dog which may indicate dyspnea (difficult or labored breathing or shortness of breath). A vet will also listen to the heart to rule in or rule out heart disease as a likely cause of the symptoms. Many animals with fungal infections will also have enlarged lymph nodes or skin lesions.
After the physical exam, your vet may order any or all of the following tests and procedures to help determine the correct diagnosis.
Complete blood count – a CBC evaluates the red and white blood cells as well as the platelets. The results of this test are often normal in dogs with lung cancer, but it will help rule out infectious causes of the symptoms.
Biochemical profile – evaluates blood sugar, blood proteins, and electrolytes, as well as provides information about liver and kidney function. It is helpful for the vet to have an overall assessment of health, and may determine the need for further diagnostic testing.
Urinalysis – is part of a complete laboratory assessment and gives a better indication of kidney function than the biochemical profile alone.
Chest radiographs – X-rays of the chest are probably the single most important tool in making a preliminary diagnosis of lung cancer. X-rays will read looking for the presence of lung tumors, fluid in the chest cavity, the size of the heart and associated blood vessels, and an evaluation of the lung tissue. What is usually found on an x-ray depends upon the type of lung cancer? Primary lung cancer is frequently located in the caudal (towards the hind end of the pet) lung lobes, however can be located in any lung lobe and are usually a single mass in the lungs, unless the tumor has spread.
Metastatic lung tumors frequently are found in multiples and invade a variety of lung lobes. However, occasionally a metastatic tumor spread from elsewhere in the body may appear as a single mass in the lungs. If your dog has a fever and has been traveling to the southern United States, the masses in the lungs could be due to a fungal infection and can be treated with medication.
A CT scan may be ordered in lieu of or in addition to a standard x-ray. CT scans provide greater clarity and reveal more details than regular x-ray exams. It is one of the best and fastest tools for studying the chest because it provides detailed, cross-sectional views of all types of tissue. It is often the preferred method for diagnosing many different cancers, including lung since the image allows a physician to confirm the presence of a tumor and measure its size, precise location, and the extent of the tumor’s involvement with other nearby tissue.
Abdominal X-rays or abdominal ultrasound exam – Imaging studies of the abdomen may not be required in every case, but evaluation of other organs is a good screening test for evidence of metastasis of a primary lung tumor to other sites. Although many tumors spread from other sites to the lungs, primary lung tumors can spread throughout the lungs, as well as to other parts of the body.
Fine needle aspirate of the lung mass – If there is a mass that is big enough and close enough to the chest wall, an aspirate of the mass may be attempted with a hypodermic needle and syringe. This involves passing a needle through the chest wall and inserting it into the mass, then gently creating suction on the syringe to remove microscopic cells for evaluation. This is a fairly safe procedure but should be done using ultrasound guidance to determine the exact location of the mass. The dog may need to be sedated for this test.
If the dog has pleural effusion (abnormal accumulation of fluid) this can be safely and routinely removed from the chest without ultrasound guidance. Removal of fluid may help the dog breathe easier as well as provide fluid for analysis and possible diagnosis. These methods may allow the doctor to make a diagnosis without undertaking a more invasive procedure, but it should be noted that a sample from a fine needle aspirate is never as good as a piece of tissue for biopsy evaluation.
Trans-tracheal aspirate or bronchoscopy – A trans-tracheal aspirate is a procedure in which sterile fluid is introduced into the trachea and fluid and cells are suctioned out. This can sometimes be another method to obtain a diagnosis. However, this is often more useful if there is evidence of widespread lung disease rather than a single mass. This test can be performed under light sedation.
A bronchoscopy study involves placing a scope into the trachea and smaller airways. The interior of the airways can be examined by this method and samples can also be obtained for analysis. Single masses in the lung tissue cannot be seen via this method, but a mass associated with one of the airways may be sampled using this technique.
Biopsy of the lung mass – Tissue samples from a lung mass are often the only definitive way to make a diagnosis of lung cancer and help to specify which form of lung cancer it is. The most common procedure to obtain a sample of the mass is exploratory thoracotomy, which involves opening the chest cavity surgically. Often the mass can be completely removed while performing this procedure. Therefore, surgery can play both an important diagnostic as well as a therapeutic role in the management of the disease.
A second potential way to obtain a lung mass biopsy is by thoracoscopy. This procedure is performed using a scope, which is placed into the chest through a smaller incision than what would be used for surgery. The scope is a long tube with an attached camera, which allows visualization within the chest cavity. Depending on mass location, a biopsy may be taken using this method. However, it is unlikely that the mass could be removed using the scope. Finally, in certain cases, ultrasound-guided biopsies may be performed. This is the least invasive way to obtain a biopsy but is not always the best way to diagnose lung cancer as the sample size will be smaller than with thoracoscopy and may be a riskier procedure for some dogs.
