Unlike people where lung cancer is one of the top five cancers and the leading cause of cancer related deaths worldwide, primary lung cancer is very rare in dogs. Dogs are often diagnosed with lung cancer as in incidental finding during a routine geriatric screen.
Lung Cancer Symptoms in Dogs
Often dogs have NO clinical signs, but about half of dogs will have a non-productive (dry) cough that does not improve with antibiotics or cough suppressants. Other symptoms include difficulty breathing, increased breathing rate, cough with blood, and sometimes decreased appetite, lethargy, and weight loss. The changes in breathing can be due to what is called pleural fluid – fluid in the space around the lungs that makes is harder to breath.
Most often chest X-rays (three views) are done by the primary vet, and show a single, well-circumscribed lung mass. (Well-circumscribed means we can see the edges really well and it’s obviously not part of the structure of the lungs.)
Other recommended diagnostics may include blood work (CBC and chemistry panel) and urinalysis for general health screening.
Prior to surgery, I also want to make sure there aren’t other non-cancerous causes for the mass, like pneumonia, abscess, or a fungal granuloma, so I test to rule these out.
I also recommend abdominal ultrasound (to look for spread) and cytology of pleural fluid (in the chest around the lungs), if it is present.
I typically also recommend advanced imaging such as a CT, to detect metastasis to other lung lobes and evaluate the chest lymph nodes for spread. (CT is more accurate than X-Rays to evaluate the lymph nodes in the chest and additional masses in other lung lobes. CT can detect lung nodule as small as 1 mm but chest Xrays only detect nodules about 7-9 mm.)
Looking for spread is important, because in more than a third of cases multiple lobes are affected and this will change surgery options.
If the mass is up against the body wall, a transthoracic fine needle aspirates can be tried to make a diagnosis of cancer. You don’t want the need to pass through normal lung, possibly damaging the normal lung causing it to leak air into the chest acvity– so this is only an option if the mass is right next to the body wall. Usually fine needle aspiration is very safe, but in the case of lung masses, serious complications, while still rare, are important to note: air or bleeding into the thorax. The reason I suggest considering a fine needle aspirate if your dog’s mass is in this position is because the cytology (looking at the sample under a microscope) can confirm cancer, and eliminate another, benign cause.
However, in some cases we cannot make a preliminary diagnosis without surgery, and in many cases pre-surgery aspirate or biopsy is of questionable need.
Typically I recommend getting a biopsy first, and then planning a curative surgery from what we find out from the biopsy. In the case of lung cancer, though, surgery is trickier and involved than elsewhere in the body. Pre-treatment biopsy may not be necessary, considering the added costs and risks. Discuss the pros and cons with a surgeon or oncologist. You might find that doing a curative surgery without a biopsy first is the way you want to go.
Another option for those in areas with a qualified surgeon is thoracoscopy, which uses a fiber optic camera and small incisions in the chest to help distinguish cancer vs non-cancer. Thoracoscopy is less invasive, and in some cases it can also be used to remove an affected lung lobe.
Treatment and Prognosis:
Surgical resection is the best treatment option for primary lung cancer. This typically involves removing the affected lung lobe, also called a lobectomy or partial lobectomy. A lymph nodes biopsy should also be conducted. (Even lymph nodes that seem normal should be sampled since nodal spread is not always visible, and any lymph node spread has a negative effect on prognosis.)
In 50% of patients, the cancer is only in one lobe, and surgery is recommended as it offers the best chance for long term survival. Dogs that have a solitary (one) lesion, which is less than 5 cm in diameter, negative lymph nodes, no malignant pleural effusion, and well-differentiated adenocarcinomas have a better prognosis: a median survival time of one year.
In contrast, dogs that have lymph node metastasis have a median survival time of 1 to 4 months.
Survival times can be up to two years when other favorable factors are present. Favorable prognostics include no symptoms (like cough), normal regional lymph nodes on X-rays (or even better, on CT scan), no metastasis on lymph node biopsy, lower histologic grade, small tumors (<5 cm), no lung metastasis, a complete resection from surgery, and tumors that are on the outside edges of the lungs (called peripheral tumors), because these tumors are easier to remove completely.
(If your dog has some of these factors, but not others, unfortunately, there is no precise formula to predict how much extra time he may have — but your oncologist can help break it down as it relates to your dog’s specific case.)
Chemotherapy has shown to be of benefit in some cases after surgery, but not useful when used alone, without surgery to remove the primary tumor.
Carboplatin, cisplatin and vinorelbine appear to be most effective, but as is so often true with these uncommon tumors, we need more studies to know more about which protocols work best.
There has also been research into inhalational chemotherapy and cytokines. Intracavitary chemotherapy– injecting chemotherapy drugs directly into the abdominal cavity, rather than the bloodstream — has also been shown to have some success for dogs with pleural effusions. Most recently I treated a dog with mesothelioma with this technique of giving the chemo into the pleural space around the lungs (instead of into the veins).
NSAIDs may also be useful for their anti-angiogenic effect (they can target tumor blood vessels). Finally TKIs (tyrosine kinase inhibitors may also be useful, as TKIs can be beneficial in some subpopulations of people with non-small-cell lung cancer (NSCLC). Palladia and Kinavet are TKIs for dogs and it will be interesting to see if this can help dogs with primary lung cancer.
Live Longer, Live Well,
Sue Ettinger, DVM. Dip. ACVIM (Oncology). Dr. Sue is a boarded veterinary medical cancer specialist. As a Diplomate of the American College of Veterinary Internal Medicine (Oncology), she is one of approximately 400 board-certified veterinary specialists in medical oncology in North America. She is a book author, radio co-host, and an advocate of early cancer detection and raising cancer awareness. Along with Dr. Demian Dressler, Dr. Sue is the co-author of The Dog Cancer Survival Guide: Full Spectrum Treatments to Optimize Your Dog’s Life Quality and Longevity.