The diagnosis of metastatic lung cancer can be done with any of the above methods. However, it is generally accepted that if there is a known tumor somewhere in the body and masses are found in the lungs, it is presumed that these are metastatic tumors and many of the invasive procedures to diagnose the disease are not necessary. Surgical excision of the tumor is often the first step used to treat canine lung cancer if the dog is otherwise in good health. It is the treatment of choice for dogs with primary lung tumors. However, depending on the size and location of the mass, complete or even partial removal may not be possible. If there is evidence of widespread involvement, surgical removal is generally not an option.
In the majority of primary single lung tumors, the lung lobe that is involved is totally removed with the mass. This is called a thoracotomy and lung tumor removal. Usually, the tumor is removed through the side of the chest cavity (lateral thoracotomy). In some cases, the breast bone must be divided (median sternotomy) so that both left and right lungs can be accessed. If needed, the entire left lung can be removed at one time, as the right lung will take over for the left. Your dog may not do as well if the entire right lung (all lobes) needs to be removed.
Please be aware that this is major surgery and will require time and dedicated home care for your dog to recover fully. Post-surgical responsibilities will include:
Limit exercise to short leash walks for 3 weeks if a lateral thoracotomy was performed; limit exercise for 6 weeks if a median sternotomy was performed
- Administer oral pain medications as needed
- Monitor respirations to make sure that these are not labored
- Monitor gums and tongue to make sure that these are pink
- Encourage eating
- Monitor the incision for signs of infection
- Do not allow licking or scratching of the incision
Depending on the type of tumor, chemotherapy or radiation therapy may be recommended in addition to surgery to prevent the spread or resurgence of malignant tissue.
If surgery is not an option, chemotherapy may be used to slow the progression of the disease. Although there is little evidence to show that chemotherapy is very effective in most primary lung cancers, there are reports of some dogs doing well (see Snuggy’s story). Both vinblastine and/or carboplatin are generally used as chemotherapy drugs. Radiation therapy is sometimes used for the treatment of lung cancer in dogs depending upon the proximity of the lung tumor to the heart.
Metastatic lung cancer can be treated with radiation or chemotherapy. Surgical intervention is not usually recommended but may be possible depending on certain clinical criteria. If there are three or fewer lung nodules affected, surgery can be done to remove these in order to increase the lifespan of your dog. This is most commonly done with osteosarcoma metastatic disease
Survival times following conventional standard treatments range from two months to two years, depending primarily on whether cancer has spread to lymph nodes or elsewhere in the body before surgery.
Because lung cancers are highly dependent upon angiogenesis for their growth and spread, antiangiogenic therapy may be useful for this condition. Studies of lung cancer in animals have clearly shown that the greater the number of microvessels within the lung cancer, the worse the prognosis. Angiogenesis inhibition has slowed lung cancer growth significantly in animals. Researchers have shown that a drug mimicking the natural angiogenesis inhibitor thrombospondin-1 can inhibit lung cancer in animals. A similar drug, called ABT-510, is now in veterinary trials for canine cancer. In human patients, other antiangiogenic drugs have been used to treat lung cancer, including Avastin, Neovastat, TNP-470, squalamine, and endostatin.
Because Avastin is not available for use in dogs at this time (in humans the cost can run up to $100,000 per year), some vets are prescribing metronomic or low dose chemotherapy with Deramaxx (a non-steroidal anti-inflammatory drug (NSAID) and an oral chemotherapy drug, cyclophosphamide (Cytoxan). They believe this type of chemotherapy protocol works by inhibiting new blood vessel formation which is required for new tumor growth, similar to antiangiogenic therapy. This type of chemotherapy has not been specifically investigated for lung cancer in dogs. It has shown some benefit in delaying the recurrence of hemangiosarcoma and soft tissue sarcomas in dogs. This protocol may be worth trying if other chemotherapy agents do not prove useful in fighting this form of cancer.
The prognosis is generally good for dogs with primary lung cancer presenting with a single, small mass in their lungs that has not spread to the lymph nodes or other tissue. In this group, more than 50% are expected to live 1 year after the surgical removal of the mass. A recent study of 67 dogs diagnosed with primary lung cancer showed that the prognosis depends on several factors such as the cancer histological type, grade, how advanced the cancer is, and whether the pets had symptoms at the time of diagnosis The overall median survival of these dogs was 1 year. Dogs with lower-grade tumors had a median survival of 22 months whereas dogs with higher-grade tumors had a median survival of 6 months. Dogs who showed symptoms had a median survival of 8 months compared to 18 months in those without symptoms.
Following wide surgical resection of the pulmonary mass, dogs with pulmonary adenocarcinomas are reported to have a longer mean survival time than animals with other types of primary lung carcinomas.